lecture #2 - university of michiganexphysio/mvs110lecture/readings/lec… · web viewin such...

Figure 4. Foundations of science: facts, laws and theories.

MVS 110 EXERCISE PHYSIOLOGY PAGE 1

READING #1INTRODUCTION TO SCIENCE

The Scientific Method and Exercise PhysiologyAs the academic discipline of exercise physiology emerged, so also developed research

strategies for objective measurement and problem solving, and the need to report discoveries of new knowledge. For the beginning exercise physiology student, familiarization with the methods of science helps to separate fact from “hype” - most often encountered in advertising about an endless variety of products sold in the health, fitness, and nutrition marketplace. How does one really know for sure whether a product really works as advertised? Does warming up really “warm” the muscles to prevent injury or enhance subsequent performance? Will breathing oxygen on the sidelines during a football game really help the athlete recover? Do vitamins “supercharge” energy metabolism during exercise? Will creatine, chromium, or vanadium supplements add muscle mass during resistance training? Understanding the role of science in problem solving can help to make informed decisions about these and many other questions. The following section examines the goals of science, including different aspects of the scientific method of problem solving.

General Goals of ScienceThe two distinct goals of science often seem at odds. One goal aims to serve mankind, to

provide solutions to important problems, and improve life’s overall quality. This view of science, most prevalent among nonscientists, maintains that all scientific endeavors should exhibit practicality and immediate application. The opposing view, predominant among scientists, maintains that science should describe and understand all occurrences without necessity for practical application - understanding phenomena becomes a worthy goal in itself. The desire for full knowledge implies being able to:

Account for (explain) behaviors or events Predict (and ultimately control) future occurrences and outcomes.

Regardless of one’s position concerning the goal of science, its ultimate aims include: Explanation Understanding Prediction Control

Hierarchy in ScienceFull appreciation of science requires

understanding its structure and three levels of conceptualization (see figure 1):

Finding facts Developing laws Establishing theories

Fact FindingThe most fundamental level of

scientific inquiry requires the systematic observation of measurable (empirical)


phenomena. Often referred to as fact-finding, this process requires standardized procedures and levels of agreement about what constitutes acceptable observation, measurement, and data recording procedures. In essence, fact-finding involves recording information (data) about the behavior of objects. While facts provide the “building blocks” of science, the uncovering of facts represents only the first level in the hierarchy of scientific inquiry.

Fact gathering occurs in many ways. We usually observe phenomena through visual, auditory, and tactile sensory input. Regardless of the observation method, to establish something as fact demands that different researchers reproduce observations under identical conditions on different occasions. For example, the healthy human heart’s four chambers and the average sea level barometric pressure of 760 mm Hg represent indisputable, easily verifiable “facts.” Facts usually take the form of objective statements about the observation such as: “Jesse’s body mass measured on a balance scale equals 70 kg (154 lb.), or “Jesse’s heart rate upon rising following eight hours of sleep averages 63 beats per minute.”

FOR YOUR INFORMATIONFACTS ARE FACTS…Facts exhibit no moral quality; once established, any question about facts arises only from interpretation. While some may disagree with the meaning and implications of an established fact (e.g., the average woman possesses 50% of absolute upper body strength of a male counterpart), no question exists about the “correctness” of the observation (that women have less upper body strength than males). In essence, a fact is a fact....

Interpreting FactsFact-finding evaluates the observed object, occurrence, or phenomenon along a continuum,

either imagined or real that represents its underlying measurable “dimension.” The term variable identifies this measurable characteristic. Frequently, quantification of the variable results from assigning numbers to objects or events to describe their properties. For example, consider the variable percent body fat with numerical values ranging from 3 to 60% of total body mass. Other examples include the weight of an object along a “heaviness” continuum, order of team finish in the NFL's American Conference, or heart rate from rest to maximal exercise.

Some variables like 50-m swim time or blood cholesterol level distribute in a continuous nature; they can take on any numerical value, depending on the precision of the measuring instrument. Continuous variables can further categorize into ordinal, interval, and ratio numerical data. Ordinal variables have rank-ordered values (e.g., small, medium, large bone frame size; first through tenth place finish in a race; standings in league competition) according to some property about each person, group, object, or event compared to others studied. In ordered ranking, no inference exists of equal differences between specific ranks (e.g., race time difference between first and second place finish equals difference between ninth and tenth place). Interval variables exhibit similar properties as ordinal variables, except the distance between successive values on an unbroken scale from low to high represents the same amount of change. For example, in marathon running, the temporal 20-minute difference between a finish time of 2 hr: 10 min and 2 hr: 30 min equals that of 3 hr: 50 min and 4 hr: 10 min. The ratio scale possesses properties of interval and ordinal scoring, but also contains an absolute zero point. Thus, a variable scored on a ratio basis with a value of 4 represents twice as much characteristic as a value of 2; this does not occur with interval-scored variables like temperature where 30°F is not twice as “hot” as 15°F.

In addition to continuous variables, some variables possess discrete properties. Scores for discrete variables fall only at certain points along a scale, like scores in most sporting events - “almost in” does not count in golf, soccer, basketball, or lacrosse. Discrete variables occur


when the score’s value simply reflects some characteristic of the object (e.g., male or female, hit or miss, win or lose, or true or false).

Casual and Causal RelationshipsA fundamental scientific process involves observing and objectively measuring the quantity

of a variable. However, it sometimes becomes more important to consider how data from one variable relate to data from another variable. Understanding how variables change in relation to each other represents a higher level of science than merely describing and quantifying diverse isolated variables. For example, quantifying the degree of association between maximal oxygen uptake capacity (abbreviated VO2max) and chronological age reflects a higher level of understanding than describing the “facts” concerning each variable separately.

An extreme example to illustrate that association between variables does not necessarily infer causality considers the strong direct association in western culture between the length of one’s trousers and stature (i.e., taller individuals wear longer-length pants than shorter counterparts). It seems highly unlikely that increasing trouser length would increase stature! In reality, this association is casual, not causal, being driven more by cultural mores that “require” trousers to descend to ankle level - and leg length relates closely with overall body stature.

The well established positive relationship between increasing age and increasing systolic blood pressure among adults does not necessarily mean that one should expect to inevitably become hypertensive with advancing years. Rather, the relationship exists between aging and blood pressure because other factors - sedentary lifestyle, obesity, arteriosclerosis, increased stress, and poor diet - often increase with age. Each of these variables independently can elevate blood pressure. From a scientific perspective, a change in one variable (X) does not necessarily cause changes in the other variable(Y), simply because X and Y relate in a manner that seems to “makes sense.”

FOR YOUR INFORMATIONCAUSALITY AND SCIENCETo infer causality, science requires that a change in the X-variable (independent manipulated variable) precedes a change in the Y-variable (dependent variable expected to change), with consideration, accounting for, or control of other variables that might actually cause the relationship. Understanding causal factors in relationships among variables enhances one’s understanding about observed facts.

INDEPENDENT AND DEPENDENT VARIABLES

Two categories of variables, independent and dependent, take on added importance when defining the nature of relationships among occurrences. This categorization relates to the manner of the variable’s use, not the nature of the variable itself. For causal relationships, manipulation of the value of the independent variable (X-variable) changes the value of the dependent variable (Y-variable). For example, increases in dietary intake of saturated fatty acids (independent X-variable) increase levels of serum cholesterol (dependent Y-variable), while decreases in saturated fatty acid intake reduce serum cholesterol levels. In other words, the value of the dependent variable literally “depends upon” the value of the independent variable.

For noncausal relationships, the distinction between dependent and independent variables becomes less clear. In such cases, the independent variable (e.g., the sum of five skinfolds or recovery heart rate on a step test) usually becomes the predictor variable, while the dependent variable (percent body fat or maximal oxygen uptake) represents the quality predicted. In some cases, an independent variable becomes the dependent variable, and vice versa. For example, body temperature represents the independent variable when used to predict change in regional blood flow or sweating response; body temperature assumes a dependent variable role when evaluating effectiveness of thermoregulation during heat stress.

Figure 2. Field study in exercise to estimate energy expenditure individuals pedaling a “surfbike”.


ESTABLISHING CAUSALITY BETWEEN VARIABLES

Scientists attempt to establish cause and effect relationships between independent and dependent variables by one of two methods:

Experimental studies Field studies

NATURE OF EXPERIMENTAL STUDIES

An experiment represents a set of operations to determine the underlying nature of the causal relationship between independent and dependent variables. Systematically changing the value of the independent variable and measuring the effect on the dependent variable characterizes experimentation. In some cases, the experiment evaluates the effect of combinations of independent variables (e.g., anabolic steroid administration plus resistance training; pre-exercise warm-up plus creatine supplementation) relative to one or more dependent variables. Regardless of the number of variables studied, an experiment’s ultimate goal attempts to systematically isolate the effect of at least one independent variable in relation to at least one dependent variable. Only when this occurs can one decide which variable(s) really explains the phenomenon. NATURE OF FIELD STUDIES

Field studies mostly investigate events as they occur in normal living. Under such “natural” conditions, it becomes impossible to experimentally vary the independent variable, or exert full control over potential interacting factors that might affect the relationships. In medical areas, field studies (termed epidemiological research) investigate the characteristics of a group as they relate to the risks, prevalence, and severity of specific diseases. To a large extent, “risk profiles” for coronary artery disease, various cancers, and AIDS have emerged from associations generated from field studies. In exercise physiology, a field study might involve collecting data during a “real world” test of a new piece of exercise equipment, as shown in Figure 2.

In this field experiment the subject wears a wristwatch that receives signals from a chest strap transmitter that sends the heart's electrical signals to the watch. The subject then pedals the “Surfbike” at different speeds to estimate heart rate during different exercise durations. Prior to the aquatic experiments, the subject’s heart rate and oxygen uptake were determined in the laboratory while pedaling a bicycle ergometer at different speeds. A linear relationship between laboratory determined heart rate and oxygen uptake allowed the researcher to “predict” the subject's oxygen uptake from heart rate measured during Surfbike exercise. An estimate of oxygen uptake permits calculation of caloric expenditure. In this particular experiment, Surfbike exercise at a heart rate of 178 beats per minute translated to 10.4 calories expended per minute.

While field studies provide objective insight about possible causes for observed phenomena, the lack of full control inherent in such research limits their ability to infer causality. Because neither active manipulation of the independent variable by the experimenter nor control over potential intervening factors occurs, no certainty exists that any observed variation in the dependent variable will result from variations in the independent variable.


Establishing LawsFact gathering generally does not generate much controversy; after all, facts are facts!

Interpretation of facts, however, raises science to a level rife for debate. Interpreting facts leads to the second level of the scientific process - creating statements that describe, integrate, or summarize facts and observations. Such statements are known as laws. More precisely, a law represents a statement describing the relationships among independent and dependent variables. Laws generate from inductive reasoning (moving from specific facts to general principles). Many examples of laws exist in physiology. For example, blood flows through the vascular circuit in general accord with the physical laws of hydrodynamics applied to rigid, cylindrical vessels. Although true only in a qualitative sense when applied to the body, one law of hydrodynamics, termed Poiseuille's law, describes the interacting relationships among a pressure gradient, vessel radius, vessel length, and fluid viscosity on the force impeding blood flow.

Laws are purposely not very specific; thus, they remain powerful because they generalize to many different situations. One variation of Hooke’s law of springs, made in 1678 by Robert Hooke (1635-1703), a contemporary of sir Issac Newton, states that elongation of a spring relates in direct proportion to the force needed to produce the elongation. Engineers apply this law to design springs for different kinds of instruments via simple calculations in accordance with Hooke’s law.

A good (useful) law accounts for all of the facts among variables. Many laws have limits because they apply to only certain situations. A limited law proves less useful in predicting new facts. A fundamental aspect of science tests predictions generated from a particular law. If the prediction holds up, the law expands to additional situations; if not, the law becomes restated in more restrictive terms. Developing new technologies often permits testing laws in situations heretofore thought impossible; this allows for development of a more comprehensive law.

Laws do not provide an explanation why variables behave the way they do; laws only provide a general summary of the relationship among variables. Theories explain the how and whys about a laws.

Developing TheoriesTheories attempt to explain the fundamental nature of laws. Theories offer abstract

explanations of laws and facts. They try to explain the “why” of laws. Theories involve a more complex understanding (and explanation) of variables than do laws. Examples of theories include Darwin's theory of natural selection and evolution, Einstein's theory of relativity, Canon's theory of emotions, Freud's theory of personality formation and development, and Helmholtz's theories of color vision and hearing.

Theories consist of three aspects:1. Hypothetical construct

Hypothetical constructs represent non-observable abstract entities, consciously invented and generalized for use in theories. For example, the construct of “intelligence” emerged from observations of presumably intelligent and non-intelligent behaviors. “Physical fitness” represents another common construct in areas related to exercise physiology.

2. Associations among constructsScientific inquiry often requires defining relationships among constructs. For example, the construct “physical ability” becomes clarified by its association to the construct “physical fitness,” which itself becomes operationally defined (see below) by numerous specific “fitness” tests. In essence, the meaning of one construct becomes understood through its relationship to other more clearly defined constructs.

Figure 3. Research continuum in science.


3. Operational definitionsThe scientific process requires refinement of constructs into observable characteristics for objective quantification and recording. Operational definitions assign meaning to a construct by clearly outlining the set of operations (like an instruction manual) to measure the quantity of that construct or to manipulate it. For example, the construct intelligence only becomes understood when operationally defined (score on a specific IQ test).

The Surety of ScienceExperimentation represents the scientific mechanism for testing hypothesis; scientists

either reject or fail to reject an hypothesis. Rejecting a hypothesis represents a powerful outcome because it may nullify a theory and specific predictions generated from the theory. Failure to reject an hypothesis indicates that the observable results appear to support the theory. The terms reject and fail to reject (in contrast to prove and disprove) deserve special attention. Failure to reject does not indicate confirmation or proof, only inability to reject an hypothesis. However, if other experiments (particularly from independent laboratories) also fail to reject a given hypothesis, a strong likelihood exists (high probability) of a correct hypothesis. The structure of science makes it impossible to totally confirm a theory's absolute “correctness” because scientists may still devise a future experiment to disprove the theory. The strength of the experimental method lies in rejecting hypotheses that have direct bearing on theories or predictions from theories. The notion of disproof represents an important distinguishing feature of the scientific method.

Publishing Results of ExperimentsFact-finding, law formulation, and theory development represent fundamental aspects of

science. Allowing fellow scientists to critique one’s research findings prior to their distribution completes the process of scientific inquiry. Most journals that disseminate research rely on the researcher’s peers to review and pass judgment on the suitability and quality of methods, experimental design, appropriateness of conclusions, and contribution to new knowledge. While this aspect of science often receives criticism for failing to achieve true objectivity and freedom from professional bias, few would discount its importance; when executed properly, peer review in refereed journals maintains a level of “quality control” in disseminating new information.

Imagine the many instances where an experimental outcome could be influenced by self-interest and/or professional bias. Athletic shoe and nutrient supplement manufacturers sponsor sophisticated laboratories to conduct detailed “research” on the efficacy of their products. To assure credibility, research from such laboratories must be reviewed by experts having no affiliation (direct or indirect) with the company. Without a system of “checks and balances,” such studies should be rightfully viewed with skepticism, and lack trustworthiness as a legitimate source of new knowledge.

Empirical vs. Theoretical – Basic vs. Applied Research

Different approaches lead to successful experimentation and knowledge acquisition. Figure 3 shows two different continuum for experimentation. The theoretical-empirical research continuum has at its foundation experimentation related to establishing laws and testing theories. Scientists in theoretical research


maintain that fact finding alone represents an unfocused waste of energy if the process does not emanate from and contribute to theory building. Scientists at the opposite end of the continuum collect facts and make observations with little regard for building theory. The influential psychologist B.F. Skinner exemplifies the proponent of the empirical research (experience related) approach. His discoveries about reinforcement - a reward for successful behavior increases the probability of success in subsequent trials - were uncovered by “accident.” Skinnerian empiricists argue that theoretical scientists often do not uncover meaningful relationships because they become too “locked into” theoretical formulations and abstract models.

Basic-applied research represents another continuum. Applied research incorporates scientific endeavors to solve specific problems, the solution of which directly applies to medicine, business, the military, sports performance, or society’s general well being. Applied research in exercise physiology might focus on methods for improving training responsiveness, facilitating fluid replenishment and temperature regulation in exercise, enhancing endurance performance, blunting the effects of fatigue by-products, and countering the deterioration of physiologic function during prolonged exposure to a weightless environment.

Basic research lies at the other end of this continuum; no concern exists for immediate practical application of research findings. Instead, the researcher pursues a line of inquire purely for the sake of discovering new knowledge. Often times, uncovering facts that initially seem of little value fill a theoretical void – and like magic, a wonderful new practical solution (or product) emerges. Nowhere has this taken place with more regularity than with research related to the space program. Facts uncovered in a weightless environment about fundamental biological and chemical processes have contributed to practical outcomes that benefit humans. Experiments on how certain chemicals react in zero gravity, for example, have resulted in the discovery of at least 25 new medicines. Manned space missions have provided fresh insights into almost every facet of medicine and physiology, from the affects of weightlessness on bone dynamics, blood pressure, and cardiac, respiratory, hormonal, neural, and muscular function, to growth of genetically engineered plants and a new generation of polymers. Each new insight and observation spawns numerous new ideas and additional facts that help to create products with practical applications.

Research can be generally classified into one of four categories depicted by the quadrants in Figure 6. Basic-empirical research in Quadrant 1 has no immediate practical outcomes and little to do with theory. Research without immediate practical implications, but motivated by theory (establishing laws and conducting experiments that bear on theory), falls into Quadrant 2. Quadrant 3 contains theoretical-applied research primarily focused on problem solving within the framework of an existing theoretical model, while Quadrant 4 classifies empirical-applied research (not theory based), but aimed at solving problems. Often, lines of demarcation are not as clear-cut as in the figure, and a particular research effort might qualify for inclusion in multiple quadrants.


READING #1 STUDY GUIDE

Define Key Terms and Concepts

1. Applied research

2. Basic research

3. Casual relationships

4. Causal relationships

5. Continuous variables

6. Dependent variables

7. Laws

8. Disciplines

9. Discrete variables

10.Empirical research

11.Theories

12.Experimental studies


13.Field of study

14.Field studies

15.Science hierarchy

16.Independent variables

17.Operational definitions

18.Profession

19.Science

20.Theoretical research

STUDY QUESTIONS

The Scientific Method and Exercise PhysiologyGeneral Goals of Science

Give two goals of science.1.2.

Give four aims of science.1. 3.

2. 4.

Hierarchy in ScienceList the three levels of a science.


1.

2.

3.

Fact FindingGive two ways to “find facts”.

1.

2.

Interpreting FactsDescribe an independent variable.

Describe a dependent variable.

Casual and Causal RelationshipsIndependent and Dependent VariablesList two methods to establish cause and effect relationships between independent and dependent variables.

1.

2.

Nature of Experimental StudiesGive the main point of experimental studies.

Nature of Field StudiesGive the main point of field studies.


Establishing LawsExplain a law.

Developing TheoriesList the three aspects of a theory and give one fact about each.

1. 3.

2.

The Surety of ScienceBriefly describe the notion of “disproof.”

Empirical vs. Theoretical – Basic vs. Applied ResearchDescribe differences between empirical v theoretical approaches to knowledge acquisition.

Figure 1. The early Greek influence of Galen’s famous essay, “Exercise With the Small Ball”; a treatise about the many uses of exercise for preventive and therapeutic medical and health benefit. Galen advocated muscle strengthening with rope climbing because it did not pose health problems. He firmly believed in walking and climbing mountains.


READING #2ORIGINS OF EXERCISE PHYSIOLOGY

IntroductionDiscussion of the origins of exercise physiology begins with acknowledgment of the early,

but tremendously influential Greek physicians of antiquity; along the way, we highlight some milestones including many contributions from scholars in the United States and Nordic countries that fostered the scientific assessment of sport and exercise as a respectable field of study.

From Ancient Greece to the United States

Earliest Development – The Age of GalenThe first real focus on the physiology of exercise most likely began in early Greece and Asia

Minor. The topics of exercise, sports, games, and health concerned even earlier civilizations; the Minoan and Mycenaean cultures, the great biblical Empires of David and Solomon, Assyria, Babylonia, Media, and Persia, and the Empires of Alexander. The ancient civilizations of Syria, Egypt, Macedonia, Arabia, Mesopotamia and Persia, India, and China also recorded references to sports, games, and health practices (personal hygiene, exercise, training). The greatest influence on Western Civilization, however, came from the Greek physicians of antiquity - Herodicus (ca. 480 BC); Hippocrates (460-377 BC), and Claudius Galenus or Galen (AD 131-201). Herodicus, a physician and athlete, strongly advocated proper diet in physical training. His early writings and devoted followers influenced Hippocrates, the famous physician and “father of preventive medicine” who contributed 87 treatises on medicine including several on health and hygiene.

Five centuries after Hippocrates, Galen emerged as perhaps the most well-known and influential physician that ever lived. Galen began studying medicine at about age 16. Over the next 50 years he enhanced current thinking about health and scientific hygiene, an area that some might consider applied exercise physiology. Throughout his life, Galen taught and practiced “laws of health” (Table 1).

Laws of health according to Galen, circa A.D. 140

1. Breathe Fresh Air2. Eat Proper Foods3. Drink The Right Beverages4. Exercise5. Get Adequate Sleep6. Have A Daily Bowel Movement7. Control One’s Emotions

Galen produced about 80 treatises and 500 essays on numerous topics related to human anatomy and physiology, nutrition, growth and development, the

Figure 2. Austin Flint


beneficial effects of exercise and deleterious consequences of sedentary living, and diverse diseases and their treatment. One of the first laboratory-oriented physiologists, Galen conducted original experiments in physiology, comparative anatomy, and medicine; he dissected animals (e.g., goats, pigs, cows, horses, and elephants). As physician to the gladiators (probably the first in Sports Medicine), Galen treated torn tendons and muscles using surgical procedures he invented, and recommended rehabilitation therapies and exercise regimens. Galen followed the Hippocratic School of medicine that believed in logical science grounded in observation and experimentation, not superstition or deity dictates.

Galen wrote detailed descriptions about the forms, kinds, and varieties of “swift,” vigorous exercises, including their proper quantity and duration. Galen’s essays about exercise and its effects might be considered the first formal “How To” manuals about such topics that remained influential for the next 15 centuries.

The beginnings of more “modern day” exercise physiology include the periods of Renaissance, Enlightenment, and Scientific Discovery in Europe. During this time, Galen’s ideas impacted the writings of the early physiologists, doctors, and teachers of hygiene and health. For example, in Venice in 1539, the Italian physician Hieronymus Mercurialis (1530-1606) published De arte Gymnastica apud ancientes (The Art of Gymnastics Among the Ancients). This text, heavily influenced by Galen and other Greek and Latin authors, profoundly affected subsequent writings about gymnastics (physical training and exercise) and health (hygiene), in Europe and 19th century America. The panel in Figure 1, redrawn from De arte Gymnastica, acknowledges the early Greek influence of one of Galen’s famous essays, Exercise with the Small Ball, showing his regimen of specific strength exercises that included discus throwing rope climbing.

The Early United States ExperienceBy the early 1800s in the United States, European science-oriented physicians and

experimental anatomists and physiologists strongly promoted ideas about health and hygiene. Prior to 1800, only 39 first-edition American-authored medical books had been published, several medical schools were founded (e.g., Harvard Medical School, 1782), seven medical societies existed (the first was the New Jersey State Medical Society in 1766), and only one medical journal existed (Medical Repository, initially published in 1797). Outside of the United States, 176 medical journals were published; by 1850 the number in the U.S. had increased to 117.

Medical journal publications in the United States increased tremendously during the first half of the nineteenth century. Steady growth in the number of scientific contributions from France and Germany influenced the thinking and practice of American medicine. An explosion of information reached the American public through books, magazines, newspapers, and traveling “health salesmen” who sold an endless variety of tonics and elixirs promising to optimize health and cure disease. Many health reformers and physicians from 1800 to 1850 used “strange” procedures to treat disease and bodily discomforts. To a large extent, scientific knowledge about health and disease was in its infancy. Lack of knowledge and factual information spawned a new generation of “healers” who fostered quackery and primitive

practices on a public thirsting for anything that seemed to work. If a salesman could offer a “cure” to combat gluttony (digestive upset) and other physical ailments, the product would catch hold and become a common remedy.

The “hot topics” of the early 19th century (also true today) included nutrition and dieting (“slimming”), general information about exercise, how to best develop overall fitness, training (gymnastic) exercises for recreation and preparation for sport, and all matters relating to personal health and hygiene. While many health faddists actually practiced “medicine” without a license (licensure was not required to “practice”), some enrolled in newly created medical schools (without entrance requirements), obtaining the

Figure 3. Left; Dr Edward Hitchcock, 1793-1864. Right, Edward Hitchcock, Jr., 1828-1911


M.D. degree in as little as 16 weeks! Despite this brief training, some pioneer physicians contributed in significant ways to medical practice and development of exercise physiology as we know it today.

By the middle 19th century, fledgling medical schools began to graduate their own students, many of whom assumed positions of leadership in academia and allied medical sciences. Interestingly, physicians either taught in medical school and conducted research (and wrote textbooks) or affiliated with departments of physical education and hygiene.

Austin Flint, Jr., M.D.: American Physician-PhysiologistAustin Flint, Jr., M.D. (1836-1915; Figure 2 right), a pioneer American physician-scientist,

contributed significantly to the burgeoning literature in physiology. A respected physician, physiologist, and successful textbook author, he fostered the belief among 19th century American physical education teachers that muscular exercise should be taught from a strong foundation of science and experimentation. Flint, professor of physiology and physiological anatomy in the Bellevue Hospital Medical College of New York, chaired the Department of Physiology and Microbiology from 1861 to 1897. In 1866, he published a series of five classic textbooks, the first entitled The Physiology of Man; Designed to Represent the Existing State of Physiological Science as Applied to the Functions of the Human Body. Vol. 1; Introduction; The Blood; Circulation; Respiration. Eleven years later, Flint published The Principles and Practice of Medicine, a synthesis of his first five textbooks consisting of 987 pages of meticulously organized sections with supporting documentation. Dr. Flint, well trained in the scientific method, received the American Medical Association’s prize for basic research on the heart in 1858. He published his medical school thesis, “The phenomena of capillary circulation,” in an 1878 issue of the American Journal of the Medical Sciences. His 1877 textbook included many exercise-related details about: (1) Influence of posture and exercise on pulse rate; (2) Influence of muscular activity on respiration; and (3) Influence of muscular exercise on nitrogen elimination.

Flint was well aware of scientific experimentation in France and England, and cited the experimental works of leading European physiologists and physicians including the incomparable François Magendie (1783-1855), Claude Bernard (1813-1878), and influential German physiologists Justis von Liebig (1803-1873), Edward Pflüger (1829-1910), and Carl von Voit (1831-1908). He also discussed the important contributions to metabolism of Antoine Lavoisier (1743-1784) and digestive physiology from American physician-physiologist William Beaumont (1785-1853).

Through his textbooks, Austin Flint, Jr. influenced the first medically trained and science-oriented professor of physical education, Edward Hitchcock, Jr., M.D. (see next section). Hitchcock quoted Flint about the muscular system in his syllabus of Health Lectures, which became required reading for all students enrolled at Amherst College between 1861 and 1905.

Amherst College ConnectionTwo physicians, father and son (Figure 3) pioneered the

American sports science movement (Figure 4). Edward Hitchcock, D.D., LL.D. (1793-1864), served as professor of chemistry and natural history at Amherst College and as president of the College from 1845-1854. He convinced the college president in 1861 to allow his son Edward [(1828-1911; Amherst undergraduate (1849); Harvard medical degree (1853)] to assume the duties of his anatomy course. On August 15, 1861 Edward Hitchcock, Jr. became Professor of Hygiene and Physical Education with full academic rank in the Department of Physical Culture at an annual salary of $1,000 - a position he held almost

continuously to 1911. Hitchcock’s professorship became the second such appointment in

Figure 4. G.W. Fitz


physical education in an American college. The first, to John D. Hooker a year earlier at Amherst College in 1860, was short lived due to Hooker’s poor health. Hooker resigned in 1861 with Hitchcock appointed in his place.

William Augustus Stearns, D.D., the fourth President of Amherst College had proposed the original idea of a Department of Physical Education with a professorship in 1854. Stearns considered physical education instruction essential for the health of students and useful to prepare them physically, spiritually, and intellectually. In 1860, the Barrett Gymnasium at Amherst College, was completed and served as the training facility where all students were required to perform systematic exercises for 30 minutes daily, four days a week A unique feature of the gymnasium included Dr. Hitchcock’s scientific laboratory that included strength and anthropometric equipment, and a spirometer to measure lung function, which he used to measure the vital statistics of all Amherst students. Dr. Hitchcock was first to statistically record basic data on a large group of subjects on a yearly basis. These measurements provided Dr. Hitchcock with solid information for his counseling duties concerning health, hygiene, and exercise training.

In 1860, the Hitchcock’s co-authored an anatomy and physiology textbook geared to college physical education (Hitchcock, E., and Hitchcock, E., Jr.: Elementary Anatomy and Physiology for Colleges, Academies, and Other Schools. New York, Ivison, Phinney & Co., 1860); 29 years earlier, the father had published a science-oriented hygiene textbook. Interestingly, the anatomy and physiology book predated Flint’s similar text by six years, illustrating that an American-trained physician, with strong allegiance to the implementation of health and hygiene in the curriculum, helped set the stage for the study of exercise and training well before the medical establishment focused on this aspect of the discipline. A pedagogical aspect of the Hitchcocks' text included questions at the bottom of each page about topics under consideration. In essence, the textbook also served as a “study guide” or “workbook.”

George Wells Fitz, M.D.: A Major InfluenceGeorge Wells Fitz, M.D. (1860-1934), early “exercise physiology”

researcher helped create the Department of Anatomy, Physiology, and Physical Training at Harvard University in 1891. One year later, Fitz established the first formal exercise physiology laboratory. Instructors in the initial undergraduate B.S. degree program included distinguished Harvard Medical School physiologists Henry Pickering Bowditch whose research produced the “all or none principle of cardiac contraction” and “treppe” (staircase phenomenon of muscle contraction), and W. T. Porter, internationally recognized physiologist. Both men were noted for their rigorous scientific and laboratory training. The new major, grounded in the basic sciences, included formal coursework in exercise physiology, zoology, morphology (animal and human), applied anatomy, anthropometry, animal mechanics, medical chemistry, comparative

anatomy, remedial exercises, physics, gymnastics and athletics, history of physical education, and English (see accompanying For Your Information, below)

FOR YOUR INFORMATIONExercise PhysiologyFew of today’s undergraduate Physical Education [Kinesiology] major programs could match the strong science core required at Harvard in 1893. Below is listed the 4-year course of study. Along with core courses, Professor Fitz established an exercise physiology laboratory [Reference: Harvard University Catalog: Lawrence Scientific School. Description of Course of Study. 1891-1892, page 222.]

Course of Study: Department of Anatomy, Physiology, and Physical Training, Lawrence


Scientific School, Harvard University, 1893.First Year

Experimental Physics

Elementary Zoology

Morphology of Animals

Morphology of Plants

Elementary Physiology and Hygiene

General Chemistry

Rhetoric and English Composition

Elementary German

Gymnastics and Athletics

Second YearComparative Anatomy of VertebratesGeologyPhysical Geography and MeteorologyExperimental PhysicsGeneral Descriptive PhysicsQualitative AnalysisEnglish CompositionGymnastics and Athletics

Third Year (at Harvard Medical)

Anatomy and DissectionGeneral PhysiologyHistologyHygieneFoods and CookingMedical ChemistryAuscultation and PercussionGymnastics and Athletics

Fourth YearPsychologyAnthropometryApplied Anatomy and Animal Mechanics (Kinesiology)Physiology of ExerciseRemedial ExerciseHistory of Physical EducationForensicsGymnastics and Athletics

Prelude to Exercise Science: Harvard’s Department of Anatomy, Physiology, and Physical Training (B.S. Degree, 1891-1898)

Harvard’s physical education major and exercise physiology research laboratory focused on three objectives:

Prepare students, with or without subsequent training in medicine, to become directors of gymnasia or instructors in physical training

Provide necessary knowledge about the science of exercise Provide suitable academic preparation to enter Medical SchoolPhysical education students took general anatomy and physiology courses in the medical

school; after four years of study, graduates could enroll as second-year medical students and graduate in three years with an M.D. degree. Dr. Fitz taught the physiology of exercise course; thus, he may have been the first person to formally teach such a course. It included experimental investigation and original work and thesis, including six hours a week of laboratory study. The prerequisite for the “Physiology of Exercise” course included a course in general physiology at the medical school or its equivalent. The course introduced students to the fundamentals of physical education, and provided training in experimental methods related to exercise physiology.

In addition to a remedial exercise course, students took a required course in “Applied Anatomy and Animal Mechanics. Action of Muscles in different Exercises.” This thrice-weekly course taught by Dr. Dudley Sergeant, was the forerunner of modern biomechanics courses. Its prerequisite was general anatomy at the medical school, or its equivalent.

Nine men graduated with B.S. degrees from the Department of Anatomy, Physiology, and Physical Training, before it’s dismantling in 1900. The aim of the major was to prepare students to become directors of gymnasia or instructors in physical training, to provide students with the necessary knowledge about the science of exercise, and to offer suitable training for entrance to medical school. The stated purpose of the new exercise physiology research laboratory was as follows:

A large and well-equipped laboratory has been organized for the experimental study of the physiology of exercise. The object of this work is


to exemplify the hygiene of the muscles, the conditions under which they act, the relation of their action to the body as a whole affecting blood supply and general hygienic conditions, and the effects of various exercises upon muscular growth and general health.

Coinciding with Fitz’s untimely departure from Harvard in 1899 (no one is quite sure why Fits left Harvard), the department changed its curricular emphasis (the term physical training was dropped from the department title), thus terminating at least temporarily this unique experiment in higher education, and depriving the next generation of students in exercise physiology of a visionary to propel the field forward.

One of the legacies of the Fitz-directed “Harvard experience” between 1891 and 1899 was the mentoring it provided specialists who began their careers with a strong scientific basis in exercise and training and its relationship to health. They were taught that experimentation and discovery of new knowledge about exercise and training played a crucial role in furthering development of a science based curriculum. Unfortunately, it would take another six decades before the next generation of science-oriented physical educators (led by physiologists like A.V. Hill and D.B. Dill, not educators) would once again exert strong influence on physical education and propel exercise physiology to the forefront of scientific investigation.

By 1927, 135 institutions in the U.S. offered bachelors degree programs in Physical Education with coursework in the basic sciences; this included four masters degree programs and two doctoral programs (Teachers College-Columbia University and New York University). Since then, programs of study [with emphasis in exercise physiology] have proliferated. Currently, about 172 programs in the United States and 19 in Canada offer the masters or doctoral degrees with specialization in some aspect of exercise physiology.

Exercise Studies in Research JournalsA notable event in the growth of exercise physiology occurred in 1898 when three articles

on physical activity appeared in the first volume of the American Journal of Physiology. Other articles and reviews subsequently appeared in prestigious journals, including the first published review in Physiological Reviews (2: 310, 1922) on the mechanisms of muscular contraction by Nobel laureate A.V. Hill. The German applied physiology publication, Internationale Zeitschrift fur angewandte Physiologie einschliesslich Arbeitsphysiologie (1929-1940; now European Journal of Applied Physiology and Occupational Physiology), became a significant journal for research about exercise physiology-related topics. The Journal of Applied Physiology, first published in 1948 is a must reading for exercise physiologists. The official journal of the American College of Sports Medicine, Medicine and Science in Sports, first appeared in 1969. It aimed to integrate both medical and physiological aspects of the emerging fields of sports medicine and exercise science. The official name of this journal changed in 1980 to Medicine and Science in Sports and Exercise. Publications emphasizing applied and basic exercise physiology research have increased as the field expands into different areas. The World Wide Web offers unique growth potential in this regard.

Figure 5. David Bruce Dill (1891-1986)


The Harvard Fatigue Laboratory (1927-1946)The real impact of laboratory research in exercise physiology (along with many other research specialties) occurred in 1927, again at Harvard University, 27 years after Harvard closed the first exercise physiology laboratory in the United States. The 800-square foot Harvard Fatigue Laboratory in the basement of Morgan Hall of Harvard University’s Business School established the legitimacy of exercise physiology on its own merits as an important area of research and study. Many of the great scientists of the 20th century with an interest in exercise affiliated with the Fatigue Laboratory. Established by renowned Harvard

chemist and professor of biochemistry, J. Henderson, M.D. (1878-1942). David Bruce Dill (1891-1986), a Stanford Ph.D. in physical chemistry became the first and only scientific director of the Laboratory. While at Harvard, Dill refocused his efforts from biochemistry to experimental

physiology and became the driving force behind the Laboratory’s numerous scientific accomplishments.

Similar to the legacy of the first exercise physiology laboratory established in 1891 at Harvard’s Lawrence Scientific School 31 years earlier, the Harvard Fatigue Laboratory demanded excellence in research and scholarship. Cooperation among scientists from around the world fostered lasting collaborations. Many its charter scientists profoundly influenced a

new generation of exercise physiologists worldwide.

Other Early Exercise Physiology Research LaboratoriesOther notable research laboratories helped exercise physiology become an established field

of study at colleges and universities. These included the Nutrition Laboratory at the Carnegie Institute in Washington, D.C. (established 1904) that initiated experiments in nutrition and energy metabolism. The first research laboratories established in a department of physical education in the United States originated at George Williams College (1923), University of Illinois (1925), Springfield College (1927), and Laboratory of Physiological Hygiene at the University of California, Berkeley (1934). The syllabus for the Physiological Hygiene course contained 12 laboratory experiments. In 1936, Dr. Franklin M. Henry assumed responsibility for the laboratory; shortly thereafter, his research appeared in various physiology-oriented journals.

FOR YOUR INFORMATIONThe Harvard Fatigue LaboratoryOver a 20-year span, Harvard Fatigue Laboratory scientists published 352 research papers, monographs, and a book dealing with basic and applied exercise physiology, including methodological refinements in blood chemistry analysis, and methods for analyzing fractional concentrations of expired air. Other research included acute responses and chronic adaptations to exercise under the environmental stress of altitude, heat, and cold exposure. Most of the experiments used humans exercising on a treadmill or bicycle ergometer. These studies formed the cornerstone for future research efforts in exercise physiology; they included assessment of working capacity and physical fitness, cardiovascular and hemodynamic responses during maximal exercise, oxygen uptake and substrate utilization kinetics, exercise and recovery metabolism.

Figure 7. Per-Olof Astrand, Stockholm, Sweden.

Figure 6. The “three musketeers”; Dr. Erling Assmusen (left), Erik Hohwu-Christensed (center), and Marius Nielson (right), 1988.


Nordic Connection (Denmark, Sweden, Norway and Finland)Denmark and Sweden played an important historical role in developing the field of exercise

physiology. In 1800, Denmark became the first European country to require physical training (military-style gymnastics) in the school curriculum. Since then, the Danish and Swedish scientists continue to make outstanding contributions to research in both traditional physiology and exercise physiology.

Danish InfluenceIn 1909, the University of

Copenhagen endowed the equivalent of a Chair in Anatomy, Physiology, and Theory of Gymnastics. The first Docent, Johannes Lindhard, M.D. (1870-1947), later teamed with August Krogh, Ph.D. (1874-1949), an eminent scientist specializing in physiological chemistry and research instrument design and construction, to conduct many of the classic experiments in exercise physiology.

By 1910, Krogh and his physician-wife Marie had proven through a series

of ingenious, experiments that diffusion governed pulmonary gas exchange during exercise and altitude exposure, not oxygen secretion from lung tissue into the blood as postulated by British physiologists Sir John Scott Haldane and James Priestley. Krogh won the Nobel Prize in Physiology or Medicine in 1920 for discovering the mechanism for capillary control of blood flow in resting and exercising muscle. To honor Krogh’s achievements the institute for physiological research in Copenhagen bears his name (August Krogh Institute).

Three other Danish researchers - physiologists Erling Asmussen (1907-1991; ACSM Citation Award, 1976 and ACSM Honor Award, 1979), Erik Hohwü-Christensen (b. 1904-1996; ACSM Honor Award, 1981), and Marius Nielsen (b. 1903) - conducted significant exercise physiology studies (Figure 6, above). These “three musketeers,” as Krogh called them, published voluminously during the 1930s to 1970s.

Swedish InfluenceModern exercise physiology in Sweden can be traced to Per Henrik

Ling (1776-1839), who in 1813 became the first director of Stockholm’s Royal Central Institute of Gymnastics. Ling, a specialist in fencing, developed a system (incorporating his studies of anatomy and physiology) of “medical gymnastics,” which became part of Sweden’s school curriculum in 1820. Ling’s son, Hjalmar, published a book on the kinesiology of body movements in 1866. As a result of the Lings’ philosophy and influence, physical education graduates from the

Stockholm Central Institute were well schooled in the basic biological sciences, in addition to proficiency in sports and games. Currently, the College of Physical Education (Gymnastik-Och Idrotts-skolan) and the Department of Physiology in the Karolinska Institute Medical School in

Stockholm continue to sponsor studies in exercise physiology. Per-Olof Åstrand, M.D., Ph.D. (b. 1922) is the most famous graduate of the College of

Physical Education (1946); in 1952 he presented his doctoral thesis at the Karolinska Institute Medical School (Figure 7) Åstrand taught in the Department of Physiology in the College of Physical Education from 1946-1977; it then became a department at the Karolinska Institute

Figure 7. Barbour (Women’s) Gym [circa, 1900] attached to Waterman (Men’s) gym (not shown [circa 1894] on the site of the current chemistry building. Barbour/ Waterman was the long time home of Kinesiology. It was demolished in 1977.


where he served as professor and department head from 1977 to 1987. Christensen, Åstrand’s mentor, supervised his thesis, which evaluated physical working capacity of men and women aged 4 to 33 years. This important study, among others, established a line of research that propelled Åstrand to the forefront of experimental exercise physiology for which he achieved worldwide fame. Four of his papers, published in 1960 with Christensen as co-author, stimulated further studies on the physiological responses to intermittent exercise. Åstrand has mentored an impressive group of exercise physiologists, including “superstar” Bengt Saltin.

Norwegian and Finnish InfluenceThe new generation of exercise physiologists trained in the late 1940s analyzed respiratory

gases with a highly accurate sampling apparatus that measured minute quantities of CO2 and O2 in expired air. Norwegian scientist Per Scholander (1905-1980) developed the method of analysis and analyzer in 1947. Another prominent Norwegian researcher, Lars A. Hermansen (1933-1984; ACSM Citation Award, 1985) made many contributions including a classic 1969 article entitled “Anaerobic energy release,” that appeared in the first issue of the ACSM journal, Medicine and Science in Sports).

In Finland, Martti Karvonen, M.D., Ph.D. (ACSM Honor Award, 1991) from the Physiology Department of the Institute of Occupational Health, Helsinki, achieved notoriety for a method to predict optimal exercise training heart rate, now called the “Karvonen formula”. Paavo Komi, Department of Physical Activity, University of Jyvaskyla, has been Finland’s most prolific researcher with numerous experiments published in the combined areas of exercise physiology and sport biomechanics.

The University of Michigan ExperienceIn 1870 the University of

Michigan Senate recommended the establishment of a Department of Hygiene and Physical Culture, the appointment of a professor to run it, and the construction of a gymnasium costing about $25,000. No action was taken on these recommendations, but the seed were sewn. Nearly 25 years later the gymnasium and the program became a reality. The roots of today’s Kinesiology program date

back earlier than the Senate’s 1870 statement and the 1894 completion of Waterman gym (150 feet long and 90 feet wide with a running track in the balcony of 14 laps to the mile was located on the site of Chemistry building, but razed in 1977). Students formed the first gymnasium in 1858 from an old military barracks on the site of the original Engineering building on the Diag. This makeshift facility rested on poles, open to weather, and was furnished only with a few ropes and rings. Students made various attempts at fundraising to build a “proper” gym, but most of the money ($20,000) came from Joshua W. Waterman, a Detroit attorney and sports enthusiast. The university added the rest and Waterman Gym were completed at a cost of $51,874.49. The gym opened in 1894 and Dr. James Fitzgerald was named the first director. Dr. George A. May, hired in 1901 to teach classes served as director


of the gym from 1910 to 1942. “Doc” May was a well-known personality on campus and was instrumental in convincing the university senate to offer physical education instruction on a required bases to all students (men and women) to “counteract the strain placed on students by extensive study”. Women were permitted to use Waterman gym, “on occasion during mornings”. University President Dr. James Angell supported coeducational instruction, including use of the gym, and authorized the building of Barbour Gymnasium (Regent Levi Barbour offered the land adjacent to Waterman Gym valued at $25,000) in 1894 (full use occurred in 1896.) President Angell, seeing the need for a women’s physical education program hired Dr. Eliza M. Mosher, a UM medical student in the early ‘70s and a practicing physician in New York, to become the first Professor of Hygiene and Women’s Dean of the Department of Literature, Science and Arts (becoming the first women to head Physical Education for women.)

In 1894 men’ and women’s physical education began as electives, but four years later the Regents passed a resolution making the classes compulsory for all freshman (in the hope that the students would continue to take systematic exercise on a regular basis thereafter). By this time Physical Education was an integral part of campus life, but a professional four-year program to train teachers in physical education, leading to a B.S. degree would not be started until the early 1920s.

In March, 1920, University President Marion L. Burton brought before the UM Regents message from the Michigan State Department of Public Instruction on the growing need for physical education teachers. The following February, the Regents took the following action:

“There is herby created and established a University Department of Physical Education….“The Director of Physical Education shall be in primary charge of all athletic fields for men and women, of both gymnasium, of all sports, indoor, outdoor, intercollegiate and intramural.”

In June, the plan was revised to create two units: A Department of Intercollegiate Athletics, headed by Fielding Yost, and a Department of Hygiene and Public Health, including Physical Education. Dr. John M. Sudwall was named to the latter post in September, 1921. Physical Education was placed in the newly formed School of Education. With no budget for new faculty, the four-year curriculum was inaugurated in fall, 1921. It was designed to prepare men and women to:

Supervise the physical health of children in the public schools Provide recreation for growing youth Instruct prospective coaches in scientific methods and training of teams

The program emphasized two areas: training individuals in gymnastics, recreation, health and games for people of all ages; and prepare future coaches in various sports.

Among the many faculty whose contributions shaped the Men’s and Women’s programs through and beyond the 20s, two deserve special mention: Margaret Bell, who chaired the Women’s Physical Education Department, 1923-1957, and Elmer Mitchell, Director of Intramural Sports from 1919-1958, and Chair of the Department of Physical Education for Men, 1942-1958.

With the beginning of the program in 1921, the departments essentially had two parts: the required program that provided non-credit physical education (sports and games) courses for all students, and the four-year professional program leading to teacher certification.

With the undergraduate program well established by the 1930s, the PE faculty introduced a graduate curriculum in Physical Education leading to an M.A. degree in 1931 (there were 3 areas of specialization: administration, supervision and teaching; school health education, and teacher education). The Ph.D. or Ed.D. was established in 1938, and first two doctoral degrees


were awarded in 1940. By the end of the 1930s, undergraduate enrollment in Physical Education stood at about 75 men and 50 women.

In 1941, the Physical Education Departments (men’s and women’s) were reorganized and renamed Physical Education and Athletics, and by 1942 all academic titles (professor, associate professor, assistant professor) were taken away and changed to director, associate supervisor, assistant supervisor. The departments were removed from education and stood as a solitary unit on campus, yet were permitted to continue to grant university degrees and offer required physical training classes.

In 1949 Paul Hunsicker, a recent graduate of T.K. Cureton’s Illinois program in Physical Education (emphasis in Exercise Physiology) came to Michigan and established the first experimental exercise physiology laboratory (housed in the old Physical Education Building – now the Athletic Ticket Office on South State Street). Dr. Hunsicker established the laboratory with a primary interest in physical fitness testing of youth throughout the country.

Upon the retirement of Dr. Mitchell in 1958, Dr. Hunsicker became head of the Men’s Department of Physical Education. Dr. Esther French succeeded Margaret Bell as Chair of the Women’s Physical Education Department in 1957. In 1967 the University reversed its stance of 25 years earlier and returned the professorial titles to the men’s and women’s faculties, following an academic review.

In 1970 the Physical Education requirement was abolished. Thus, the 72-year tradition of required Physical Education was ended; in its place, a coeducational elective program continued to offer students the opportunity to acquire sports sills. This elective program has evolved into today’s Adult Lifestyle Program.

In 1971 the Men’s and Women’s Departments were merged, with Dr. Paul Hunsicker serving as Chair. At the height of his career, in January, 1976, Paul Hunsicker died of a heart attack. Dr. D.W. Edington, a professor from the University of Massachusetts was recruited as chair with the mandate to establish a first-rate research department. During the mid ‘70s Physical Education severed ties with Athletics to become an independent unit within the School of Education. The undergraduate and graduate programs focused on research with little emphasis on teacher preparation. New faculty was recruited with emphasis in motor control, biomechanics and exercise physiology and new laboratories were established.

On September 21, 1984 the UM Regents created an independent Division of Physical Education, completely separated from Education. On July 20, 1990 the Michigan Board of Regents agreed that Physical Education no longer accurately described the field of study and officially changed the name to the Division of Kinesiology. Kinesiology is now one of the 17 schools and colleges within the university.

Other Contributors to Exercise PhysiologyIn addition to the American and Nordic scientists who achieved distinction in the study of

exercise, many other “giants” in the fields of physiology and experimental science made monumental contributions that indirectly contributed to the knowledge base in exercise physiology. These include physiologists Antoine Laurent Lavoisier (1743-1794; fuel combustion), Sir Joseph Barcroft (1872-1947; altitude), Christian Bohr (1855-1911; oxygen-hemoglobin dissociation curve), John Scott Haldane (1860-1936; respiration), Otto Myerhoff, 1884-1951; Nobel Prize, cellular metabolic pathways), Nathan Zuntz (1847-1920; portable metabolism apparatus), Carl von Voit (1831-1908) and his student, Max Rubner (1854-1932; direct and indirect calorimetry, and specific dynamic action of food), Max von Pettenkofer (1818-1901; nutrient metabolism), Eduard F.W. Pflüger (1829-1910; tissue oxidation).

Closer to home, the field of exercise physiology owes a debt of gratitude to the pioneers of the physical fitness movement in the United States, notably Thomas K. Cureton (1901-1993; ACSM charter member, 1969 ACSM Honor Award) at the University of Illinois, Champaign. Cureton, a prolific researcher, trained four generations of students beginning in 1941 who later established their own research programs and influenced many of today's top exercise


physiologists. These early graduates with an exercise physiology specialty soon assumed leadership positions as professors of physical education with teaching and research responsibilities in exercise physiology at numerous colleges and universities in the United States and throughout the world.


Reading #2 Study Guide

Define Key Terms and Concepts1. Archibald Vivian Hill

2. August Krogh

3. Austin Flint, Jr., M.D.

4. D.W. Edington

5. David Bruce Dill

6. Eliza M. Mosher

7. Fielding Yost

8. Galen

9. George Wells Fitz.

10. Harvard Fatigue Laboratory

11. Hippocrates

12. Margaret Bell

13. Paul Hunsicker


14. Per-Olof Åstrand

15. The Hitchcock’s

16. Thomas K. Cureton

STUDY QUESTIONS

From Ancient Greece to the United States, circa 1850Earliest DevelopmentName of the Greek physician-athlete who many consider the “father of preventive medicine.

The Early United States Experience Name the first US medical school.

List two “hot” topics of interest to medicine and exercise physiology in the early 19th century.

1.

2.

Austin Flint, Jr., M.D.: American Physician-PhysiologistGive two reasons for Austin Flint’s importance in the history of exercise physiology.

1.

2.

Amherst College ConnectionName the father and son pioneer sport science professors.

1.

2.

George Wells Fitz, M.D.: A Major Influence


List two reasons for G.W. Fitz importance in the history of exercise physiology.1.

2.

Prelude to Exercise Science: Harvard’s Department of Anatomy, Physiology, and Physical Training (B.S. Degree, 1891-1898)List one unique aspect of the academic major in Harvard’s Department of Anatomy, Physiology, and Physical Training.

List three objectives of Harvard’s new physical education major and exercise physiology research laboratory.

1. 3.

2.

The Harvard Fatigue Laboratory (1927-1946)Name the first director of the Harvard Fatigue Laboratory.

Other Early Exercise Physiology Research LaboratoriesName an “exercise physiology” department in the United States before 1935.

The Nordic Connection (Denmark, Sweden, Norway and Finland)Which of the Nordic countries first required physical training in the school curriculum?

Danish InfluenceName one famous Danish exercise physiologist.

Swedish InfluenceName one famous Swedish exercise physiologist.

Norwegian and Finnish InfluenceName one famous Norwegian exercise physiologist.


Other Contributors to Exercise Physiology KnowledgeName the most famous “physical fitness” researcher from the U.S.

The University of Michigan ExperienceGive four important dates and their significance in the development of the Division of Kinesiology at the University of Michigan.

Date Significance1.

2.

3.

4.

Name four important people and briefly describe their contributions to shaping the history of the Division of Kinesiology at the University of Michigan.

1. 3.

2. 4.


READING #3PROFESSIONAL EXERCISE PHYSIOLOGY

Introduction: The Exercise PhysiologistMany individuals view exercise physiology as representing an undergraduate or graduate

academic major (or concentration) completed at an accredited college or university. In this regard, only those who complete this academic major have the “right” to be called “exercise physiologist.” However, many individuals complete undergraduate and graduate degrees in related fields with considerable coursework and practical experience in exercise physiology (or related areas). Consequently, the title exercise physiologist could also apply so long as their academic preparation is adequate. Resolution of this dilemma becomes difficult because no national consensus exists as to what constitutes an acceptable (or minimal) academic program of course work in exercise physiology. In addition, there are no universal standards for hands-on laboratory experiences (anatomy, kinesiology, biomechanics, and exercise physiology), demonstrated level of competency, and internship hours that would stand the test of national certification or licensure. Moreover, with areas of concentration within the field are so broad, consensus certification testing indeed becomes challenging.

No national accreditation or licensure exists to certify exercise physiologists. Only one state, Louisiana, currently requires individuals to pass a state certification exam for the position of “clinical exercise physiologist.” Many states are in various stages of similar legislation.

What Do Exercise Physiologists Do?Exercise physiologists assume diverse careers. Some use their research skills in colleges,

universities, and private industry settings. Others are employed in health, fitness, and rehabilitation centers, while others serve as educators, personal trainers, managers, and entrepreneurs in the health/fitness industry.

Exercise physiologists also own health and fitness companies or are hands-on practitioners who teach and service the community including corporate, industrial, and governmental agencies. Some specialize in other types of professional work like massage therapy while others go on to pursue professional degrees in physical therapy, occupational therapy, nursing, nutrition, medicine, and chiropractic.

Table 1 presents a partial list of different employment descriptions for a qualified exercise physiologist in one of six areas.Table 1. Partial list of different employment opportunities for qualified exercise

physiologists.

Sports College/Universit

y Communit

y Clinical Gov/Military

Business Private

Sports director Professor

Manage/direct health/wellness programs

Test/supervise cardiopulmonary patients

Fitness director/man-ager

Sports manage-ment

Personal health/fitness consultant

Strength/con-ditioning coach

Researcher Community education

Evaluate/supervise special populations (diabetes; obesity; arthritis; dyslipi-demia; cystic fibro-sis; cancer, hyper-tension; children;

Health/fit-ness directory in correctional institutions

Health/fit-ness promotion

Own business


low functional capa-city; pregnancy)

Director, manager of state/national teams

Administrator

Exercise technologies in cardiology practice

Sport psycholo-gist

Consultant TeacherInstructor

Occupational rehabilitation

Sports nutrition programs

ResearcherHealth/fit-ness club instructor

The Exercise Physiologist/Health-Fitness Professional in the Clinical Setting

The well-documented health benefits of regular physical activity have enhanced the exercise physiologist’s role beyond traditional lines. A clinical exercise physiologist becomes part of the health/fitness professional team. This team approach to preventive and rehabilitative services requires different personnel depending on program mission, population served, location, number of participants, space availability, and funding level. A comprehensive clinical program can include the following personnel, in addition to the exercise physiologist:

Physicians Dietitians Nurses Physical therapists Occupational

therapists Social workers

Respiratory therapists

Psychologists

Health educators Certified personnel (exercise leaders, health-fitness instructors, directors, exercise test technologists, preventive and rehabilitative exercise specialists, preventive and rehabilitative exercise directors)

The health professional team works in harmony to restore a patient’s mobility, functional capacity, and overall health. Issues about available funding, specific client needs, and programmatic direction dictate the extent of part-time and full-time personnel.


Sports Medicine and Exercise Physiology: A Vital LinkThe traditional view of sports medicine involves rehabilitating athletes from sports injuries.

A more contemporary view relates sports medicine to the scientific and medical aspects of physical activity, physical fitness, and sports. Thus, a close link ties sports medicine to clinical exercise physiology. The sports medicine professional and exercise physiologist work hand-in-hand with similar populations including the sedentary person, the athlete and those requiring special needs (e.g., disabled athlete).

Carefully prescribed exercise contributes to overall health and quality of life. In conjunction with sports medicine professionals, the clinical exercise physiologist tests, treats, and rehabilitates individuals with diverse diseases and disabilities. In addition, prescription of physical activity and athletic competition for the physically challenged plays an important role in sports medicine and exercise physiology, providing unique opportunities for research, clinical and professional advancement.

Training and Certification by Professional OrganizationsTo fulfill responsibilities in the exercise setting, the health-fitness professional integrates

unique knowledge, skills, and abilities related to exercise, physical fitness, and health. Different professional organizations provide leadership in training and certifying health-fitness professionals. Table 2 lists organizations offering training/certification programs with diverse emphases and specializations.

Table 2. Organizations offering training/certification programs related to physical activity.Organization Areas of Specialization and

CertificationAerobics and Fitness Association of AFP Fitness Practitioner, Primary Aerobics

FOR YOUR INFORMATIONPartial Listing of Research Journals publishing exercise physiology research articles.Biomedical Databases Exercise Immunology ReviewBritish Journal of Sports Medicine Health Sciences LibraryBritish Medical Journal Human PerformanceCanadian Journal of Applied Physiology International Journal of PsychophysiologyClinical Exercise Physiology International Journal of Sport NutritionCoaching Science Abstracts Journal of Applied BiomechanicsHuman Movement Science Journal of Aging and Physical ActivityInternational Journal of Epidemiology Journal of Applied PhysiologyInternet Journal of Health Promotion Journal of Health CommunicationJournal of the American Medical Association Motor ControlJournal of Applied Biomechanics Journal of Sport ManagementJournal of Exercise Physiology online Journal of Sport RehabilitationJournal of Performance Enhancement Journal of Sport and Exercise PsychologyJournal of Science and Medicine in Sport Kinesiology OnlineJournal of Athletic Training Pediatric Exercise ScienceMedicine & Science in Sports & Exercise New Zealand Journal of Physiotherapy


America (AFAA) 15250 Ventura Blvd., Suite 200 Sherman Oaks, CA 91403

Instructor, Personal Trainer & Fitness Counselor, Step Reebok Certification, Weight Room/Resistance Training Certification, Emergency Response Certification

American College Sports Medicine (ACSM) 401 West Michigan Street Indianapolis, IN 46202

Exercise Leader, Health/Fitness Instructor, Exercise Test Technologist, Health/Fitness Director, Exercise Specialist, Program Director

American Council on Exercise (ACE) 5820 Oberlin Drive, Suite 102 San Diego, CA 92121

Group Fitness Instructor, Personal Trainer, Lifestyle & Weight Management Consultant

Canadian Aerobics Instructors Network (CAIN) 2441 Lakeshore Road West, P.O. Box 70029 Oakville, ON L6L 6M9

CIAI Instructor, Certified Personal Trainer

Canadian Personal Trainers Network (CPTN) Ontario Fitness Council (OFC) 1185 Eglington Ave. East, Suite 407 North York, ON M3C 3C6

CPTN/OFC Certified Personal Trainer, CPTN Certified Specialty Personal Trainer, CPTN/OFC Assessor of Personal Trainers, CPTN/OFC Course Conductor for Personal Trainers

Canadian Society for Exercise Physiology1600 James Naismith Drive, Suite 311 Gloucester, ON K1B 5N4

CFC-Certified Fitness Consultant, PFLC-Professional Fitness and Lifestyle Consultant, AFAC-Accredited Fitness Appraisal Center

The Cooper Institute for Aerobics Research 12330 Preston Road Dallas, TX 75230

PFS-Physical Fitness Specialists (Personal Trainer), GEL-Group Exercise Leadership (Aerobic Instructor), ADV.PFS-Advanced Physical Fitness Specialist, Biomechanics of Strength Training, Health Promotion Director

Disabled Sports USA 451 Hungerford Drive, Suite 100 Rockville, MD 20850

Adapted Fitness Instructor

International Weightlifting Association (IWA) P.O. Box 444 Hudson, OH 44236

CWT-Certified Weight Trainer

Jazzercise 2808 Roosevelt Blvd. Carlsbad, CA 92008

Certified Jazzercise Instructor

National Federation of Personal Trainers (NFPT) P.O. Box 4579 Lafayette, IN, 47903

Certified Personal Fitness Trainer

National Strength & Conditioning Association (NSCA) P.O. Box 38909 Colorado Springs, CO 80937

Certified Strength and Conditioning Specialist, Certified Personal Trainer

YMCA of the USA 101 North Wacker Drive Chicago, IL 60606

Certified Fitness Leader (Stage I-Theory, II-Applied Theory, III-Practical, Certified Specialty Leader, Trainer of Fitness Leaders, Trainer of Trainers

The American College of Sports Medicine (ACSM) has emerged as the preeminent academic organization offering comprehensive programs in areas related to the health-fitness profession. ACSM certifications encompass cognitive and practical competencies that are evaluated by written and practical examinations. The candidate must successfully complete each of these components (scored separately) to receive the world-recognized ACSM certification. ACSM offers a wide variety of certification programs throughout the United States and in other countries <http://www.acsm.org/index.asp>.

ACSM Qualifications and Certifications

http://www.acsm.org/index.asp


Health and fitness professionals need to be knowledgeable and competent in different areas, including first-aid and CPR certification, depending on personal interest. Table 3 presents content areas for different ACSM certifications. Each of these areas has general and specific learning objectives.

Table 3. Major knowledge/competency areas required for individuals interested in ACSM certifications

Functional anatomy and biomechanics

Exercise physiology

Pathophysiology and risk factors

Human development and aging

Human behavior and psychology

Health appraisal and fitness testing

ECG

Emergency procedures and safety

Exercise programming

Program administrationFrom ACSM’s Guidelines for Exercise Testing and Prescription, 5th Ed. Baltimore, MD: Williams & Wilkins, 1995.

Health and Fitness TrackThe Health and Fitness Track encompasses the Exercise Leader, Health/Fitness

Instructor, and Health/Fitness Director categories.Exercise Leader

An Exercise Leader must know about physical fitness (including basic motivation and counseling techniques) for healthy individuals and those with cardiovascular and pulmonary diseases. This category requires at least 250 hours of hands-on leadership experience, or an academic background in an appropriate allied health field. Examples of general objectives for an Exercise Leader in exercise physiology include to:

1. Define aerobic and anaerobic metabolism2. Describe the role of carbohydrates, fats, and proteins as fuel for aerobic and anaerobic

exercise performance3. Define the relationship of METs and kilocalories to levels of physical activity


Health/Fitness Instructor

An undergraduate degree in exercise science, kinesiology, physical education, or

appropriate allied health field represents the minimum education prerequisite for a Health/Fitness Instructor. These individuals must demonstrate competency in physical fitness testing, designing and executing an exercise program, leading exercise, and organizing and operating fitness facilities. The Health/Fitness Instructor has added responsibility for (a) training and/or supervising exercise leaders during an exercise program, and (b) serving as an exercise leader. Health/Fitness Instructors also function as health counselors to offer multiple intervention strategies for lifestyle change.Health/Fitness Director

The minimum educational prerequisite for Health/Fitness Director certification requires a postgraduate degree in an appropriate allied health field. Health/Fitness Directors must acquire a Health/Fitness Instructor or Exercise Specialist certification. This level requires supervision by a certified program director and physician during an approved internship, or at least 1 year of practical experience. Health/Fitness Directors require leadership qualities that ensure competency in training and supervising personnel, and proficiency in oral presentations.

ACSM Clinical TrackThe title “clinical” indicates that certified personnel in

these areas provide leadership in health and fitness and/or clinical programs. These professionals possess added clinical skills and knowledge that allow them to work with higher risk, symptomatic populations.Exercise Test Technologist

Exercise Test Technologists administer exercise tests to individuals in good health and various states of illness. They need to demonstrate appropriate knowledge of functional anatomy, exercise physiology, pathophysiology, electrocardiography, and psychology. They must know how to recognize contraindications to testing during preliminary

FOR YOUR INFORMATIONTHE AMERICAN COLLEGE OF SPORTS MEDICINEThe American College of Sports Medicine (ACSM) has more than 20,000 International, National, and Regional Chapter members. ACSMs Mission promotes and integrates scientific research, education, and practical applications of sports medicine and exercise science to maintain and enhance physical performance, fitness, health, and quality of life. The ACSM was founded in 1954. Since then, members have applied their knowledge, training and dedication in sports medicine and exercise science to promote healthier lifestyles for people around the globe. In 1984, the National Center relocated to its current headquarters in Indianapolis, Indiana. The ACSM continues to grow and prosper both nationally and internationally. Working in a wide range of medical specialties, allied health professions and scientific disciplines, ACSM is committed to the diagnosis, treatment, and prevention of sports-related injuries and the advancement of the science of exercise. The ACSM represents the largest, most respected sports medicine and exercise science organization in the world.


screening, administer tests, record data, implement emergency procedures, summarize test data, and communicate test results to other health professionals. Certification as an Exercise Test Technologist does not require prerequisite experience or special level of education.

Preventive/Rehabilitative Exercise SpecialistUnique competencies for the category Preventive/Rehabilitative Exercise Specialist include

the ability to lead exercises for persons with medical limitations (particularly cardiorespiratory and related diseases) and healthy populations. The position requires a bachelors or graduate degree in an appropriate allied health field and an internship of six months or more (800 hours), largely with cardiopulmonary disease patients in a rehabilitative setting. The preventive/rehabilitative exercise specialist conducts and administers exercise tests, evaluates and interprets clinical data and formulates an exercise prescription, conducts exercise sessions, and demonstrates leadership, enthusiasm, and creativity. This person can respond appropriately to complications during exercise testing and training, and can modify exercise prescriptions for patients with specific needs.

FOR YOUR INFORMATIONWhat’s in a Name?A lack of unanimity exists for the name of departments offering degrees (or even coursework) in exercise physiology. The list below presents 45 examples of different names of departments in the United States that offer essentially the same area of study. Each provides some undergraduate or graduate emphasis in exercise physiology (e.g., one or several courses, internships, work-study programs, laboratory rotations, or in-service programs.

Allied Health Leisure ScienceAllied Health Sciences Movement and Exercise ScienceExercise and Movement Science Movement StudiesExercise and Sport Science Nutrition and Exercise ScienceExercise and Sport Studies Nutritional and Health SciencesExercise Science Performance and Sport ScienceExercise Science and Human Movement Physical CultureExercise Science and Physical Therapy Physical EducationHealth and Human Performance Physical Education and Exercise ScienceHealth and Physical Education Physical Education and Human MovementHealth, Physical Education, Recreation & Dance Physical Education and Sport ProgramsHuman Biodynamics Physical Education and Sport ScienceHuman Kinetics Physical TherapyHuman Kinetics and Health RecreationHuman Movement Recreation and Wellness ProgramsHuman Movement Sciences Science of Human MovementHuman Movement Studies Sport and Exercise ScienceSport Management Human Movement Studies and PEHuman Performance Sport, Exercise, and Leisure ScienceHuman Performance and Health Promotion Sports ScienceHuman Performance and Leisure Studies Sport Science and Leisure StudiesHuman Performance and Sport Science Sport Science and Movement EducationInterdisciplinary Health Studies Sport StudiesIntegrative Biology Wellness and FitnessKinesiology Wellness EducationKinesiology and Exercise Science


Preventive/Rehabilitative Program DirectorThe Preventive/Rehabilitative Program Director holds an advanced degree in an appropriate

allied health-related area. The certification requires an internship or practical experience of at least 2 years. This health professional works with cardiopulmonary disease patients in a rehabilitative setting, conducts and administers exercise tests, evaluates and interprets clinical data, formulates exercise prescriptions, conducts exercise sessions, responds appropriately to complications during exercise testing and training, modifies exercise prescriptions for patients with specific limitations, and makes administrative decisions regarding all aspects of a specific program.Selected ReferencesACSM,s Guidelines for Exercise Testing and Prescription, sixth edition, Baltimore, Lippincott

Williams & Wilkins, 2000ASCM’s Guidelines to Exercise Testing and Prescription. 5th Ed. Baltimore, MD: Williams &

Wilkins, 1995.Blair, S., et al. (eds.) Resource Manual for Guidelines for Exercise Testing and Prescription.

Philadelphia: Lea & Febiger, 1988.

FOR YOUR INFORMATIONSEARCHING FOR EXERCISE SCIENCE INFORMATION: THE WEB OF SCIENCEProfessionals in the field continually need to research information about a specific topic or must locate research articles by specific scientists. The Web of Science <http://www.isinet.com/products/citation/wos/> provides a unique web based search tool, permitting extra-ordinary searching of many different databases. The Web of Science accesses multidisciplinary databases of bibliographic information gathered from thousands of scholarly journals. Each database is indexed so as to enable a search for a specific article by subject, author, journal, and/or author address. The information stored about each article includes the article's cited reference list (often called its bibliography), and searches can include the databases for articles that cite a known author or work. With the Web of Science you can: (1) search the databases for published works, (2) view full bibliographic records and add them to your Marked List for export to bibliographic management software, (3) save them to a file, (4) format them for printing, (5) e-mail them, (6) order the full text,(7) link directly to other articles on the same topic as the one you are viewing, even articles that have been published after the article you are viewing, and (8) save your search statements, which can be opened later and run again. Use the following URL for a tutorial on using the Web of Science: http://www.isinet.com/tutorials/webofscience/.

http://www.isinet.com/tutorials/webofscience/


Reading #3 Study Guide

Define Key Terms and Concepts17. Exercise physiologist

18. Clinical setting

19. Sports medicine and exercise physiology

20. Sports medicine professional

21. ACSM certification.

22. Health and fitness track

23. Exercise leader

24. Health/fitness instructor

25. Health/fitness director

26. ACSM

27. Clinical track

28. Exercise test technologist

29. Preventive/rehabilitative exercise specialist


30. Preventive/rehabilitative program director

31. The Web of Science

STUDY QUESTIONS

Introduction: The Exercise PhysiologistDo all states require accreditation to become an exercise physiologist?

What Do Exercise Physiologists Do?Name three different careers that an exercise physiologist can do.

1.

2.

The Exercise Physiologist/Health-Fitness Professional in the Clinical SettingName three different health-care professionals that typically work with an exercise physiologist.

1.

2.

3.

Sports Medicine and Exercise Physiology: A Vital LinkName two types of populations that sports medicine and exercise physiologists typically work with.

1.

2.

Name three different journals that publish exercise physiology research articles

1.

2.


3.

Training and Certification by Professional OrganizationsName four organizations that certify different types of health-care professionals.

1. 3.

2. 4.

ACSM Qualifications and CertificationsList four different competencies required for individuals interested in ACSM certifications.

1. 3.

2. 4.

Health and Fitness TrackName three categories of ACSMs health and fitness track.

1.2.3.

ACSM Clinical TrackName three categories of ACSMs health and fitness track.

1.

2.

3.

Figure 1. Bomb calorimeter directly measures the energy value of food.


LECTURE #4MEASUREMENT OF HUMAN ENERGY EXPENDITURE

IntroductionIn this lecture I introduce concepts related to the measurement of energy expenditure in

humans. These procedures form the basis for accurately quantifying differences among individuals in energy metabolism at rest and during physical activity.

The Energy Content of Food

The Calorie – A Measurement Unit of Food EnergyOne calorie expresses the quantity of heat to raise the temperature of 1 kg (1 L) of

water 1°C (specifically, from 14.5 to 15.5°C). For example, if a particular food contains 300 kCal, then releasing the potential energy trapped within this food's chemical structure increases the temperature of 300 L of water 1°C. Different foods contain different amounts of potential energy. One-half cup of peanut butter, for example, with a caloric value of 759 kCal contains the equivalent heat energy to increase the temperature of 759 L of water 1°C.

Gross Energy Value of FoodsLaboratories use a bomb calorimeter, similar to the one illustrated in Figure 1, to measure

the total (gross) energy value of a food macronutrient. Bomb calorimeters operate on the principle of direct calorimetry, measuring the heat liberated as the food burns completely.

The bomb calorimeter works as follows: A small, insulated chamber

filled with oxygen under pressure contains a weighed portion of food.

The food ignites and literally explodes and burns when an electric current ignites a fuse inside the chamber.

A surrounding water bath absorbs the heat released as the food burns (termed the heat of combustion). Insulation prevents loss of heat to the outside.

A sensitive thermometer measures the amount of heat absorbed by the water. For example, the combustion of one 4.7 oz, 4-inch sector of apple pie liberates 350 kCal of heat energy. This would raise 3.5 kg (7.7 lb) of ice water to the boiling point.

Heat of CombustionThe heat liberated by burning or oxidizing food in a bomb calorimeter represents its heat of

combustion or the total energy value of the food. Burning 1 g of pure carbohydrate yields a heat of combustion of 4.20 kCal, 1 g of pure protein releases 5.65 kCal, and 1 g of pure lipid yields 9.45 kCal. Because most foods in the diet consist of various proportions of the three


macronutrients, the caloric value of a given food reflects the sum of the heats of combustion of each of the macronutrients in the food.

The average heats of combustion for the three nutrients (carbohydrate = 4.2 kCal•g-1; lipid = 9.4 kCal kCal•g-1; protein = 5.65 kCal kCal•g-1) demonstrates that the complete oxidation of lipid in the bomb calorimeter liberates about 65% more energy per gram than protein oxidation, and 120% more energy than the oxidation of 1 g carbohydrate.

Net Energy Value of FoodsDifferences exist in the energy value of foods when comparing their heat of combustion

(gross energy value) determined by direct calorimetry to the net energy actually available to the body. This pertains particularly to proteins because the nitrogen component of this nutrient cannot be oxidized. In the body, nitrogen atoms combine with hydrogen to form urea, which excrets in urine. Elimination of hydrogen represents a loss of about 19% of the protein's potential energy. The hydrogen loss reduces protein's heat of combustion in the body to approximately 4.6 kCal per gram instead of 5.65 kCal per gram from oxidation in a bomb calorimeter. In contrast, identical fuel values determined by bomb calorimetry exist for

carbohydrates and lipids (which contain no nitrogen) compared to their heats of combustion in a bomb calorimeter.

DIGESTIVE EFFICIENCY

The “availability” to the body of the ingested macronutrients determines their ultimate caloric yield. Availability refers to completeness of digestion and absorption. Normally about 97% of carbohydrates, 95% of lipids, and 92% of proteins become digested, absorbed, and available to the body for energy. Large variation exists for protein ranging from a high of 97% for animal protein to a low 78% for dried peas and beans. Furthermore, less energy becomes available from a meal with high fiber content. Considering average digestive efficiencies, the net kCal value per gram for carbohydrate equals 4.0, 9.0 for lipid, and 4.0 for protein. These corrected heats of combustion comprise the “Atwater Factors,” named after the scientist who first studied the energy release from food in the calorimeter, and in the body.

Energy Value of a MealIf the composition and

weight of a food are known, the caloric content of any portion of food or an entire meal can be termed using the

FOR YOUR INFORMATIONMORE LIPID EQUALS MORE CALORIESLipid-rich foods contain a higher energy content than fat-free foods. One cup of whole milk, for example, contains 160 kCal, whereas the same quantity of skimmed milk (without fat) contains only 90 kCal. If a person who normally consumes one quart of whole milk each day switches to skimmed milk, the total calories ingested each year would be reduced by the equivalent calories in 25 lbs of body fat. In three years, all other things remaining constant, the loss of body fat would equal 75 lbs!

Table 1. Method of calculating the caloric value of a food from its composition of nutrients.

Composition

Atwater Factor(kCal•g-1)

PercentageTotal gramsIn one gramKCal• g-1

Protein

44%4.0

0.04 g0.16

(0.04 x 4.0=0.16)

Fat

913%13.0

0.13 g1.17

(0.13 x 9.0=1.17)

Carbohydrate

421%21.0

0.21 g0.84

(0.21 x 4.0=0.84)Total kCal per gram: 0.16 + 1.17 + 0.84 = 2.17 kCalTotal kCal per 100 grams: 2.17 x 100 = 217 kCal


Atwater factors. Table 1 illustrates the method for calculating the kCal value of 100 g (3.l5 oz) of vanilla ice cream. Based on laboratory analysis, vanilla ice cream contains about 4% protein, 13% lipid, and 21% carbohydrate, with the remaining 62% water. Thus, each gram of ice cream contains 0.04 g protein, 0.13 g lipid, and 0.21 g carbohydrate. Using these compositional values and the Atwater factors the kCal value per gram of ice cream is determined as follows: The net kCal value indicate that 0.04 g of protein contains 0.16 kCal (0.04 x 4.0 kCal•g-1), 0.13 g of lipid contains 1.17 kCal (0.13 x 9 kCal•g-1, and 0.21 g of carbohydrate contains 0.84 kCal (0.21 g x 4.0 kCal•g-1. Combining the separate values for the nutrients yields a total energy value for each gram of vanilla ice cream equal to 2.17 kCal (0.16 + 1.17 + 0.84). A 100-g serving yields a caloric value 100 times as large, or 217 kCal. Increasing or decreasing portion sizes or adding rich sauces or candies, or, conversely, adding fruits or calorie-free substitutes will affect the kCal content accordingly. Fortunately, the need seldom exists to compute the kCal value of foods because the United States Department of Agriculture (USDA) has already made these determinations for most foods.

Calories Equal CaloriesWhen examining the energy value of various foods, one makes a rather striking observation

with regard to a food’s energy value. Consider, for example, five common foods: raw celery, cooked cabbage, cooked asparagus spears, mayonnaise, and salad oil. To consume 100 kCal of each of these foods, one must eat 20 stalks of celery, 4 cups of cabbage, 30 asparagus spears, but only 1 tablespoon of mayonnaise or 4/5 tablespoon of salad oil. The point is that a small serving of some foods contains the equivalent energy value as a large quantity of other foods. Viewed from a different perspective, to meet daily energy needs a sedentary young adult would have to consume more than 4000 stalks of celery, 800 cups of cabbage, or 30 eggs, yet only 1.5 cups of mayonnaise or about 8 ounces of salad oil! The major difference among these foods is that high-fat foods contain more energy with little water. In contrast, foods low in fat or high in water tend to contain relatively little energy. An important concept, however, is that 100 kCal from mayonnaise and 100 kCal from celery are exactly the same in terms of energy.

Also note that a calorie reflects food energy regardless of the food source. Thus, from an energy standpoint, 100 calories from mayonnaise equals the same 100 calories in 20 celery stalks. The more one eats of any food, the more calories one consume. However, a small quantity of fatty foods represents a considerable quantity of calories; thus, the term “fattening” often misdescribes these foods. An individual's caloric intake equals the sum of all energy consumed from either small or large quantities of foods. Celery would become a “fattening” food if consumed in excess!

Heat Produced by the Body

CalorimetryThe principles of human heat production is summarized below:

FOR YOUR INFORMATIONEQUIVALENTS FOR 100 CALORIES• 20 stalks of celery • 2 bites (1/16) of a Big Mac• 4 cups cooked cabbage • 9 oz skim mile• 1-tablespoon mayonnaise • 5 oz whole milk

INDIRECT CALORIMETRY

DIRECT CALORIMETRY

MEASURE EITHER HEAT OR

O2

FOODSTUFF + OXYGEN –––––> HEAT + CO2 + H2O

Figure 2. Directly measuring the body’s heat production in a human calorimeter.


Calorimetry involves the measurement of heat dissipation, which is a direct measure of Calorie expenditure. One can measure heat directly (direct calorimetry) or the amount of oxygen consumed (indirect calorimetry) to indicate caloric expenditure by the body.

Direct CalorimetryAll of the body's

metabolic processes ultimately result in heat production. Consequently, we can measure human heat production similarly to the method used to determine the caloric value of foods in the bomb calorimeter (refer to Figure 1, above).

The human calorimeter illustrated in Figure 2 consists of an airtight chamber where a person lives and works for extended periods. A known volume of water at a specified temperature circulates through a series of coils at the top of the chamber. Circulating

CALORIMETRY

Direct Indirect

CO2 +N2 BalanceOxygen Consumption

Open Circuit Closed Circuit

METABOLISM

Figure 3. Closed-circuit method uses a spirometer prefilled with 100% oxygen. This method works well for rest or light exercise, but not for intense exercise.


water absorbs the heat produced and radiated by the individual. Insulation protects the entire chamber so any change in water temperature relates directly to the individual’s energy metabolism. For adequate ventilation, chemicals continually remove moisture and absorb carbon dioxide from the person’s exhaled air. Oxygen added to the air recirculates through the chamber.

Professors Atwater (a chemist) and Rosa (a physicist) in the 1890s built and perfected the first human calorimeter of major scientific importance at Wesleyan University (Connecticut). Their elegant human calorimetric experiments relating energy input to energy expenditure successfully verified the law of the conservation of energy and validated the relationship between direct and indirect calorimetry. The Atwater-Rosa Calorimeter consisted of a small chamber where a subject lived, ate, slept, and exercised on a bicycle ergometer or treadmill. Experiments lasted from several hours to 13 days; during some experiments, subjects performed cycling exercise continuously for up to 16 hours expending more than 10,000 kCal! The calorimeter's operation required 16 people working in teams of eight for 12-hour shifts.

Direct measurement of heat production in humans has considerable theoretical implications, but limited practical application. Accurate measurements of heat production in the calorimeter require considerable time, expense, and formidable engineering expertise. Thus, the calorimeters use remains generally inapplicable for human energy determinations for most sport, occupational, and recreational activities. Also, direct calorimetry cannot be applied for large-scale studies in underdeveloped and poor countries. Great need exists for total nutritional and energy balance assessments under a variety of deprivation conditions, particularly undernutrition and starvation. In the 90 years since Atwater and Rosa published their papers on human calorimetry, other methodology evolved to infer energy expenditure indirectly from metabolic gas exchanges (see next section). For example, the modern space suit worn by astronauts, in reality a “suit-calorimeter,” maintains respiratory gas exchange and thermal balance while the astronaut works outside an orbiting space vehicle.

Indirect CalorimetryAll energy-releasing reactions in the body ultimately depend on oxygen utilization.

By measuring a person’s oxygen uptake during steady-rate exercise, researchers obtain an indirect yet accurate estimate of energy expenditure. Indirect calorimetry remains relatively simple and less expensive to maintain and staff compared to direct calorimetry. Closed-circuit and open-circuit spirometry represent the two common methods of indirect calorimetry.

Closed-Circuit SpirometryFigure 3 illustrates the technique of closed-

circuit spirometry developed in the late 1800's and now used in hospitals and research laboratories to estimate resting energy expenditure. The subject breathes 100% oxygen from a prefilled container (spirometer). The equipment consists of a "closed system" because the person rebreathes only the gas in the spirometer. A canister of soda lime (potassium hydroxide) placed in the breathing circuit absorbs the carbon dioxide in the exhaled air. A drum attached to the spirometer revolves at a known speed and records oxygen uptake from changes in the system's volume.

Figure 4. Portable spirometer.

Figure 5. Bag technique to measure oxygen consumption.


During exercise, oxygen uptake measurement using closed-circuit spirometry becomes problematic. The subject must remain close to the equipment, the breathing circuit offers great resistance to the large gas volumes exchanged during exercise, and the relatively slow speed of carbon dioxide removal becomes inadequate during heavy exercise.

Open-Circuit SpirometryThe open-circuit method remains the most widely used technique to measure oxygen uptake

during exercise. A subject inhales ambient air with a constant composition of 20.93% oxygen, 0.03% carbon dioxide, and 79.04% nitrogen. The nitrogen fraction also includes a small quantity of inert gases. Changes in oxygen and carbon dioxide percentages in expired air compared to inspired ambient air indirectly reflect the ongoing process of energy metabolism. Thus, analysis of two factors volume of air breathed during a specified time period, and composition of exhaled air provide a useful way to measure oxygen uptake and infer energy expenditure.

Three common open-circuit, indirect calorimetric procedures measure oxygen uptake during physical activity:

Portable spirometry Bag technique Computerized instrumentation

Portable SpirometryGerman scientists in the early 1940’s perfected a lightweight,

portable system to determine indirectly the energy expended during physical activity. The activities included war-related operations traveling over different terrain with full battle gear, operating transportation vehicles, and tasks soldiers would encounter during combat operations. The person carries the 3-kg box-shaped apparatus (Figure 4) on the back. Air passes through a two-way valve, and expired air exits through a gas meter. The meter measures expired air volume and collect a small gas sample for later analysis of O2 and CO2 content, and thus determination of oxygen uptake and energy expenditure.

Carrying the portable spirometer allows considerable freedom of movement for estimating energy expenditure in diverse activities like mountain climbing, downhill skiing, sailing, golf, and common household activities. The equipment becomes

cumbersome during vigorous activity; with rapid breathing, the meter under-records airflow measurements during heavy exercise.Bag TechniqueFigure 5 depicts the bag technique. The subject rides a stationary cycle ergometer wearing headgear containing a two-way, high-velocity, low-resistance breathing valve. He breathes ambient air through one side of the valve and expels it out the other side. The air then passes into either large canvas or plastic bags or rubber meteorological balloons, or directly through a gas meter, which continually measures expired air volume. The meter collects a small sample of expired air for analysis of oxygen and carbon dioxide composition.


Assessment of oxygen uptake (as with all indirect calorimetric techniques) uses an appropriate calorific transformation to convert measures of oxygen uptake to energy expenditure. Figure 6 illustrates oxygen uptake measured by the bag technique while lifting boxes of different weight and size to evaluate the energy requirements of a specific occupational task.Computerized Instrumentation

With advances in computer and microprocessor technology, the exercise scientist can accurately and rapidly measure metabolic and cardiovascular response to exercise. A computer interfaces with different instruments to measure oxygen uptake.

The computer performs metabolic calculations based on electronic signals it receives from the instruments. A printed or graphic display of the data appears during the measurement period. More advanced systems include automated blood pressure, heart rate, and temperature monitors, and preset instructions to regulate speed, duration, and workload of a treadmill, bicycle ergometer, stepper, rower, swim flume, or other exercise apparatus.

Caloric Transformation for OxygenBomb calorimeter studies show that approximately 4.82 kCal release when a blend of

carbohydrate, lipid, and protein burns in one liter of oxygen. Even with large variations in metabolic mixture, this calorific value for oxygen varies only slightly (generally within 2 to 4%). Assuming the combustion of a mixed diet, a rounded value of 5.0 kCal per liter of oxygen consumed designates the appropriate conversion factor for estimating energy expenditure under steady-rate conditions of aerobic metabolism. An energy-oxygen equivalent of 5.0 kCal per liter provides a convenient yardstick for transposing any aerobic physiologic activity to a caloric (energy) frame of reference. In fact, indirect calorimetry through

oxygen uptake measurement serves as the basis to quantify the caloric stress of most physical activities.

The Respiratory Quotient (RQ)Complete oxidation of a molecule's carbon and hydrogen atoms to the carbon dioxide and

water end-products requires different amounts of oxygen due to inherent chemical differences in carbohydrate, lipid, and protein composition. Thus, the substrate metabolized determines the quantity of carbon dioxide produced in relation to oxygen consumed. The respiratory quotient (RQ) refers to the following ratio of metabolic gas exchange:

RQ = CO2 produced O2 uptakeThe RQ provides a convenient guide for approximating the nutrient mixture catabolized for

energy during rest and aerobic exercise. Also, because the caloric equivalent for oxygen differs somewhat depending on the nutrients oxidized, precisely determining the body's heat production requires knowledge of both RQ and oxygen uptake.

RQ For Carbohydrate, Lipid and ProteinBecause the ratio of hydrogen to oxygen atoms in carbohydrates is always the same as in

water, that is 2:1, the complete oxidation of a glucose molecule consumes six molecules of oxygen and six carbon dioxide molecules as follows:

C6H12O6 + 6 O2 6 CO2 + 6 H2OGas exchange during glucose oxidation produces an equal number of CO2

molecules to O2 molecules consumed; therefore, the RQ for carbohydrate equals 1.00:

RQ = 6CO2 6O2 =1.00


The chemical composition of lipids differs from carbohydrates because lipids contain considerably fewer oxygen atoms in proportion to carbon and hydrogen atoms. Consequently, when a lipid catabolizes for energy, additional oxygen is required for the oxidation of the hydrogen atoms in excess of their 2 to 1 ratio with oxygen. Palmitic acid, a typical fatty acid, oxidizes to carbon dioxide and water, producing 16 carbon dioxide molecules for every 23 oxygen molecules consumed. The following equation summarizes this exchange to compute RQ:

C16H32O2 + 23O2 16CO2 + 16H2ORQ = 16CO2 23O2 = 0.696

Generally, a value of 0.70 represents the RQ for lipid with variation ranging between 0.69 and 0.73, depending on the oxidized fatty acid's carbon chain length.Proteins do not simply oxidize to carbon dioxide and water during energy metabolism in the

body. Rather, the liver first deaminates the amino acid molecule; then the body excretes the nitrogen and sulfur fragments in the urine, sweat, and feces. The remaining “keto acid” fragment oxidizes to carbon dioxide and water to provide energy for biologic work. Short-chain keto acids, as in fat catabolism, require more oxygen in relation to carbon dioxide produced to achieve complete combustion. The protein albumin oxidizes as follows:

C72H112N2O22S + 77O2 63CO2 + 38H2O + SO3 + 9CO(NH2)2

RQ = 63CO2 77O2 = 0.818The general value 0.82 characterizes the RQ for protein.

RQ For a Mixed DietDuring activities ranging from complete bed rest to mild aerobic exercise (walking or slow

jogging), the RQ seldom reflects the oxidation of pure carbohydrate or pure fat. Instead, metabolism of a mixture of these nutrients occurs with an RQ intermediate between 0.70 and 1.00. Assume an RQ of 0.82 from the metabolism of a mixture of 40% carbohydrate and 60% fat, applying the caloric equivalent of 4.825 kCal per liter of oxygen for the energy transformation. Using 4.825 kCal, the maximum error in estimating energy metabolism from steady-rate VO2 would equal about 4%.

Thermal Equivalents of Oxygen: The RQ TableTable 2 (next page) presents the energy expenditure per liter VO2 for different non-protein

RQ values, including corresponding percentages and grams of carbohydrate and fat used for energy. The non-protein value assumes that the metabolic mixture comprises only carbohydrate and fat. Interpret the table as follows:

Suppose oxygen uptake during 30 min of exercise averages 3.22 L•min–1 with CO2 production of 2.78 L . min-1. The RQ, computed as VCO2/VO2 (2.78/3.22), equals 0.86. From Table 1, this RQ value (left column) corresponds to an energy equivalent of 4.875 kCal per liter of oxygen uptake, or an energy output of 15.7 kCal•min–1 (2.78 L O2•min–1 x 4.875 kCal). Based on a non-protein RQ, 54.1% of the calories come from the combustion of carbohydrate and 45.9% from fat. The total calories expended during the 30-minute exercise period equal 471 kCal (15.7 kCal•min–1 x 30).

FOR YOUR INFORMATION

Liters of Oxygen and Calories


• 1 Liter per minute Oxygen Consumed = 5 kCal per minute heat liberated

• Rest oxygen consumption during rest = 250 mL (0.25 L) per minute

• 5 kCal per Liter x 0.25 Liters = 1.25 kCal per minute (5 x 0.25 = 1.25)

• kCal per hour = 60 minutes x 1.25 kCal per minute = 75 kCal per hour

• kCal per 24 hour = 24 h x 75 kCal per h = 1800 kCal per 24 h


Table 2. Thermal equivalents of oxygen for the non-protein respiratory quotient, including percent kCal and grams derived from carbohydrate and fat.

Non-Protein

RQ

kCal per Liter O2 Uptake

% kCal Derived from

CHO

%kCal Derived

From Fat

Grams per Liter O2

CHO

Grams per Liter O2

Fat0.7 4.686 0.0 100.0 0.000 0.496

0.71 4.69 0.1 98.9 0.120 0.4910.72 4.702 4.8 95.2 0.510 0.4760.73 4.714 8.4 91.6 0.900 0.4600.74 4.727 12.0 88.0 0.130 0.4440.75 4.739 15.6 84.4 0.170 0.4280.76 4.75 19.2 80.8 0.211 0.4120.77 4.764 22.8 77.2 0.250 0.3960.78 4.776 26.3 73.7 0.290 0.3800.79 4.788 29.9 70.1 0.330 0.3630.8 4.801 33.4 66.6 0.371 0.347

0.81 4.813 36.9 63.1 0.413 0.3300.82 4.825 40.3 59.7 0.454 0.3130.83 4.838 43.8 56.2 0.496 0.2970.84 4.85 47.2 52.8 0.537 0.2800.85 4.862 50.7 49.3 0.579 0.2630.86 4.875 54.1 45.9 0.621 0.2470.87 4.887 57.5 42.5 0.663 0.2300.88 4.889 60.8 39.2 0.705 0.2130.89 4.911 64.2 35.8 0.749 0.1950.9 4.924 67.5 32.5 0.791 0.178

0.91 4.936 70.8 29.2 0.834 0.1600.92 4.948 74.1 25.9 0.877 0.1430.93 4.961 77.4 22.6 0.921 0.1250.94 4.973 80.7 19.3 0.964 0.1080.95 4.985 84.0 16.0 1.008 0.0900.96 4.998 87.2 12.8 1.052 0.0720.97 5.01 90.4 9.6 1.097 0.0540.98 5.022 93.6 6.4 1.142 0.0360.99 5.035 96.8 3.2 1.186 0.018

1 5.047 100.0 0.0 1.231 0.000


RREADING #4 STUDY GUIDE


1. 4.2 kcal•gm-1

2. 5.65 kcal•gm-1

3. 9.4 kcal•gm-1

4. Atwater factors

5. Bomb calorimeter

6. Calorie

7. Direct calorimetry

8. Closed-circuit spirometry

9. Digestive efficiency

10.Direct calorimetry

11.Heat of combustion

12.Indirect calorimetry


13.Open-circuit spirometry

14.Respiratory exchange ratio

STUDY QUESTIONS

The Calorie – A Measurement Unit of Food EnergyDescribe the difference between a calorie and a kilocalorie.

Gross Energy Value of FoodsDescribe the instrument in direct calorimetry to measure a food’s energy content?

Heat of CombustionGive the heats of combustion for the three macronutrients>

Carbohydrate

Lipid

Protein

Why is the heat of combustion for protein less in the body than in a bomb calorimeter?

Net Energy Value of FoodsCompare the heat of combustion of carbohydrates and lipids in the body and determined by bomb calorimetry.

In the body

Bomb calorimetry

Digestive EfficiencyList one effect that dietary fiber has on the energy availability of ingested foods?


Energy Value of a MealCalculate the caloric content of 100 grams of a food containing 5% protein, 14% lipid, and 20% carbohydrate. (Hint: Use the Atwater general factors.)

Calories Equal CaloriesFrom an energy standpoint, explain why 100 calories from a piece of cake is no more fattening that 100 kcal from celery?

Heat Produced by the BodyList two methods to determine heat production by the body.

1.

2.

CalorimetryBriefly describe the principle of calorimetry.

Direct CalorimetryDescribe direct calorimetry to measure human heat production.

Indirect CalorimetryList the two methods of indirect calorimetry.

1.

2.

Closed-Circuit SpirometryGive one disadvantage of closed-circuit spirometry during exercise studies

Open-Circuit Spirometry


List one positive aspect of each of the following procedures of indirect calorimetry during exercise studies.

Portable Spirometry

Bag Technique

Computerized Instrumentation

Portable SpirometryWho were the first scientists to use portable spirometry?

Bag TechniqueWhat kind of breathing valve must be used with the bag technique for open-circuit spirometry?

Computerized InstrumentationLists three instruments that need to be interfaced with a computer for on-line measurement of oxygen uptake.

1. 3.

2.

Direct Versus Indirect CalorimetryGive an example of the degree of agreement between energy expenditure obtained by direct and indirect calorimetry.

Caloric Transformation for OxygenAssuming combustion of a mixed diet, give the rounded value for the number of calories released per liter of oxygen consumed?

The Respiratory Quotient (RQ)Write the RQ formula.

RQ For Carbohydrate, lipid and proteinWrite the RQ for carbohydrate?


Write the RQ for lipid?

Write the RQ for protein?

RQ for A Mixed DietGive the RQ for a diet of approximately 40% carbohydrate and 60% lipid. What is the corresponding caloric equivalent?

RQ

Caloric equivalent


READING #5HUMAN ENERGY TRANSFER BASICS

IntroductionIn this lecture, I present an overview of how the body obtains energy to power its diverse

functions. A basic understanding of carbohydrate, fat, and protein catabolism and subsequent anaerobic and aerobic energy transfer forms the basis for much of the content of exercise physiology. Knowledge about human bioenergetics provides the practical basis for formulating sport-specific exercise training regimens, recommending activities for physical fitness and weight control, and advocating prudent dietary modifications for specific sport requirements.

The body’s capacity to extract energy from food nutrients and transfer it to the contractile elements in skeletal muscle determines the capacity to swim, run, bicycle, and ski long distances at high intensity. Energy transfer occurs through thousands of complex chemical reactions that require the proper mixture of macro- and micronutrients continually fueled by oxygen. The term aerobic describes such oxygen-requiring energy reactions. In contrast, anaerobic chemical reactions generate energy rapidly for short durations without oxygen. Rapid energy transfer allows for a high standard of performance in maximal short-term sprinting in track and swimming, or repeated stop-and-go sports like soccer, basketball, lacrosse, water polo, volleyball, field hockey, and football. The following point requires emphasis: The anaerobic and aerobic breakdown of ingested food nutrients provides the energy source for synthesizing the chemical fuel that powers all forms of biologic work.

Figure 1. ATP and it’s high energy bonds.


Part 1. ATP and Phosphate Bond EnergyThe human body receives a continual supply of chemical energy to perform its many

functions. Energy derived from the oxidation of food does not release suddenly at some kindling temperature because the body, unlike a mechanical engine, cannot use heat energy directly. Rather, complex, enzymatically-controlled reactions within in the relatively cool, watery medium of the cell extract the chemical energy trapped within the bonds of carbohydrate, fat, and protein molecules. This relatively slow extraction process reduces energy loss and provides for enhanced efficiency in energy transformations. In this way, the body makes direct use of chemical energy for biologic work. In a sense, energy becomes available to the cells as needed. The body maintains a continuous energy supply through the use of adenosine triphosphate, or ATP, the special carrier for free energy.

ATP – The Energy CurrencyThe energy in food does not transfer directly to cells for biologic work. Rather, this

“macronutrient energy” becomes released and funneled through the energy-rich compound ATP to power cellular needs. Figure 1 shows how an ATP molecule forms from a molecule of adenine and ribose (called adenosine), linked to three phosphate molecules. The bonds linking the two outermost phosphates, termed high-energy bonds, represent a considerable stored energy within the ATP molecule.

A tight linkage or coupling exists between the breakdown of the macronutrient energy molecules and ATP synthesis, which “captures” a significant portion of the released energy within its bonds. Coupled reactions occur in pairs; the breakdown of one compound provides energy for building another compound. To meet energy needs, ATP joins with water (in a process termed hydrolysis) splitting the outermost phosphate bond from the ATP molecule. The enzyme adenosine

triphosphatase accelerates this process forming a new compound adenosine

diphosphate or ADP. These reactions, in turn, couple to other reactions that use the “freed” phosphate-bond chemical energy. The body uses ATP to transfer the energy produced during catabolic reactions to power reactions that synthesize new materials. In essence, this energy receiver – energy donor cycle represents the cells' two major energy-transforming activities:

Form and conserve ATP from food's potential energy Use energy extracted from ATP to power biologic work

Figure 2 illustrates examples of the anabolic and catabolic reactions that involve the coupled transfer of chemical energy. All of the energy released from catabolizing one compound does not dissipate as heat; rather, a portion becomes harvested and conserved within the chemical structure of the newly formed compound. ATP represents the common energy transfer “vehicle” in most coupled biologic reactions.

Anabolism requires energy for synthesizing new compounds. For example, several glucose molecules join together, much like the links in a chain of sausages to form the larger more complex glycogen molecule; similarly, glycerol and fatty acids combine to make triglycerides, and amino acids link forming proteins. Each reaction starts with simple compounds and uses them as building blocks to form larger, more complex compounds. Catabolic reactions release energy; in many instances, this process couples to ATP formation.

During ATP catabolism, the enzyme adenosine triphosphatase catalyzes the reaction when ATP joins with water. For each mole of ATP degraded to adenosine diphosphate (ADP), the

Figure 2. Examples of anabolic and catabolic reactions that involve coupled energy transfer.


outermost phosphate bond splits, liberating approximately 7.3 kCal of free energy (i.e., energy available for work).

ATP + H2O ––––>ATP + P -7.3 kCalThe free energy liberated in ATP hydrolysis

reflects energy differences between reactants and end-products. Because this reaction generates considerable energy, ATP is referred to as a high-energy phosphate compound. Additional energy releases when another phosphate splits from ADP. In some reactions of biosynthesis, ATP donates its two terminal phosphates simultaneously to construct new cellular material. Adenosine monophosphate or AMP becomes the new molecule with a single phosphate group.

The energy liberated during ATP breakdown directly transfers to other energy-requiring molecules. In muscle, this energy activates specific sites on the contractile elements causing muscle fibers to shorten. Because energy from ATP powers all forms of biologic work, ATP constitutes the cell’s “energy currency.”

The splitting of an ATP molecule immediately takes place without oxygen. The cell’s capability for ATP breakdown generates energy for rapid use; this would not occur, however, if energy metabolism required oxygen at all times. Think of anaerobic energy release as a back-up power source, called upon to deliver energy in excess of what can be generated aerobically. For this reason, any form of activity can take place immediately without instantaneously consuming oxygen; examples include sprinting for a bus, lifting a fork, driving a golf ball, spiking a volleyball,

doing a pushup, or jumping up in the air. The well known practice of holding one’s breathe while sprint swimming provides a clear example

of ATP splitting without reliance on atmospheric oxygen. Withholding air (oxygen), although not advisable, can be done during a 100-yard sprint on the track, lifting a barbell, a dash up several flights of stairs, or simply holding one's breath while rapidly flexing and extending the arms or fingers. In each case, energy metabolism proceeds uninterrupted because the energy for performing the activity comes almost exclusively from intramuscular anaerobic sources.

ATP ResynthesisBecause cells store only a small quantity of ATP, it must continually be resynthesized at its

rate of use. This provides a biologically useful mechanism for regulating energy metabolism. By maintaining only a small amount of ATP, its relative concentration (and corresponding concentration of ADP) changes rapidly with any increase in a cell’s energy demands. An ATP:ADP imbalance at the start of exercise immediately stimulates the breakdown of other stored energy-containing compounds to resynthesize ATP. As one might expect, increases in cellular energy transfer depend on exercise intensity. Energy transfer increases about four-

Figure 3. ATP and PCr are anaerobic sources of phosphate-bond energy. The energy liberated from the hydrolysis (splitting) of PCr powers the union of ADP to reform ATP.


fold in the transition from sitting in a chair to walking. However, changing from a walk to an all-out sprint almost immediately accelerates energy transfer rate about 120 times! Generating significant energy output almost instantaneously demands ATP availability and a means for its rapid resynthesis.

ATP: A Limited CurrencyAs previously pointed out, a limited quantity of ATP serves as the energy currency for all

cells. In fact, at any one time the body stores only about 80 to 100 g (3.5 oz.) of ATP. This provides enough intramuscular stored energy for several seconds of explosive, all-out exercise. A limited quantity of “stored” ATP represents an advantage due to the molecule's heaviness. Biochemists estimate that sedentary persons each day use an amount of ATP approximately equal to 75% of their body mass. For an endurance athlete running a marathon race and generating about 20 times the resting energy expenditure over 3 hours, total ATP usage could amount to 80 kg! Thus, with limited supplies and with high demand, ATP must be continually resynthesized to meet energy requirements.

Phosphocreatine (PCr): The Energy Reservoir

Some energy for ATP resynthesis comes directly from the splitting (hydrolysis) of a phosphate from another intracellular high-energy phosphate compound – phosphocreatine (PCr), also known as creatine phosphate or CP. PCr, similar to ATP, releases a large amount of energy when the bond splits between the creatine and phosphate molecules. The hydrolysis of PCr for energy begins at the onset of intense exercise, does not require oxygen, and reaches a maximum in

about 10 seconds. Thus, PCr can be considered a “reservoir” of high-energy phosphate bonds. Figure 4 schematically illustrates the release

and use of phosphate-bond energy in ATP and PCr. The term high-energy phosphates describe these stored intramuscular compounds. ATP and PCr are anaerobic sources of phosphate-bond energy. The energy liberated from the hydrolysis (splitting) of PCr powers the union of ADP and P to reform ATP.

In both reactions in Figure 3, the arrows point in opposite directions to indicate reversible reactions. In other words, creatine (C) and phosphate (P) can join again to reform PCr. This also holds true for ATP where the union of ADP and P reforms ATP (see top part of figure). ATP resynthesis occurs if sufficient energy exists to rejoin an ADP molecule with one P molecule. Hydrolysis of PCr supplies this energy.

Cells store PCr in considerably larger quantities than ATP. Mobilization of CP for energy takes place almost instantaneously and does not require oxygen. For this reason, PCr is considered a “reservoir” of high-energy phosphate bonds.

Figure 4. In the body, the electron transport chain removes electrons from hydrogen and ultimately delivers them to oxygen. In this oxidation-reduction process, much of the chemical energy stored within the hydrogen atoms does not dissipate to kinetic energy, rather, it becomes conserved in forming ATP.


Cellular OxidationA molecule becomes reduced when it accepts electrons from an electron donor. In turn, the

molecule that gives up the electron becomes oxidized. Oxidation reactions (donating electrons) and reduction reactions (accepting electrons) remain coupled because every oxidation coincides with a reduction. In essence, cellular oxidation-reduction constitutes the mechanism for energy metabolism. The stored carbohydrate, fat, and protein molecules continually provide hydrogen atoms in this process. The mitochondria, the cell’s “energy factories,”

contain carrier molecules that remove electrons from hydrogen (oxidation) and eventually pass them to oxygen (reduction). Synthesis of the

high-energy phosphate ATP occurs during oxidation-reduction reactions.

Electron TransportFigure 4 illustrates the general scheme for hydrogen oxidation and accompanying electron

transport to oxygen. During cellular oxidation, hydrogen atoms are not merely turned loose in the cell fluid. Rather, highly specific enzymes catalyze hydrogen's release from the nutrient substrate. The coenzyme nicotinamide adenine dinucleotide or NAD+ accepts pairs of electrons (energy) from hydrogen. While the substrate oxidizes and loses hydrogen (electrons), NAD+ gains a hydrogen and two electrons and reduces to NADH; the other hydrogen appears as H+ in the cell fluid.

The riboflavin-containing coenzyme, flavin adenine dinucleotide (FAD) serves as the other important electron acceptor in oxidizing food fragments.

The NADH and FADH2 formed in macronutrient breakdown represent energy-rich molecules because they carry electrons with a high-energy transfer potential. The cytochromes, a series of iron-protein electron carriers, then pass in “bucket brigade” fashion pairs of electrons carried by NADH and FADH2 on the inner membranes of the mitochondria. The cytochromes transfer electrons to their ultimate destination, where they reduce oxygen to form water. The NAD+ and FAD then recycle for subsequent use in energy metabolism.

Electron transport by specific carrier molecules constitutes the respiratory chain, serving as the final common pathway where electrons extracted from hydrogen pass to oxygen. For each pair of hydrogen atoms, two electrons flow down the chain and reduce one atom of oxygen to form water. Of the five specific cytochromes, only the last one, cytochrome oxidase (cytochrome a3 with a strong affinity for oxygen), discharges its electron directly to oxygen.

In the body, the electron-transport chain removes electrons from hydrogen and ultimately delivers them to oxygen. In this oxidation-reduction process, much of the chemical energy stored within the hydrogen atom does not dissipate to kinetic energy; rather it becomes conserved in forming ATP.


Oxidative PhosphorylationOxidative phosphorylation refers to how ATP becomes synthesized during the

transfer of electrons from NADH and FADH2 to molecular oxygen. This important process represents the cell’s primary means for extracting and trapping chemical energy in the high-energy phosphates. Over 90% of ATP synthesis takes place in the respiratory chain by oxidative reactions coupled with phosphorylation.

Think of oxidative phosphorylation as a waterfall divided into several separate cascades by the intervention of waterwheels at different heights. The energy in NADH transfers to ADP to reform ATP at three distinct coupling sites during electron transport (Figure 4). Oxidation of hydrogen and subsequent phosphorylation occurs as follows:

NADH + H+ + 3ADP + 3 P + 1/2 O2 –––> NAD+ + H2O + 3 ATP

Role of Oxygen in Energy MetabolismThe continual resynthesis of ATP during coupled oxidative phosphorylation of the

macronutrients requires three prerequisites conditions.1. Availability of the reducing agents NADH2 or FADH2

2. Presence of an oxidizing agent in the form of oxygen3. Sufficient quantity of enzymes and metabolic machinery in the tissues to make the

energy transfer reactions “go” at the appropriate rateSatisfying these three conditions causes hydrogen and electrons to continually shuttle down

the respiratory chain to molecular oxygen during catabolism of food substrates. In strenuous exercise, inadequacy in oxygen delivery (condition #2) or its rate of utilization (condition #3) creates a relative imbalance between hydrogen release and oxygen's final acceptance of them. If either of these occurs, electron flow down the respiratory chain “backs up” and hydrogen accumulate bound to NAD+ and FAD.

For aerobic metabolism, oxygen serves as the final electron acceptor in the respiratory chain and combines with hydrogen to form water during energy metabolism. Some might argue that the term aerobic metabolism is misleading, since oxygen does not participate directly in ATP synthesis. Oxygen's presence at the “end of the line,” however, largely determines one’s capability for ATP production and, hence, the ability to sustain high-intensity exercise. In this sense, use of the term aerobic seems justified.

Part 2. Energy Release From Food


The energy released in macronutrient breakdown serves one crucial purpose – to phosphorylate ADP to reform the energy-rich compound ATP (Figure 5). Although macronutrient catabolism favors generating phosphate-bond energy, the specific pathways of degradation differ depending on the nutrients metabolized.

Energy Release from CarbohydrateCarbohydrate's primary function supplies energy for cellular work. Carbohydrate

represents the only macronutrient whose potential energy can generate ATP anaerobically. This becomes important in vigorous exercise that requires rapid energy release above levels supplied by aerobic metabolic reactions.

1. During light and moderate aerobic exercise, carbohydrate supplies about one-half of the body’s energy requirements.

2. Processing fat through the metabolic mill for energy requires some carbohydrate catabolism.

3. Aerobic breakdown of carbohydrate for energy occurs at about twice the rate as energy generated from fatty acid breakdown. Thus, depleting glycogen reserves significantly reduces exercise power output. In prolonged high-intensity, aerobic exercise such as marathon running, athletes often experience nutrient-related fatigue – a state associated with muscle and liver glycogen depletion.

The complete breakdown of 1 mole of glucose (180 g) to carbon dioxide and water yields 686 kcal of chemical free energy.

C6H12O6 + 6O2 ––––> 6CO2 + 6H2O + 689 kCal per moleIn the body, the complete breakdown of glucose liberates the same quantity of energy, with

a significant portion conserved as ATP. Synthesizing one mole of ATP from ADP and phosphate ion requires 7.3 kcal of energy. Therefore, coupling all of the energy from glucose oxidation to phosphorylation could theoretically form 94 moles of ATP per mole of glucose (686 kcal ÷ 7.3 kcal per mole = 94 moles). In the muscles, however, the phosphate bonds only conserve 38% or 263 kcal of energy, with the remainder dissipated as heat. This loss of useful energy

Figure 5. Potential energy in food powers ATP resynthesis

Figure 6. Glycolysis. A 6-carbon glucose splits into two, 3-carbon compounds that degrade into two, 3-carbon pyruvate molecules. Glucose splitting occurs anaerobically.


represents the body's metabolic inefficiency for converting stored potential energy into useful energy.

Anaerobic versus AerobicGlucose degradation occurs in two stages. In stage one, glucose breaks down to two

molecules of pyruvate. Energy transfers occur without oxygen (anaerobic). In stage two, pyruvate degrades further to CO2 and H2O. Energy transfers from these reactions require

electron transport and oxidative phosphorylation.

Anaerobic Energy from Glucose: Glycolysis (Glucose Splitting)

The first stage of glucose degradation within cells involves a series of ten chemical reactions collectively termed glycolysis (also termed the Embden-Meyerhof pathway for its discoverers); glycogenolysis describes these reactions when they begin with stored glycogen. These series of reactions occur in the watery medium of the cell outside of the mitochondrion. In a way, glycolytic reactions represent a more primitive form of energy transfer, well developed in amphibians, reptiles, fish, and marine mammals. In humans, the cells’ limited capacity for glycolysis becomes crucial during activities that require effort for up to 90-sec.

Figure 6 shows the glucose-to-pyruvate sequence under anaerobic conditions in terms of the carbon atoms. The six-carbon glucose splits into two 3-carbon compounds (pyruvate). These subsequently degrade into two molecules of pyruvate with the net release of 2 ATP (i.e., energy).

Formation of Lactic AcidSufficient oxygen bathes the cells during light-to-moderate of energy metabolism. The

hydrogen (electrons) stripped from the substrate and carried by NADH oxidizes within the mitochondria to form water as they join with oxygen.

In strenuous exercise, when energy demands exceed either oxygen supply or utilization, the respiratory chain cannot process all of the hydrogen joined to NADH. Continued release of anaerobic energy in glycolysis depends on NAD+ availability; otherwise, the rapid rate of glycolysis stops. In anaerobic glycolysis, NAD+ “frees-up” as pairs of “excess” non-oxidized hydrogen combine temporarily with pyruvate to form lactic acid, catalyzed by the enzyme lactic dehydrogenase (LDH) in the reversible reaction shown in Figure 7.

The temporary storage of hydrogen with pyruvate represents a unique aspect of energy metabolism because it provides a ready “storage bin” to temporarily hold the end products of anaerobic glycolysis. Also, once lactic acid forms within muscle, it diffuses rapidly into the blood for buffering to sodium lactate and removal from the site of energy metabolism. This

Figure 7. Lactate forms when excess hydrogen combines with pyruvate.

Figure 8. Two phases of the Citric Acid cycle. Phase 1 in the mitochondrion, Krebs cycle activity generates hydrogen atoms. Phase 2 – significant ATP regenerates when hydrogen oxidizes via the aerobic process of electron transport.


allows glycolysis to continue supplying additional anaerobic energy for ATP resynthesis. However, this avenue for extra energy remains temporary; blood lactate and muscle lactic acid levels increase and ATP regeneration cannot keep pace with its utilization rate. Fatigue soon sets in and exercise performance diminishes.

Even at rest, energy metabolism in red blood cells forms some lactic acid. This occurs as the red blood cells contain no mitochondria and must derive their energy from glycolysis. Lactic acid should not be viewed as a metabolic “waste product” as it provides a valuable source of energy that accumulates in the body during heavy exercise. When sufficient oxygen becomes available during recovery, or when exercise pace slows, NAD+ scavenges hydrogen attached to lactate; this hydrogen subsequently oxidizes to form ATP. Thus, blood lactate becomes an energy source as it readily reconverts to pyruvate to undergo further catabolism.

Aerobic Energy From Glucose: The Krebs CycleThe anaerobic reactions of glycolysis release about 10% of the energy within the original

glucose; thus, extracting the remaining energy requires additional metabolism. This occurs when pyruvate irreversibly converts to acetyl–CoA. Acetyl–CoA enters the second stage of carbohydrate breakdown known as the Krebs cycle (citric acid cycle). For each molecule of acetyl-CoA entering the Krebs cycle, two CO2 molecules and 4 pairs of hydrogen atoms release. One molecule of ATP also regenerates directly from the Krebs cycle.

Oxygen does not participate directly in the Krebs cycle. The aerobic process of electron transport-oxidative phosphorylation transfers the major portion of chemical energy in pyruvate to ADP. With adequate oxygen, enzymes and substrate, NAD and FAD regeneration takes place allowing Krebs cycle metabolism to proceed.


Figure 8 shows the two phases of Krebs cycle activity. Phase 1 involves the introduction of pyruvate (from glycolysis), combined with coenzyme A (a Vitamin B derivative), into the Krebs cycle with the release of hydrogen, CO2 and ATP. Phase 2 shows significant ATP regeneration when hydrogen oxidizes via the aerobic process of electron transport-oxidative phosphorylation (electron transport chain).

Net Energy Transfer From Glucose CatabolismFigure 9 gives the pathways for energy transfer during glucose breakdown in muscle. Two

ATP form from in glycolysis; and 2 ATP come from acetyl-CoA degradation in Krebs cycle. The 24 released H2 atoms (and their subsequent oxidation) are counted as follows:

Four extramitochondrial hydrogen (2 NADH) from glycolysis yield 4 ATP (6 ATP in heart, kidney, and liver).

Four hydrogen (2 NADH) released as pyruvate degrades to acetyl-CoA yield 6 ATP. Twelve of the 16 hydrogens (6 NADH) released in the Krebs cycle yield 18 ATP. Four hydrogen joined to FAD (2 FADH2) in the Krebs cycle yield 4 ATP.

Figure 9. Net yield of 36 ATP from energy transfer during the complete oxidation of one glucose molecule through glycolysis, the


Energy Release From FatStored fat represents the body’s most plentiful source of potential energy. Relative to

carbohydrate and protein, stored fat provides almost unlimited energy. The actual fuel reserves in an average young adult male represent between 60,000 and 100,000 kcal of energy from triglyceride in fat cells (adipocytes), and about 3000 kcal from intramuscular triglyceride stored in close proximity to the mitochondria. In contrast, the carbohydrate energy reserve would only contribute about 2000 kcal. Prior to energy release from fat, lipolysis splits the triglyceride molecule into glycerol and three water-insoluble fatty acid molecules. The enzyme lipase catalyzes triglyceride breakdown as follows:

Triglyceride + 3H2O ––––––> Glycerol + 3 Fatty acids

Breakdown of Glycerol and Fatty AcidsFigure 10 summarizes the pathways for the breakdown of the triglyceride molecule's

glycerol and fatty acid components.

Figure 11

Figure 10. Breakdown of glycerol and fatty acid fragments of a triglyceride molecule.


GlycerolThe anaerobic reactions of glycolysis accept glycerol as 3-phosphoglyceraldehyde, which

then degrades to pyruvate to form ATP by substrate-level phosphorylation. Hydrogen atoms pass to NAD+, and the Krebs cycle oxidizes pyruvate. The complete breakdown of the single glycerol molecule in a triglyceride synthesizes a total of 19 ATP molecules. Glycerol also provides carbon skeletons for glucose synthesis. The gluconeogenic role of glycerol becomes prominent when glycogen reserves deplete due to dietary restriction of carbohydrates, or in long-term exercise or heavy training.

Fatty AcidsThe fatty acid molecule transforms to acetyl-CoA in the mitochondrion during beta–

oxidation reactions. This involves the successive release of 2-carbon acetyl fragments split from the fatty acid's long chain. ATP phosphorylates the reactions, water is added, and hydrogen pass to NAD+ and FAD, and acetyl–CoA forms when the acetyl fragment joins with coenzyme A. This acetyl unit is the same one generated from glucose breakdown. Beta-oxidation continues until the entire fatty acid molecule degrades to acetyl–CoA so it can directly enter the Krebs cycle. Hydrogen released during fatty acid catabolism oxidizes through the respiratory chain. Note that fatty acid breakdown relates directly with oxygen uptake. For beta–oxidation to proceed, oxygen must be present to join with hydrogen. Without oxygen (anaerobic conditions), hydrogen remains joined with NAD+ and FAD bringing fat catabolism to a halt.

Total Energy Transfer From Fat CatabolismFor each 18-carbon fatty acid molecule, 147 molecules of ADP phosphorylate to ATP during

beta-oxidation and Krebs cycle metabolism. Because each triglyceride molecule contains three fatty acid molecules, 441 ATP molecules form from the triglyceride's fatty acid components (3 x 147 ATP). Also, 19 molecules of ATP form during glycerol breakdown, generating a total of 460 molecules of ATP for each triglyceride molecule catabolized. This represents a considerable energy yield because only a net of 36 ATP form during a glucose molecule's catabolism in skeletal muscle. The 40% efficiency of energy conservation for fatty acid oxidation amounts to a value similar to glucose oxidation efficiency.


INTENSITY AND DURATION AFFECT FAT USEFatty acid oxidation occurs during low intensity exercise. For example, fat combustion almost totally powers exercise at 25% of aerobic capacity. Carbohydrate and fat contribute energy equally during moderate exercise. Fat oxidation gradually increases as exercise extends to an hour or more and carbohydrates become depleted. Toward the end of prolonged exercise (with glycogen reserves low), circulating FFAs supply nearly 80% of the total energy required.

Figure 11. Protein-to-energy pathways.


ENERGY RELEASE FROM PROTEINProtein plays a contributory role as an energy substrate during endurance-type activities.

The amino acids (primarily the branched-chain amino acids leucine, isoleucine, valine, glutamine, and aspartate) first must convert to a form that readily enters pathways for energy release. This conversion requires removing nitrogen from the amino acid molecule. In this way, the muscle can directly use for energy the “carbon skeleton” by-products of donor amino acids. Only when an amino acid loses its nitrogen containing amino group can the remaining compound (usually one of the Krebs cycle's reactive compounds) contribute to ATP formation. Some amino acids are glucogenic; they yield intermediate products for glucose synthesis via gluconeogenesis. This gluconeogenic method serves as an important adjunct to provide glucose during prolonged exercise.

Figure 11 shows how protein supplies intermediates at three different levels that have energy producing capabilities. Like fat and carbohydrate, certain amino acids are ketogenic;

they cannot synthesize to glucose, but instead when consumed in excess

synthesize to fat. Amino acids that form pyruvate provide a carbon skeleton for glucose synthesis by the body, making protein a source for glucose when glycogen reserves run low.


The Metabolic MillThe Krebs cycle plays a more important role than simply degrading pyruvate produced

during glucose catabolism. Fragments from other organic compounds formed from fat and protein breakdown provide energy during the Krebs cycle.

The “metabolic mill” (Figure 12) depicts the Krebs cycle as the essential "connector" between energy from food macronutrients energy and chemical energy of ATP. The Krebs cycle also serves as a metabolic hub to provide intermediates to synthesize bionutrients for maintenance and growth. For example, excess carbohydrates provide the glycerol and acetyl fragments to synthesize triglyceride. Acetyl–CoA also functions as the starting point for synthesizing cholesterol and many hormones. In contrast, fatty acids do not contribute to glucose synthesis because pyruvate's conversion to acetyl-CoA does not reverse (notice the one-way arrow in Figure 12). Many of the carbon compounds generated in Krebs cycle reactions also provide the organic starting points for synthesizing nonessential amino acids. Amino acids, particularly alanine with carbon skeletons resembling Krebs cycle intermediates after deamination becomes synthesized to glucose.

Figure 12. The metabolic mill.


Fats Burn in a Carbohydrate FlameInterestingly, fatty acid breakdown depends in part on a continual background level of

carbohydrate breakdown. Recall that acetyl–CoA enters the Krebs cycle by combining with oxaloacetate to form citrate. Depleting carbohydrate decreases pyruvate production during glycolysis. Diminished pyruvate further reduces Krebs cycle intermediates, slowing Krebs cycle activity. Fatty acid degradation in the Krebs cycle depends on sufficient oxaloacetate availability to combine with the acetyl-CoA formed during b-oxidation. When carbohydrate level decreases, the oxaloacetate level may become inadequate. In this sense, “fats burn in a carbohydrate flame.”

MACRONUTRIENTS IN EXCESS READILY CONVERT TO FATExcess energy intake from any fuel source can be counterproductive. Too much of any

macronutrient results in accumulation of body fat. Surplus dietary carbohydrate first fills the glycogen reserves. Once these reserves fill, excess carbohydrate converts to triglycerides for storage in adipose tissue. Excess dietary calories as fat move easily into the body’s fat deposits as does any protein excess. Excess amino acids readily convert to fat.

FOR YOUR INFORMATIONEXCESS PROTEIN ACCUMULATES FATAthletes and others who believe that taking protein supplements add to muscle beware. Extra protein consumed above what the body requires ends up as body fat. If an athlete desires to become fat, excessive protein intake achieves this end. A protein excess does not contribute to the synthesis of muscle tissue.


LECTURE #5 WORKBOOKDefine Key Terms and Concepts

1. Adenosine triphosphatase

2. Aerobic

3. Amino acid

4. Anaerobic

5. Coupled reactions

6. Enzymes

7. Free fatty acids

8. Glycerol

9. Glycolysis

10.High-energy phosphate

11.Krebs Cycle

12.Lactate


13.Metabolic mill

14.Muscle glycogen

15.PCr

16.Pyruvate

17.The metabolic mill

STUDY QUESTIONS

ATP and Phosphate Bond Energy

ATP – The Energy CurrencyComplete the reaction:

ATP + H2O –––––––––>

ATP: A Limited CurrencyComplete the following two equations.

ATP + H2O ––––––––>

PCr + H2O ––––––––>

Phosphocreatine (PCr): The Energy ReservoirWhat main function does PCr play in energy metabolism?

Cellular Oxidation


“For every reaction involving cellular oxidation, there is a reaction involving __________________”.

Electron TransportBriefly describe the main purpose of electron transport.

Oxidative PhosphorylationComplete the following chemical equation:

NADH + H+ + 3ADP + 3 P + 1/2 O2 –––––––>

Role of Oxygen in Energy Metabolism “The main role of oxygen in energy metabolism is to _______________________________________”.

Energy Release from CarbohydrateWrite the equation for the complete breakdown (hydrolysis) of one mole of glucose.

Anaerobic versus AerobicThe two stages of carbohydrate breakdown are called ________________________ and _________________________.

Anaerobic Energy from Glucose: Glycolysis (Glucose Splitting)Glycolysis occurs in what part of the cell?

Formation of Lactic AcidWrite the chemical formula for lactic acid.

Aerobic Energy From Glucose: The Krebs cycleGive the most important function of the Krebs cycle.

Net Energy Transfer From Glucose Catabolism

Give the total ATP from glucose catabolism.


Energy Release From FatComplete the following equation:

Triglyceride + 3H2O –––––––––>

Breakdown of Glycerol and Fatty AcidsWhich substance, glycerol or fatty acid, undergoes beta oxidation?

GlycerolHow many molecules of ATP synthesize when one glycerol molecule breaks down?

Fatty AcidsOf what importance is oxygen in fatty acids catabolism?

Total Energy Transfer From Fat CatabolismHow many molecules of ATP become synthesized in the complete combustion of a neutral fat molecule?

Energy Release From ProteinAfter nitrogen removal from an amino acid, what happens to the remaining “carbon skeleton” in energy metabolism?

The Metabolic MillWhy is the Krebs cycle so important?

Fats Burn in a Carbohydrate FlameExplain why “fats burn in a carbohydrate flame.”

Excess Macronutrients Convert To FatCan protein consumed in excess of the body’s energy requirement end up as stored fat? Explain.


LECTURE #6ENERGY TRANSFER DURING EXERCISE

IntroductionThree major factors affect differences in the magnitude of energy transfer capacity: Body size and body composition Physical fitness Duration and intensity of exerciseIn sprint running, cycling, and swimming, energy output can increase 120 times above

resting metabolism. In contrast, during less intense but sustained marathon running, for example, energy requirements still exceed the resting level by 20 to 30 times. This chapter explains how the body’s diverse energy systems interact during rest and different exercise intensities.


Immediate Energy: The ATP-CP SystemPerformances of short duration and high intensity such as the 100-meter sprint, 25-meter

swim, smashing a tennis ball during the serve, or thrusting a heavy weight upwards require an immediate and rapid energy supply. The high-energy phosphates adenosine triphosphate (ATP) and phosphocreatine (PCr) stored within muscles almost exclusively provide this energy. The term phosphagens identifies these intramuscular energy sources.

Each kilogram of skeletal muscle stores approximately 5 millimoles (mmol) of ATP and 15 mmol of PCr. For a person with 30 kg of muscle mass, this amounts to between 570 and 690 mmol of phosphagens. If physical activity activates 20 kg of muscle, then stored phosphagen energy could power a brisk walk for 1 minute, a slow run for 20 to 30 seconds, or all-out sprint running and swimming for about 6 to 8 seconds. In the 100-meter dash, for example, the body cannot maintain maximum speed for longer than this time, and the runner may actually slow down towards the end of the race. Thus, the quantity of intramuscular phosphagens significantly influences the ability to generate “all-out” energy for brief durations. The enzyme creatine kinase regulates the rate of phosphagen breakdown.

Although all movements require utilization of high-energy phosphates, many rely almost exclusively on generating energy rapidly from this “energy system.” For example, success in wrestling, weight lifting, routines in gymnastics, most field events such as discus, shot put, pole vault, hammer, and javelin, and baseball and volleyball require brief but all-out, maximal effort. For longer duration ice hockey, soccer, field hockey, lacrosse, and basketball, other energy sources continually replenish the muscles’ phosphagen stores. For this purpose, the stored carbohydrates, fats, and proteins supply the necessary energy to recharge the pool of high-energy phosphates.

Short-Term Energy: The Lactic Acid SystemThe intramuscular phosphagens must continually resynthesize rapidly for strenuous

exercise to continue beyond a brief period. In such intense exercise, intramuscular stored glycogen provides the source of energy to phosphorylate ADP during anaerobic glycogenolysis, forming lactic acid.

When oxygen supply (or utilization) becomes inadequate to accept all hydrogen formed in glycolysis, pyruvate converts to lactic acid (pyruvate + 2H –––––> lactic acid). This permits the continued and rapid formation of ATP by anaerobic, substrate-level phosphorylation. Anaerobic energy for ATP resynthesis from glycolysis can be viewed as “reserve fuel” that activates when the oxygen demand/oxygen supply ratio exceeds 1.00. This occurs during the last phase “kick” of a one-mile race. Anaerobic ATP production also becomes crucial during a 440-m run or 100-m swim, or in multiple-sprint sports like ice hockey, field hockey, and soccer. These activities require rapid energy that exceeds that supplied by the stored phosphagens. If the intensity of “all-out” exercise decreases (thereby extending exercise duration), lactic acid buildup correspondingly decreases.

BLOOD LACTATE ACCUMULATIONSome lactic acid continually forms, even under resting conditions. However, lactic acid

removal by heart muscle and non-active skeletal muscle balances its production, yielding no net lactic acid build-up. Only when lactic acid removal does not match production does blood lactate begin to accumulate. Aerobic training produces cellular adaptations that allow for higher rates of lactate removal, so accumulation occurs only at higher exercise intensities.

Figure 1 illustrates the general relationship between oxygen uptake (expressed as a percentage of maximum) and blood lactate level during light, moderate, and strenuous exercise in endurance athletes and untrained individuals. During light and moderate exercise in both groups, aerobic metabolism adequately meet energy demands. Non-active tissues rapidly oxidize any lactic acid formed. This permits blood lactate to remain fairly stable (i.e.,

Figure 1. Blood lactate concentration at different levels of exercise expressed as a percent of VO2max for endurance trained and untrained individuals.


no net blood lactate accumulates), even though oxygen uptake increases. In essence, ATP for muscular contraction comes from energy-generating reactions requiring the oxidation of hydrogen.

Lactate begins to rise exponentially at about 55% of the healthy, untrained person’s maximal capacity for aerobic metabolism (termed the VO2max). The usual explanation for increases in blood lactate in heavy exercise assumes a relative tissue hypoxia (lack of oxygen). With lack of oxygen, anaerobic glycolysis partially meets the energy requirement, but hydrogen release begins to exceed its oxidation down the respiratory chain. At this point, lactic acid forms as the excess hydrogen produced during glycolysis pass to pyruvate. Lactic acid

formation increases at progressively higher levels of exercise intensity when active muscle cannot meet the additional energy demands aerobically.As Figure 1 shows, trained individuals (dashed line) show a similar pattern of blood lactate accumulation, except for the point when blood lactate appearance sharply increases. The point of abrupt rise in blood lactate, known as the “blood lactate threshold” (also termed anaerobic threshold and onset of blood lactate accumulation, or OBLA), occurs at a higher percentage of an athlete’s aerobic capacity. This favorable metabolic response in the endurance athlete could result from genetic endowment (e.g., muscle fiber type distribution), specific local muscle adaptations with training that favor formation of less lactic acid and its more rapid removal

rate, or a combination of these factors.Research shows that endurance training significantly increases capillary density and the

size and number of mitochondria. The concentration of the various enzymes and transfer agents involved in aerobic metabolism also increases. Such alterations certainly enhance the cell’s capacity to generate ATP aerobically, particularly via fatty acid breakdown. These training adaptations also extend exercise intensity before the onset of blood lactate accumulation. For example, world-class endurance athletes can perform at sustained high exercise intensities that represent 85 to 90% of maximum capacity for aerobic metabolism.

The lactic acid formed in one part of an active muscle can be oxidized by other fibers in the same muscle or by less active neighboring muscle tissue. Lactate uptake by less active muscle fibers helps to depress blood lactate levels during light-to-moderate exercise and also provides an important means for glucose conservation in prolonged work.

Figure 2. Time course of oxygen uptake during continuous jogging at a relatively slow pace. The dots along the curve represent measured values of oxygen uptake.


Lactate-Producing CapacityCapacity to generate high levels of lactic acid during exercise enhances maximal power

output for short durations. Because tissues continually utilize lactate during exercise, blood lactate accumulation can significantly underestimate total blood lactate production. Ability to generate a high lactic acid concentration in maximal exercise increases with specific sprint and power training; detraining subsequently decreases this advantage.

Well-trained “anaerobic” athletes who perform maximally for brief periods generate blood lactate levels 20 to 30% higher than untrained individuals with similar exercise. Enhanced lactate-producing capacity with sprint-type training may result from improved motivation that often accompanies the trained state (i.e., the trained “push” themselves harder)and an approximate 20% increase in glycolytic enzyme activity.

Blood Lactate As An Energy SourceBlood lactate serves as substrate for glucose retrieval (gluconeogenesis) and as a direct

fuel source for active muscle. Tracer studies in muscle and other tissues show that lactate produced in fast-twitch muscle fibers can circulate to other fast-twitch or slow-twitch fibers for conversion to pyruvate. Pyruvate, in turn, converts to acetyl-CoA for entry to the Krebs cycle for aerobic energy metabolism. Such lactate “shuttling” between cells enables glycogenolysis in one cell to supply other cells with fuel for oxidation. This makes muscle not only a major site of lactate production, but also a primary tissue for lactate removal via oxidation.

Long-Term Energy: The Aerobic SystemAlthough glycolysis releases anaerobic energy rapidly, only a relatively small total ATP yield

results from this pathway. In contrast, aerobic metabolic reactions provide for the greatest portion of energy transfer, particularly when exercise duration extends longer than 2 to 3 minutes.

Oxygen Uptake During ExerciseThe curve in Figure 2

illustrates oxygen uptake during each minute of a relatively slow jog continued at a steady pace for 20 minutes. The vertical Y-axis indicates the use of oxygen by the cells (referred to as oxygen uptake or oxygen consumption); the horizontal X-axis displays exercise time. The abbreviation VO2

indicates oxygen uptake, where the V denotes the volume consumed; the dot placed above the V expresses oxygen uptake as a per minute value. Oxygen uptake during any minute can easily be determined by locating time on the X-axis and its corresponding point for oxygen uptake on the Y-

UofM

Figure 3. Oxygen uptake and deficit for trained and untrained individuals during submaximum cycle ergometer exercise. Both individuals reach the same steady-rate VO2 but the trained person reaches it at a faster rate, reducing the oxygen deficit.


axis. For example, after running four minutes, oxygen uptake equals approximately 1.6 mL•kg-

1•min-1. From the graph, oxygen uptake rises rapidly during the first minutes of exercise and

reaches a relative plateau between minutes three and six. Oxygen uptake then remains relatively stable throughout the remainder of exercise. The flat portion or plateau of the oxygen uptake curve represents the steady-rate of aerobic metabolism – a balance between energy required by working muscles and the rate of aerobic ATP production. Oxygen consuming reactions supply the energy for exercise during steady-rate; any lactic acid produced either oxidizes or reconverts to glucose in the liver, kidneys, and skeletal muscle. No accumulation of blood lactate occurs under these steady-rate metabolic conditions.

Many Levels of Steady-rateCertain steady-rate exercise levels for the endurance athlete could exhaust the untrained.

For some, lying in bed, working around the house, and playing an occasional round of golf represent the activity spectrum for which adequate oxygen maintains a steady-rate. A champion marathon runner, on the other hand, can run 26.2 miles in slightly more than 2 hours and still be in steady-rate! This sub-5-minute-per-mile pace represents a magnificent physiologic-metabolic accomplishment to maintain the required level of aerobic metabolism. Two of these crucial functional capacities consist of: (1) delivering adequate oxygen to active muscles, and (2) processing oxygen for aerobic ATP production.

Oxygen DeficitThe upward trending curve of oxygen uptake shown in Figure 2 and 3 does not increase instantaneously to a steady-rate at the start of exercise. Instead, it remains considerably below the steady-rate level in the first minute of exercise, even though the exercise energy requirement remains essentially unchanged throughout the activity period. The temporary “lag” in oxygen uptake occurs because ATP provides the muscle’s immediate energy requirement without the

FOR YOUR INFORMATIONLIMITED DURATION OF STEADY RATETheoretically, exercise could continue indefinitely if performed at a steady-rate of aerobic metabolism, if the person desired. However, factors other than motivation place a limit on the duration of steady-rate work. These include loss of body fluids in sweat and depletion of essential nutrients, especially blood glucose and glycogen stored in liver and active muscle.


need for oxygen. Oxygen becomes important in subsequent energy transfer reactions to serve as an electron acceptor to combine with the hydrogen produced during: Glycolysis Beta- oxidation of fatty acids Krebs cycle reactions

Thus, a deficit always exists in the oxygen uptake response to a new, higher steady-rate level, regardless of activity or exercise intensity.

The oxygen deficit quantitatively represents the difference between the total oxygen actually consumed during exercise and the amount that would have been consumed had a steady-rate, aerobic metabolism occurred immediately when exercise began. Energy provided during the deficit phase of exercise represents a predominance of anaerobic energy transfer. Stated in metabolic terms, oxygen deficit represents the quantity of energy produced from stored intramuscular phosphagens plus energy contributed from rapid glycolytic reactions that yield phosphate-bond energy until oxygen uptake and energy demands reach the steady rate.

Oxygen Deficit in Trained and UntrainedFigure 3 shows the oxygen uptake response to submaximum cycle ergometer exercise for a

trained and untrained person. Similar values for steady-rate oxygen uptake during light and moderate exercise generally occur in trained and untrained individuals. The trained person, however, reaches the steady-rate quicker; hence, this person has a smaller oxygen deficit for the same exercise duration compared to the untrained person. This means a greater total oxygen consumed during exercise for the trained person, with a proportionately smaller anaerobic component of energy transfer. A likely explanation for the differences in oxygen deficit between trained and untrained individuals relates to a more highly developed aerobic bioenergetic capacity of the trained person. An augmented aerobic capacity results from either improved central cardiovascular function or training-induced local muscular adaptations known to increase a muscle’s capacity to generate ATP aerobically. These adaptations would cause earlier aerobic ATP production in exercise with less lactic acid formation for the trained person.

Maximal Oxygen Uptake (VO2max)Figure 4 depicts the curve for oxygen uptake during a series of constant-speed runs up six

hills, each progressively steeper than the next. The laboratory simulates these “hills” by increasing the elevation of a treadmill, raising the height of a step bench, or providing greater resistance to pedaling a bicycle ergometer. Each successive hill (equivalent to an increase in exercise intensity, or load) requires greater energy output, and thus an additional demand for aerobic metabolism. Increases in oxygen uptake relate linearly and in direct proportion to exercise intensity during the climb up the first several hills. Although the runner maintains speed up the last two hills, oxygen uptake does not increase the same magnitude as with prior hills. No increase in oxygen uptake occurs during the run up the last hill. The maximal oxygen uptake or simply VO2max describes the region where oxygen uptake plateaus and shows no further increase (or increases only slightly) despite additional increase in exercise intensity. The VO2max holds great physiological significance because of its dependence on the functional capacity and integration of the systems required for oxygen supply, transport, delivery, and utilization.

Figure 4. Attainment of maximal oxygen uptake while running up hills of increasing slope. VO2max occurs in the region where a further increase in exercise intensity does not produce an additional increase in oxygen uptake.


The VO2max provides a good indication of an individual’s capacity for aerobically resynthesizing ATP. Exercise performed above VO2max can only take place by energy transfer predominantly from anaerobic glycolysis with lactic acid formation. Under such conditions, performance deteriorates and the individual cannot continue at that intensity. The large build

up of lactic acid, due to the additional anaerobic muscular effort, disrupts the already high rate of energy transfer for the aerobic resynthesis of ATP. To borrow an analogy from business economics: supply (aerobic resynthesis of ATP) fails to meet demand (energy required for muscular effort). An aerobic energy supply-demand imbalance affects production (lactic acid accumulates) and compromises exercise performance.

The Energy Spectrum of

ExerciseFigure 5 depicts the relative contributions of anaerobic and aerobic energy sources during

various durations of maximal exercise. The data represent estimates from experiments of all-out treadmill running and bicycling, they can relate to other activities by drawing the appropriate time relationships. For example, a 100-m sprint run equates to any all-out activity lasting about 10 s, while an 800-m run lasts approximately 2 minutes. All-out exercise for one

minute includes the 400-m dash in track, the 100-m swim, and multiple full-court presses during a basketball game.

Intensity and Duration Determine the Blend

The body's energy transfer systems should be viewed along a continuum in terms of exercise bioenergetics. Anaerobic sources supply most of the energy for fast movements, or during increased resistance to movement at a given speed. Also, when movement begins at either fast or slow speed (from performing a front handspring to starting a marathon run), the intramuscular phosphagens provide immediate anaerobic energy for the required muscle action.

Figure 5. Relative contribution of aerobic and anaerobic energy metabolism during maximal physical effort of various durations; 2 min requires about 50% of the energy from both aerobic and anaerobic processes. At world-class 4-min mile pace, aerobic metabolism supplies approximately 65% of the energy, with the remaining from anaerobic processes.

Figure 6. Oxygen uptake during exercise and recover from (A) lightsteady-rate exercise and (B) moderate to heavy steady-rate exercise.

Figure 6. Oxygen uptake during exercise and recovery from light steady-rate exercise.


At the short-duration extreme of maximum effort, the intramuscular phosphagens ATP and PCr supply the major energy for the entire exercise. The ATP-PCr and lactic acid systems provide about one-half of the energy required for “best-effort“ exercise lasting 2 minutes, whereas aerobic reactions provide the remainder. For top performance in all-out, 2-minute exercise, a person must possess a well-developed capacity for both aerobic and anaerobic metabolism. Intense exercise of intermediate duration performed for 5 to 10 minutes, like middle-distance running and swimming or stop-and-go sports like basketball and soccer, produces a greater demand for aerobic energy transfer. Longer duration marathon running, distance swimming and cycling, recreational jogging, cross-country skiing, and hiking and backpacking require a continual energy supply derived aerobically without reliance on lactic acid formation.

Intensity and duration determine which energy system and metabolic mixture predominate during exercise. The aerobic system predominates in low intensity exercise with fat serving as the primary fuel source. The liver markedly increases its release of glucose to active muscle as exercise progresses from low to high intensity. Simultaneously, glycogen stored within muscle serves as the predominant carbohydrate energy source during the early stages of exercise and when exercise intensity increases. During high-intensity aerobic exercise, the advantage of selective dependence on carbohydrate metabolism lies in its two times more rapid energy transfer capacity compared to fat and protein fuels.

Compared to fat, carbohydrate also generates about 6% greater energy per unit oxygen consumed. As exercise continues and muscle glycogen depletes, progressively more fat (intramuscular triglycerides and circulating FFA) enters the metabolic mixture for ATP production. In maximal anaerobic effort (reactions of glycolysis), carbohydrate becomes the sole contributor to ATP production.

A sound approach to exercise training analyzes an activity for its specific energy components and then establishes a training regimen to improve those systems that assure optimal physiologic and metabolic adaptations. An improved capacity for energy transfer usually translates into improved exercise performance.

Excess Post-Exercise Oxygen Consumption: The So-Called “Oxygen Debt”

Bodily processes do not immediately return to resting levels after exercise ceases. In light exercise (e.g., golf, archery, bowling), recovery to a resting condition takes place rapidly and is often unnoticed. With particularly intense physical activity (running full speed for 800 m or trying to swim 200 m as fast as possible), however, it takes considerable time for the body to return to resting levels. The difference in recovery from light and strenuous exercise relates largely to the specific metabolic and physiologic processes in each form of exercise.

A.V. Hill (1886-1977), the British Nobel physiologist (see Lecture 2), referred to oxygen uptake during recovery as the “oxygen debt.” Contemporary theory no longer uses this term. Instead, recovery oxygen uptake or excess post-exercise oxygen consumption (EPOC) defines the excess oxygen uptake above the resting level in recovery. Regardless of the term used, the meaning refers to the total oxygen consumed following exercise in excess of a pre-exercise baseline level.

Figure 6 shows that light exercise produces a rapid attainment of steady-rate and a small oxygen deficit. Rapid recovery ensues from such exercise with an accompanying small EPOC. In moderate to heavy aerobic exercise would take longer to reach steady-rate and the oxygen deficit would become larger compared to light exercise.


Oxygen uptake in recovery from more strenuous exercise returns more slowly to the pre-exercise resting level. There occurs an initial rapid decline in recovery oxygen uptake (similar to recovery from light exercise) followed by a more gradual decline to baseline.

Metabolic Dynamics of Recovery Oxygen UptakeCurrent understanding of the specific chemical dynamics in exhaustive exercise does not

permit a precise biochemical partitioning of EPOC, especially in terms of lactic acid.No doubt exists that the elevated aerobic metabolism in recovery contributes to restoring

the body’s processes to pre-exercise conditions. Oxygen uptake following light and moderate exercise replenishes high-energy phosphates depleted in the preceding exercise. In recovery from strenuous exercise, some oxygen resynthesizes a portion of lactic acid to glycogen. However, a significant portion of recovery oxygen uptake supports physiologic functions actually taking place during recovery. The considerably larger recovery oxygen uptake compared to oxygen deficit with high-intensity, exhaustive exercise results from factors such as elevated body temperature. Core temperature frequently increases by about 3ºC (5.4ºF) during vigorous exercise, and can remain elevated for several hours into recovery. This thermogenic “boost” directly stimulates metabolism and increase EPOC.

In essence, all of the physiologic systems activated to meet the demands of muscular activity increase their own need for oxygen during recovery. The recovery oxygen uptake reflects:

Anaerobic metabolism of previous exercise Respiratory, circulatory, hormonal, ionic, and thermal adjustments during recovery as a

consequence of prior exercise

Active Versus Passive RecoveryProcedures for speeding recovery from exercise can be categorized as active or passive.

Active recovery (often called “cooling-down” or “tapering-off”) involves submaximum aerobic exercise performed immediately after the exercise. Many believe that continued movement prevents muscle cramps, stiffness, and facilitates the recovery process. In contrast, in passive recovery a person usually lies down assuming that complete inactivity reduces the resting energy requirements and “frees” oxygen for the recovery process. Modifications of active and passive recovery have included the use of cold showers, massages, specific body positions, ice application, and ingesting cold fluids. Research findings have shown ambiguous results for many of these recovery procedures.

FOR YOUR INFORMATIONCAUSES OF EXCESS POST EXERCISE OXYGEN CONSUMPTION (EPOC) WITH HEAVY EXERCISE

Resynthesis of ATP and PCr Rsynthesize blood lactate to glycogen Oxidize blood lactate in energy metabolism Restore oxygen to blood, tissue fluids and myoglobin Thermogenic effects of elevated core temperature Thermogenic effects of hormones (catecholamines) Increase in pulmonary and circulatory dynamics


Optimal Recovery From Steady-rate ExerciseMost people can perform exercise below 55 to 60% of VO2max in steady-rate with little blood

lactate accumulation. Recovery from such exercise resynthesizes high-energy phosphates, replenishes oxygen in the blood, body fluids, and muscle myoglobin, and has a small energy cost to sustain circulation and ventilation. Passive procedures produce the most rapid recovery in such cases because exercise would only serve to elevate total metabolism and delay recovery.

Optimal Recovery from Non Steady-rate ExerciseLactic acid formation exceeds its rate of removal and blood lactate accumulates when

exercise intensity exceeds maximum steady-rate. As work intensity increases, lactate levels rise sharply and the exerciser soon becomes exhausted. Although the precise mechanisms of fatigue during intense anaerobic exercise are not fully understood, the blood lactate level does provide an objective indication of the relative strenuousness of exercise and reflects the adequacy of the recovery process.

Active aerobic exercise in recovery accelerates lactic acid removal. The optimal level of exercise in recovery ranges between 30 and 45% of VO2max for bicycle exercise, and 55 to 60% of VO2max when recovery involves treadmill running. The variation between these two forms of exercise probably results from the more localized nature of bicycling (i.e., more intense effort per unit muscle mass), which produces a lower lactate threshold compared to running.

FOR YOUR INFORMATIONKEEP MOVING IN RECOVERY FROM HEAVY EXERCISEActive recovery facilitates lactate removal because of increased perfusion of blood through “lactate-using” organs like the liver and heart. In addition, increased blood flow through the muscles in active recovery certainly enhances lactate removal because muscle tissue oxidizes this substrate during Krebs cycle metabolism.


LECTURE #6 STUDY GUIDEDefine Key Terms and Concepts

1. Criteria for VO2max

2. EPOC

3. Ergometer

4. Fast-twitch fibers

5. Immediate energy system

6. Lactic Acid

7. Long–term energy system

8. Maximal oxygen uptake

9. Oxygen debt

10.Oxygen uptake

11.Short–term energy system

12.Slow–twitch fibers


13.Steady-rate

STUDY QUESTIONS

Immediate Energy: The ATP-CP SystemIndicate the quantity of ATP and PCr stored within the body’s muscles.

ATP

PCr

Indicate the duration of a brisk walk, a slow run, and an all-out sprint that the intramuscular high-energy phosphates powers.

Brisk walk

Slow run

All-out sprint

Short-Term Energy: The Lactic Acid SystemList three activities powered primarily by the lactic acid energy system.

1. 3.

2.

Blood Lactate AccumulationGive a reasonable explanation why blood lactate accumulates during exercise.

Lactate-Producing CapacityHow much more blood lactate can a sprint/power trained athlete accumulate compared to an untrained counterpart?

Oxygen Uptake During Exercise


Draw and label the curve for oxygen uptake during 10 minutes of moderate running exercise. Indicate the area of oxygen deficit and the area of steady-rate.

Express oxygen uptake in relation to body mass (mL•kg-1•min-1)for an individual who weighs 85 kg and consumes 2.0 L•min-1 of oxygen during jogging.

Many Levels of Steady-rateWhat two metabolic-physiologic factors determine a person’s ability to perform exercise at a steady-rate?

1.

Time, min

Oxy

gen

upta

ke, L

•min

-1


2.

Oxygen deficitDefine the oxygen deficit

Oxygen Deficit in Training and UntrainedDo trained or untrained or untrained reach steady-rate faster?

Maximal Oxygen Uptake (VO2max)Draw and label the oxygen uptake curve during exercise of progressively increasing work intensity (every 3 min) to exhaustion. Indicate the VO2max.

The Energy Spectrum of ExerciseWhat two factors determine which energy system and metabolic mixture are used during exercise.

Exercise Intensity


1.

2.

Excess Post-Exercise Oxygen Consumption: The So-Called “Oxygen Debt”Draw and label the oxygen uptake curves during recovery from light, steady-rate exercise and exhaustive exercise. Include the fast the slow component of the recovery where applicable.

Metabolic Dynamics of Recovery Oxygen UptakeGive two factors that reflect the recovery oxygen uptake1.

2.

Optimal Recovery From Steady-rate ExerciseWhat procedures optimize recovery from steady-rate exercise?

Time

Rest Exercise Recovery


LECTURE #7EVALUATING ENERGY-GENERATING CAPACITIES

IntroductionIn this lecture, I will discuss the capacity of the various energy transfer systems discussed

previously, with special reference to measurement, specificity, and individual differences.We all possess the capability for anaerobic and aerobic energy metabolism, although

the capacity for each form of energy transfer varies considerably among individuals. These differences among individuals underlie the concept of individual differences in metabolic capacity for exercise. A person’s capacity for energy transfer (and for many other physiologic functions) does not exist as some general factor for all types of exercise, but depends largely on the exercise mode used for training and evaluation. A high maximum oxygen uptake in running, for example, does not necessarily assure a similar aerobic power when activating different muscle groups as in swimming and rowing. This disparity represents an example of specificity of metabolic capacity. On the other hand, some individuals with high aerobic power in one form of exercise also possess an above average aerobic power in other diverse activities. This illustrates the generality of metabolic capacity. For the most part, more specificity exists than generality in metabolic and physiologic function.

Lecture Objectives Explain specificity and generality as they apply to exercise. Describe procedures to administer two practical “field tests” to evaluate power output

capacity of the high-energy intramuscular phosphates (immediate energy system). Describe a commonly used test to evaluate the power output capacity of glycolysis (short-

term energy system). Define maximal oxygen uptake (VO2max), including the physiological significance of this

aerobic fitness measure. Describe a graded exercise test. List criteria that indicate when a person reaches a “true” VO2max during a graded exercise

test. Explain how each of the following affect maximal oxygen uptake: (1) mode of exercise, (2)

heredity, (3) state of training, (4) gender, (5) body composition, and (6) age.

Figure 1. Three energy systems and their percentage contribution (Y-axis) to total energy output during all-out exercise of different durations (X-axis).


Overview of Energy Transfer Capacity During ExerciseThe immediate and short-term energy systems mainly power all-out exercise for up to 2-

minutes duration. Both systems operate anaerobically because their transfer of chemical energy does not require oxygen (refer to lecture 6.) Generally, fast movements or resistance to movement at a given speed place great reliance on anaerobic energy transfer. Figure 1 shows the relative involvement of the anaerobic and aerobic energy transfer systems for different durations of all-out exercise.

At the initiation of either high- or low-speed movements, the intramuscular phosphagens, ATP and PCr, provide immediate and nonaerobic energy for muscle action. After the first few seconds of movement, the glycolytic energy system provides an increasingly greater proportion of the total energy. For exercise to continue, although at a lower intensity, a progressively greater demand becomes placed on the aerobic metabolic pathways of ATP resynthesis.

Some activities require the capacity of more than one energy transfer system, whereas other activities rely predominately on a single system. However, all activities activate each energy system to some degree, depending on exercise intensity and duration. Of course, the greater demand for anaerobic energy transfer occurs for higher intensity, shorter duration activities.

Anaerobic Energy: The Immediate and Short-Term Energy Systems

Evaluation of the Immediate Energy SystemPerformance tests that rely on maximal activation of the intramuscular ATP-PCr energy

reserves have been developed as “field tests” to evaluate the immediate energy transfer system. These maximal effort performances, generally referred to as power tests, evaluate the time-rate of doing work (i.e., work accomplished per unit time). The following formula

computes power output:where, F equals force generated, D equals distance through which the force moves, and T equals exercise duration.

P = F x DT


Watts represents a common expression of powerOne watt equals 0.73756 ft-lb•sec–1 or 6.12 kg-m•min–1

STAIR-SPRINTING POWER TESTS

Researchers have measured short-term power by sprinting up a flight of stairs. Figure 2 shows a subject running up a staircase as fast as possible taking three steps at a time. The external work performed equals the total vertical distance the body rises up the stairs; for six stairs this distance usually equals about 1.05 meters.

The power output for a 65-kg woman who traverses six steps in 0.52 seconds computes as follows:

F = 65 kg; D = 1.05 m; T = 0.52 sPower = [65 kg x 1.05 m] ÷ 52 s

Power = 131.3 kg-m•s-1 (1287 watts)Because body mass greatly influences the power-output score in stair sprinting, a heavier

person necessarily generates greater power at the same speed as a lighter person who covers the same vertical distance. Because of the influence of body mass, use caution in interpreting differences in stair-sprinting power scores and making inferences about individual differences in ATP-PCr energy capacity. The test may be better suited for evaluating individuals of similar body mass, or the same people before and after a specific training regimen.

Figure 2. Stair-sprinting power test. The subject begins at point A and runs as fast as possible up a flight of stairs, taking 3 steps at a time. Electric switch mats placed on the steps record the time to cover the distance between stair 3 and 9 to the nearest 0.01 s. Power output equals the product of the subject’s mass (F) and vertical distance covered (D), divided by the time (T).


Jumping-Power TestsFor years, physical fitness test batteries have included jumping tests such as the jump-and-

reach test or a standing broad jump. The jump-and-reach test score equals the difference between a person’s standing reach and the maximum jump-and-touch height. For the broad jump, the score represents the horizontal distance covered in a leap from a semicrouched position. Although both tests purport to measure leg power, they probably fail to achieve this goal. For one thing, with jump tests, power generated in propelling the body from the crouched position occurs only in the time the feet contact the floor's surface. This brief period cannot sufficiently evaluate a person’s ATP and PCr power capacity.

OTHER POWER TESTS

A 6 to 8-second performance involving all-out exercise measures the person’s capacity for immediate power from the intramuscular high-energy phosphates (refer to Figure 1). Examples of other such tests include sprint running or cycling, shuttle runs and more localized movements such as arm cranking or simulated stair climbing, rowing, or skiing. In the popular Quebec 10-second test of leg cycling power, the subject performs two all-out 10-second rides at a frictional resistance equal to 0.09 kg per kg of body mass, with 10- minutes rest between exercise bouts. Exercise begins by pedaling as fast as possible as the friction load is applied and continues all-out for 10 seconds. Performance represents the average of the two tests reported in peak joules per kg of body weight, and total joules per kg of body weight.

Power tests may be used to show changes in an athlete’s performance with specific training. Such tests also serve as an excellent means for self-testing and motivation, and provide the actual movement-specific exercise for training the immediate energy system. Many football teams, for example, routinely use the 40-yard dash as a criterion to evaluate a player’s speed. Although many types of “speed” need to be evaluated in football, the 40-yard scores may provide useful information for player evaluation. It should be emphasized, however, that research needs to establish how 40-yard speed in a straight line relates to overall football ability for players at similar positions. A run test of shorter duration (up to 20 yd), or one with frequent changes in direction, may be an equal or more suitable performance measure.

Several physiologic and biochemical measures, in addition to exercise performance, can estimate the energy-generating capacity of the immediate energy system. These include:

Size of the intramuscular ATP-PCr pool ATP and PCr depletion rates from all-out exercise of short duration Magnitude of the oxygen deficit calculated from the oxygen uptake curve Magnitude of the alactic (fast component) portion of recovery oxygen uptake

FOR YOUR INFORMATIONINTERCHANGEABLE EXPRESSIONS FOR ENERGY AND WORK1 foot-pound (ft-lb) = 0.13825 kilogram-meters (kg-m)1 kg-m = 7.233 ft-lb = 9.8066 joules1 kilocalorie (kcal) = 3.0874 ft-lb = 426.85 kg-m = 4.186 kilojoules (kJ)1 Joule (J) = 1 Newton-meter (Nm)1 kilojoule (kJ) = 1000 J = 0.23889 kcal


Evaluation of the Short-Term Energy SystemAs displayed in Figure 1, the anaerobic reactions of glycolysis (short-term energy system)

generate increasingly greater energy for ATP resynthesis when all-out exercise continues longer than a few seconds. This does not mean that aerobic metabolism remains unimportant at this stage of exercise, or that the oxygen-consuming reactions have not been “switched-on.” To the contrary, Figure 2 reveals an increase occurs in aerobic energy contribution very early in exercise. However, the energy requirement in all-out exercise significantly exceeds energy generated by hydrogen's oxidation in the respiratory chain. This means that the anaerobic reactions of glycolysis predominate, with large quantities of lactic acid accumulating within the active muscle and ultimately appearing in the blood.

Unlike tests for maximal oxygen uptake, no specific criteria exist to indicate that a person has reached a maximal anaerobic effort. In fact, one's level of self-motivation, including external factors in the test environment, likely influences the test score. Researchers most commonly use the level of blood lactate to indicate the degree of activation of the short-term energy system.

Performance Tests of Glycolytic PowerActivities that require substantial activation of the short-term energy system demand

maximal work for up to three minutes. All-out runs and cycling exercise have usually been used, although weight lifting (repetitive lifting of a certain percentage of maximum) and shuttle and agility runs have also been used. Because age, sex, skill, motivation, and body size affect maximal physical performance, difficulty exists selecting a suitable criterion test for developing normative standards for glycolytic energy capacity. A test that maximally uses only the leg muscles cannot adequately assess short-term anaerobic capacity for upper-body exercise such as rowing or swimming. Within the framework of exercise specificity, the performance test must be similar to the activity or sport for which the energy capacity is being evaluated. In most cases, the actual activity serves as the test.

Figure 3 presents the relative contribution of each metabolic pathway during three different duration all-out cycle ergometer tests. The results are shown as a percent of the total work output. Note the progressive change in the percentage contribution of each of the energy systems to the total work output as duration of effort increases.


Blood Lactate LevelsBlood lactate levels remain relatively low during steady-rate exercise up to about 55% of the

VO2max. Thereafter, blood lactate begins to accumulate, with a precipitous increase noted in the region of the VO2max.

Glycogen DepletionBecause the short-term energy system largely depends on glycogen stored in the specific

muscles activated by exercise, these muscles' pattern of glycogen depletion provides an indication of the contribution of glycolysis to exercise.

10 sec 30 sec 90 sec

Short-duration tests

Figure 3. Contribution of each of the energy systems to the total work accomplished in three tests of short-duration.

Figure 4. Glycogen depletion from the vastus lateralis portion of the quadriceps femoris muscle in bicycle exercise of different intensities and durations. Exercise at 31% of VO2max (the lightest workload) caused some depletion of muscle glycogen, but the most rapid and largest depletion occurred with exercise that ranged from 83% to 150% of VO2max.


Figure 4 shows that the rate of glycogen depletion in the quadriceps femoris muscle during bicycle exercise closely parallels exercise intensity. With steady-rate exercise at about 30% of VO2max, a considerable reserve of muscle glycogen remains, even after cycling for 180 minutes. Because relatively light exercise relies mainly on a low level of aerobic metabolism, large quantities of fatty acids provide energy with only moderate use of stored glycogen. The most rapid and pronounced glycogen depletion occurs at the two heaviest workloads. This makes sense from a metabolic standpoint because glycogen provides the only stored nutrient for anaerobic ATP resynthesis. Thus, glycogen has high priority in the “metabolic mill” during strenuous exercise.

Changes in total muscle glycogen as illustrated in Figure 4 may not give a precise indication of the degree of glycogen

breakdown in specific muscle fibers, however. Depending on exercise intensity, glycogen depletion occurs selectively in either fast- or slow-twitch fibers. For example, during all-out one-minute sprints on a bicycle ergometer, activation of the fast-twitch fibers provides the predominant power for the exercise. Glycogen content in these fibers becomes almost totally depleted because of the sprint's anaerobic nature. In contrast, slow-twitch fibers become glycogen-depleted early during moderate to heavy prolonged aerobic exercise. Glycogen utilization (and depletion) mainly in specific muscle type fibers makes it difficult to evaluate the degree of glycolytic activation from changes in a muscle’s total glycogen content before and after exercise.

Anaerobic Energy Transfer CapacityDifferences in training level, capacity to buffer acid metabolites produced in heavy exercise,

and motivation contribute to individual differences in capacity to generate short-term anaerobic energy.

Figure 5. Maximal oxygen uptake of male and female Olympic-caliber athletes in different sport categories compared to healthy sedentary subjects.


Effects of TrainingShort-term supermaximal exercise on a bicycle ergometer in trained subjects always

produces higher levels of blood and muscle lactic acid, and greater muscle glycogen depletion. For all subjects, better performances are usually associated with higher blood lactate levels. These results support the belief that training for brief, all-out exercise enhances the glycolytic system's capacity to generate energy. In sprint and middle-distance activities, individual differences in anaerobic capacity account for much of the variation in exercise performance.

Buffering of Acid MetabolitesLactic acid accumulates when anaerobic energy transfer predominates. This causes an

increase in the muscle's acidity, negatively affecting the intracellular environment. The deleterious intracellular alterations during anaerobic exercise have caused speculation that anaerobic training might enhance short-term energy capacity by increasing the body’s buffering reserve to enable greater lactic acid production through more effective buffering. However, only a small increase in alkaline reserve has been noted in athletes compared to sedentary individuals. Thus, the general consensus is that trained people have similar buffering capability as untrained individuals.

MotivationIndividuals with greater

“pain tolerance,” “toughness,” or ability to “push” beyond the discomforts of fatiguing exercise definitely accomplish more anaerobic work. These people usually generate greater levels of blood lactate and glycogen depletion; they also score higher on tests of short-term energy capacity. Although difficult to categorize and quantify, motivation plays a key role in superior performance at all levels of competition.

Aerobic Energy: The Long-Term Energy System

The data in Figure 5 illustrate that persons who engage in sports that require sustained, high-intensity exercise (i.e., endurance) generally possess a large aerobic energy transfer capacity. Men and women who compete in distance running, swimming,


bicycling, and cross-country skiing generally record the highest maximal oxygen uptakes. These athletes have almost twice the aerobic capacity as sedentary individuals. This does not mean that only VO2max determines endurance exercise capacity. Other factors, especially those at the muscle level such as capillary density, enzymes, and fiber type, strongly influence the capacity to sustain a high percentage of VO2max. However, the VO2max does provide useful information about the capacity of the long-term energy system. Attainment of VO2max requires integration of ventilatory, cardiovascular, and neuromuscular systems; this gives significant physiologic “meaning” to this metabolic measure. For these reasons, VO2max represents a fundamental measure in exercise physiology and often serves as the standard against which to compare performance estimates of aerobic capacity and endurance fitness.

Measurement of Maximal Oxygen UptakeTests for VO2max use exercise tasks that activate large muscle groups with sufficient intensity

and duration to engage maximal aerobic energy transfer. Exercise includes treadmill walking or running, bench stepping, or cycling. VO2max has also been measured during free, tethered, and flume swimming and swim-bench ergometry, and simulated rowing, skiing, stair climbing, as well as ice skating and arm-crank exercise. Considerable research effort has been directed toward (1) development and standardization of tests for VO2max, and (2) establishment of norms related to age, sex, state of training, and body composition.

Criteria for VO2max

A leveling-off, or peaking-over, in oxygen uptake during increasing exercise intensity signifies attainment of maximum capacity for aerobic metabolism (i.e., a “true” VO2max). When this generally accepted criterion is not met, or local muscle fatigue in the arms or legs rather than central circulatory dynamics limits test performance, the term “peak oxygen uptake” (VO2peak) usually describes the highest oxygen uptake value during the test.

Tests of Aerobic PowerNumerous tests have been devised and standardized to measure VO2max. These test

performances should be independent of muscle strength, speed, body size, and skill, with the exception of specialized swimming, rowing, and ice skating tests.

The VO2max test may require a continuous 3- to 5-minute “supermaximal” effort, but it usually consists of increments in exercise intensity (referred to as a graded exercise test or GXT) until the subject stops. Some researchers have imprecisely termed this end point “exhaustion,” but it should be kept in mind that the subject terminates the test (for whatever reason). A variety of psychological or motivational factors can influence this decision, and it may not reflect true physiologic exhaustion. It can take considerable urging and prodding to get subjects to the point of acceptable criteria for VO2max, particularly individuals unaccustomed to producing maximal exercise. Children and adults encounter particular difficulty if they have had little prior experience performing strenuous exercise. Practical experience has shown that attaining a plateau in oxygen uptake during the VO2max test requires high motivation and a relatively large anaerobic component.

Factors That Affect Maximal Oxygen UptakeOf the many factors influencing VO2max, the most important include mode of exercise and the

person’s heredity, training state, sex, body composition, and age.

Mode of ExerciseVariations in VO2max during different modes of exercise reflect the quantity of muscle mass

activated during the performance. In experiments that determined VO2max on the same subjects during exercise, treadmill exercise produced the highest values. Bench stepping, however, has


generated VO2max scores identical to treadmill values and significantly higher than values on a bicycle ergometer. With arm-crank exercise, aerobic capacity reaches only about 70% of one’s treadmill VO2max.

The treadmill represents the laboratory apparatus of choice for determining VO2max in healthy subjects. The treadmill provides easy quantification and regulation of exercise intensity. Compared with other forms of exercise, subjects achieve one or more of the criteria for establishing VO2max more easily on the treadmill. Bench stepping or bicycle exercise is suitable alternatives under non-laboratory “field” conditions.

HeredityA question frequently raised concerns the relative contribution of natural endowment to

physiologic function and exercise performance. For example, to what extent does heredity determine extremely high aerobic capacities of the endurance athletes? Do these exceptionally high levels of functional capacity reflect more than the training effect? Although the answer remains incomplete, some researchers have focused on the question of how genetic variability accounts for differences between individuals in physiologic and metabolic capacity.

Studies were made of 15 pairs of identical twins (with the same heredity since they came from the same fertilized egg) and 15 pairs of fraternal twins (who do not differ from ordinary siblings because they result from separate fertilization of two eggs) raised in the same city by parents with similar socioeconomic backgrounds. The researchers concluded that heredity alone accounted for up to 93% of the observed differences in aerobic capacity as measured by the VO2max. In addition, genetic determination accounted for 81% of the capacity of the short-term glycolytic energy system and 86% of maximum heart rate. Subsequent investigations of larger groups of brothers, fraternal twins, and identical twins indicate a significant but much smaller effect of inherited factors on aerobic capacity and endurance performance.

Estimates of the genetic effect equal about 20–30% for VO2max, 50% for maximum heart rate, and 70% for physical working capacity. Similar muscle fiber composition occurs for identical twins, whereas wide variation in fiber type exists among fraternal twins and brothers. Future research may determine the upper limit of genetic determination, but currently available data show that inherited factors contribute significantly to both functional capacity and exercise performance. A large genotype-dependency also exists for the potential for improving maximal aerobic and anaerobic power, and the adaptations of most muscle enzymes to training. In other words, members of the same twin-pair generally show the same response to exercise training. Genetic makeup plays such a prominent role in determining training response that it is nearly impossible to predict a specific individual’s response to a given training stimulus.

Training StateVO2max scores must be evaluated relative to the person’s state of training at the time of

measurement. Improvements in aerobic capacity with training generally range between 6 and 20%, although increases have been reported as high as 50% above pretraining levels.

GenderVO2max values (mL•kg-1•min-1) for women typically average 15 to 30% below scores for men.

Even among trained athletes, this difference ranges between 15 and 20%. Such differences increase considerably when expressing the VO2max as an absolute value (L•min–1) rather than relative to body mass (mL•kg-1•min-1). Between world-class male and female cross-country skiers, for example, a 43% lower VO2max value for women (6.54 vs. 3.75 L•min–1) decreased to 15% (83.8 v 71.2 mL•kg-1•min-1) using the athletes' body mass in the ratio expression of VO2max.

Sex difference in VO2max has generally been attributed to differences in body composition and hemoglobin content. Untrained young adult women generally possess about 25% body fat, whereas the corresponding value for men averages 15%. Although trained athletes have a lower percentage of fat, trained women still possess significantly more body fat than male

Figure 6. General trend for maximal oxygen uptake with age and level of activity in males and females.


counterparts. Thus, the male generally generates more total aerobic energy simply because he possesses a relatively large muscle mass and less fat than the female.

Probably due to their higher level of testosterone, men show a 10 to 14% greater concentration of hemoglobin. This difference in the blood's oxygen-carrying capacity potentially enables males to circulate more oxygen during exercise and gives them a slight edge in aerobic capacity.

Although lower body fat and higher hemoglobin provide the male with some advantage in aerobic power, we must look for other factors to fully explain the disparity between the sexes. Differences in normal physical activity level between an “average” male and “average” female provide a possible explanation. Perhaps considerably less opportunities exist for women to become as physically active as men due to social structure and constraints. In fact, even among prepubertal children, boys become more active in daily life than their female counterparts.

AgeChanges in VO2max relate to chronological age. Although limitations exist in drawing

inferences form cross-sectional studies of different people at different ages, the available data provide insight into the possible effects of aging on physiologic function. Figure 6 shows the VO2max as a function of age. Note the dramatic increases during the growth years. Longitudinal studies (measuring the same people over a prolonged period) of children’s aerobic capacity show that absolute VO2max increases from about 1.0 L•min-1 at age 6 years to 3.2 L•min-1 at age 16 years. VO2max in girls peaks at about age 14 and declines thereafter. At age 14, the differences in VO2max between boys and girls approximate 25%, with the spread reaching 50% by age 16. Note also the decline in VO2max with increasing age. Beyond age 25, VO2max

declines steadily at about 1% per year, so that by age 55 it averages 27% below values reported for 20 year olds.

One’s habitual level of physical activity through middle age determines changes in aerobic capacity to a greater extent than chronological age.

Body CompositionDifferences in body mass explain roughly 70% of the differences in VO2max scores among

individuals. Thus, meaningful comparisons of exercise performance or the absolute value (L•min-1) for VO2max become difficult among individuals who differ in body size or body composition. This has led to the common practice of expressing oxygen uptake in terms of these components – either related to body surface area (BSA), body mass, fat-free body mass (FFM), or limb volume.



1. Anaerobic capacity

2. Anaerobic power

3. Average power

4. Glycogen depletion

5. Graded exercise test

6. Joule

7. Jumping power tests

8. Peak VO2max

9. Power

10.Relative VO2max

11.Stair sprinting power test

12.“True” VO2max


13.VO2max

14.VO2max Criteria

15.Watt

16.Wingate test

STUDY QUESTIONS

Overview of Energy Transfer Capacity During ExerciseIdentify the energy system that primarily supports each of the following activities:

Standing vertical jump and reach

Four hundred meter run

Three mile run

Power = ______________ x _______________ ÷ _______________.

Anaerobic Energy: The Immediate and Short-Term Energy SystemsEvaluation of the Immediate Energy SystemWhat type of tests typically measures the immediate anaerobic energy system?

Stair-Sprinting Power TestsCompute the power output for a person who weighs 55 kg and traverses nine steps in 0.75 seconds (vertical rise each step equals 0.175 meters).

Jumping-Power TestsGive one factor that might limit power jumping test scores as measures of the power output capacity of intramuscular high-energy phosphates.


Other Power TestsList two tests (other than stair-sprinting) to estimate power output capacity of the immediate energy system.

1.

2.

Evaluation of the Short-Term Energy SystemWhat type of test best estimates the power output capacity of the short-term energy system?

Performance Tests of Glycolytic PowerList two tests to measure short-term energy transfer capacity.

1.

2.

List three factors that affect anaerobic power performance.1. 3.

2.

Other Anaerobic TestsName one other exercise performance test to measure anaerobic power and capacity.

Glycogen DepletionList two factors that determine muscle glycogen depletion in different muscle fiber types within the same muscle.

1.

2.

Buffering of Acid MetabolitesDo athletes have an enhanced buffering capacity compared to non-athletes?


MotivationWhat relationship would you expect between “pain tolerance” and one’s capacity for anaerobic exercise? Explain.

Aerobic Energy: The Long-Term Energy SystemList three categories of athletes that typically exhibit high values for VO2max?

1. 3.

2.

Measurement of Maximal Oxygen Uptake

Criteria for VO2max

Describe the “gold standard” to indicate attainment of true VO2max.

Tests of Aerobic PowerList two general criteria for a good test of VO2max.

1.

2.

Factors That Affect Maximal Oxygen UptakeList six factors that influence VO2max.

1. 4.

2. 5.

3. 6.

Mode of ExerciseIndicate the most common piece of exercise equipment to determine VO2max.

HeredityWhat is the estimated magnitude of heredity in determining VO2max?


Training StateGive the general range for VO2max improvement with training?

SexGive one reasons for sex-related differences in VO2max.

AgeAfter age 30 y what happens to VO2max?

Body CompositionHow does body size influence VO2max?

What is the “best” way to express VO2max? Explain.

PRACTICE QUIZ1. Power Output:

a. F x D / Tb. D x T / Fc. work / timed. force x worke. none of the above

2. A Watt:a. measure of oxygen uptakeb. measure of glycolysisc. measure of powerd. measure of distancee. none of the above

3. Jumping tests measure:a. aerobic powerb. OBLA

c. EPOCd. localized energy depletione. none of the above

4. Trained athletes compared to untrained:

a. have greater buffering capacity

b. have lower buffering capacityc. have the same buffering

capacityd. have reduced buffering after

traininge. none of the above


5. Among the following athletes who has the highest VO2max:

a. fencersb. speed skatersc. swimmersd. cross-country skierse. weight lifters

6. Women compared to men:a. have lower VO2max

b. have higher VO2max

c. have about the same VO2max

d. higher buffering capacitiese. none of he above

7. Estimates of genetic effects on VO2max:

a. no effectb. 5%c. 20-30%d. 60%e. none of the above

8. VO2max decreases about ___% in aging:a. 1% per yearb. 10% per yearc. 15% per yeard. 25% per yeare. none of the above

9. Body composition can explain about ___of the differences in VO2max:

a. 10%b. 30%c. 50%d. 70%e. none of the above

10. Performance tests of anaerobic power would include:

a. long distance runsb. flexibility testsc. stair-sprinting power testd. walking testse. none of the above


LECTURE #8PHYSIOLOGIC SUPPORT SYSTEMS AND EXERCISE

IntroductionMost sport, recreational, and occupational activities require a moderately intense yet

sustained energy release. The aerobic breakdown of carbohydrates, fats, and proteins generates this energy for ADP phosphorylation to ATP. Without a steady rate between oxidative phosphorylation and the energy requirements of physical activity, an anaerobic-aerobic energy imbalance develops, lactic acid accumulates, tissue acidity increases, and fatigue quickly ensues. Two factors limit an individual’s ability to sustain a high level of exercise intensity without undue fatigue:

Capacity for oxygen delivery Capacity of specific muscle cells to generate ATP aerobicallyUnderstanding the role of the ventilatory, circulatory, muscular, and endocrine systems

during exercise enables us to appreciate the broad range of individual differences in exercise capacity. Knowing the energy requirements of exercise and the corresponding physiologic adjustments necessary to meet these requirements provides a sound basis to formulate an effective physical fitness program and evaluate one's physiologic and fitness status before and during such a program.

Figure 1. Overview of the ventilatory system showing the respiratory passages, alveoli, and gas exchange function in an alveolus.


Part 1. Pulmonary System and Exercise

Pulmonary Structure and FunctionIf oxygen supply depended only on diffusion through the skin, it would be impossible to

support the basal energy requirement, let alone the 3- to 5-liter oxygen uptake each minute to sustain a world class 5-minute per mile marathon pace. The remarkably effective ventilatory system meets the body’s needs for gas exchange.

The ventilatory system, depicted in Figure 1, regulates the gaseous state of our “external” environment for aerating fluids of the “internal” environment during rest and exercise. The major functions of the ventilatory system include:

Supply oxygen for metabolic needs Eliminate carbon dioxide produced in metabolism Regulate hydrogen ion concentration to maintain acid-base balance

Anatomy of VentilationThe "term pulmonary

ventilation" describes how ambient air moves into and exchanges with air in the lungs. About 1 foot (0.3 m) represents the distance between the ambient air just outside the nose and mouth and the blood flowing through the lungs. Air entering the nose and mouth flows into the conductive portion of the ventilatory system. Here it adjusts to body temperature, and becomes filtered and almost completely humidified as it moves through the trachea. The trachea is a short one-inch diameter tube that extends from the and divides into two tubes of smaller diameter called bronchi. The bronchi serve as primary conduits within the right and left lungs.

They further subdivide into numerous bronchioles that

conduct inspired air through a tortuous, narrow route until it eventually mixes with the air in the alveoli, the terminal branches of the respiratory tract.

LungsThe lungs provide the surface between blood and the external environment. Lung volume

varies between 4 and 6 liters (amount of air in a basketball) and provides an exceptionally

Figure 2. The lungs provide an exceptional surface for gas exchange.


large moist surface. For example, the lungs of an average-sized person weigh about 1 kg, yet if spread out as in Figure 2, they would cover a surface of 60 to 80 m2. This equals about 35 times the surface of the person, and would cover almost one-half a tennis court! This represents a considerable interface for aeration of blood because during any one second of maximal exercise, no more than 1 pint of blood flows in the lung tissue’s fine network of blood vessels.

AlveoliLung tissue contains more than 300 million alveoli each.

These elastic, thin-walled, membranous sacs provide the vital surface for gas exchange between the lungs and blood. Alveolar tissue has the largest blood supply of any organ in the body. In fact, the lung receives the entire output of blood from the heart (cardiac output). Millions of thin-walled capillaries and alveoli lie side by side, with air moving on one side and blood on the other. The capillaries form a dense mesh that covers almost the entire outside of each alveolus. This web becomes so dense that blood flows as a sheet over each alveolus. Once blood reaches the pulmonary capillaries, only a single cell barrier, the respiratory membrane, separates blood from air in the alveolus. This thin tissue-blood barrier permits rapid gas diffusion between the blood and alveolar air.

During rest, approximately 250 mL of oxygen leaves the alveoli each minute and enter the blood, and about 200 mL of carbon dioxide diffuse in the reverse direction into the alveoli. When trained endurance athletes perform heavy exercise, about 20 times the resting oxygen uptake transfers across the respiratory membrane. The primary function of pulmonary ventilation during rest and exercise is to maintain a fairly

constant, favorable concentration of oxygen and carbon dioxide in the alveolar chambers. This ensures effective gaseous exchange before the blood leaves the lungs for its transit throughout the body.

Mechanics of VentilationThe lungs do not merely suspend in the chest cavity. Rather, the difference in pressure

within the lungs and the lung-chest wall interface causes the lungs to adhere to the chest wall interior and literally follow its every movement. Any change in thoracic cavity volume thus produces a corresponding change in lung volume. Because lung tissue does not contain voluntary muscle, the lungs depend on accessory means to alter their volume. The action of voluntary skeletal muscle during inspiration and expiration alters thoracic dimensions, which brings about changes in lung volume.

InspirationThe diaphragm, a large, dome-shaped sheet of muscle makes an airtight separation between

the abdominal and thoracic cavities. During inspiration, the diaphragm muscle contracts, flattens out, and moves downward up to 10 cm toward the abdominal cavity. This enlarges the chest cavity and makes it more elongated. The air in the lungs then expands reducing its pressure (referred to as intrapulmonic pressure) to about 5 mm Hg below atmospheric pressure.

Inspiration concludes when thoracic cavity expansion ceases and intrapulmonic pressure increases to equal atmospheric pressure.

Figure. 3. Static measures of lung volume and capacity.


ExpirationExpiration, a predominantly a passive process, occurs as air moves out of the lungs. It

results from the recoil of stretched lung tissue and relaxation of the inspiratory muscles. This makes the sternum and ribs swing down, while the diaphragm moves back toward the thoracic cavity. These movements decrease the volume of the chest cavity, compressing alveolar gas and move it out through the respiratory tract into the atmosphere. During ventilation in moderate to heavy exercise, the internal intercostal muscles and abdominal muscles act powerfully on the ribs and abdominal cavity. This triggers a more rapid and greater depth of exhalation.

Respiratory muscle actions change thoracic dimensions to create a pressure differential between the inside and outside of the lung to drive airflow along the respiratory tract. Greater involvement of the pulmonary musculature (as occurs during progressively heavier exercise), causes larger pressure differences and concomitant increases in air movement.

Lung Volumes and CapacitiesFigure 3 depicts the various lung volume measures that reflect one’s ability to increase the

depth of breathing. The figure also shows average values for men and women while breathing from a calibrated recording spirometer that measures oxygen uptake by the closed-circuit method. Two types of measurements, static and dynamic, provide information about lung function dimensions and capacities. Static lung function measures evaluate the dimensional component for air movement within the pulmonary tract, and impose no time limitation on the subject. In contrast, dynamic lung functions evaluate the power component of pulmonary performance during different phases of the ventilatory excursion.

Static Lung VolumesDuring measurement of

static lung function the spirometer bell falls and rises with each inhalation and exhalation to provide a record of the ventilatory volume and breathing rate. Tidal volume (TV) describes air moved during either the inspiratory or expiratory phase of each breathing cycle. For healthy men and women, TV under resting conditions usually ranges between 0.4 and 1.0 liters of air per breath.

After recording several representative TVs, the subject breathes in normally and then inspires maximally. This additional volume of about 2.5 to 3.5 liters above the inspired tidal air represents the reserve for inhalation, termed the inspiratory reserve volume (IRV). The normal breathing pattern begins once again


following the IRV. After a normal exhalation, the subject continues to exhale and forces as much air as possible from the lungs. This additional volume, the expiratory reserve volume (ERV), ranges between 1.0 and 1.5 liters for an average-sized man (and 10 to 20% lower for a woman). During exercise, TV increases considerably because of encroachment on IRV and ERV, particularly the IRV.

Forced vital capacity (FVC) represents the total air volume moved in one breath from full inspiration to maximum expiration, or vice versa, with no time limitation. Although values for FVC can vary considerably with body size and body position during the measurement, average values usually equal 4 to 5 liters in healthy young men and 3 to 4 liters in healthy young women. FVCs of 6 to 7 liters are not uncommon for tall individuals, and values of 7.6 liters have been reported for a professional football player and 8.1 liters for an Olympic gold medalist in cross-country skiing. Large lung volumes of some athletes probably reflect genetic influences because static lung volumes do not change appreciably with exercise training.

Dynamic Lung VolumesDynamic measures of pulmonary ventilation depend on two factors: Volume of air moved per breath (tidal volume) Speed of air movement (ventilatory rate)Airflow speed depends on the pulmonary airways' resistance to the smooth flow of air and

resistance offered by the chest and lung tissue to changes in shape during breathing.

Forced Expiratory Volume-To-Forced Vital Capacity RatioNormal values for vital capacity can occur in severe lung disease if no limit exists on the

time to expel air. For this reason, a dynamic lung function measure such as the percentage of the FVC expelled in one second (FEV1.0) is more useful for diagnostic purposes. Forced expiratory volume-to-forced vital capacity ratio (FEV1.0/FVC) reflects expiratory power and overall resistance to air movement in the lungs. Normally, the FEV1.0/FVC averages about 85%. With severe pulmonary (obstructive) lung disease (e.g., emphysema and/or bronchial asthma), the FEV1.0/FVC becomes greatly reduced, often reaching less than 40% of vital capacity. The clinical demarcation for airway obstruction equals the point at which less than 70% of the FVC can be expelled in one second.

Maximum Voluntary VentilationAnother dynamic test of ventilatory capacity requires rapid, deep breathing for 15 seconds.

Extrapolation of this 15-second volume to the volume breathed had the subject continued for one minute represents the maximum voluntary ventilation (MVV). For healthy, college-aged men, the MVV usually ranges between 140 and 180 liters. The average for women equal 80 to 120 liters. Male members of the United States Nordic Ski Team averaged 192 liters per minute, with an individual high MVV of 239 liters per minute. Patients with obstructive lung disease achieve only about 40% of the MVV predicted normal for their age and body size. Specific pulmonary therapy benefits patients because training the breathing musculature increases the strength and endurance of the respiratory muscles (and enhances MVV).

Pulmonary Ventilation

Minute VentilationDuring quiet breathing at rest, an adults" breathing rate averages 12 breaths per minute

(about 1 breath every 5 s), whereas tidal volume averages about 0.5 liter of air per breath. Under these conditions, the volume of air breathed each minute (minute ventilation) equals 6 liters.


Minute ventilation (VE) = Breathing rate x Tidal volume6.0 L•min–1 = 12 x 0.5 L

An increase in depth or rate of breathing or both significantly increases minute ventilation. During maximal exercise, the breathing rate of healthy young adults usually increases to 35 to 45 breaths per minute, although elite athletes can achieve 60 to 70 breaths per minute. In addition, tidal volume commonly increases to 2.0 liters and larger during heavy exercise, causing exercise minute ventilation in adults to easily reach 100 liters or about 17 times the resting value. In well-trained male endurance athletes, ventilation may increase to 160 liters per minute during maximal exercise. In fact, several studies of elite endurance athletes report ventilation volumes of 200 liters per minute. Even with these large minute ventilations, the tidal volume rarely exceeds 55 to 65% of vital capacity.

Alveolar VentilationAlveolar ventilation refers to the portion of minute ventilation that mixes with the

air in the alveolar chambers. A portion of each breath inspired does not enter the alveoli, and thus does not engage in gaseous exchange with the blood. This air that fills the nose, mouth, trachea, and other nondiffusible conducting portions of the respiratory tract constitutes the anatomical dead space. In healthy people, this volume averages 150 to 200 mL, or about 30% of the resting tidal volume.

Because of dead-space volume, approximately 350 mL of the 500 mL of ambient air inspired in each tidal volume at rest mixes with existing alveolar air. This does not mean that only 350 mL of air enters and leaves the alveoli with each breathe. To the contrary, if tidal volume equals 500 mL, then 500 mL of air enters the alveoli but only 350 mL represents fresh air (or about one-seventh of the total air in the alveoli). Such a relatively small, seemingly inefficient alveolar ventilation prevents drastic changes in the composition of alveolar air; this ensures a consistency in arterial blood gases throughout the entire breathing cycle.

Table 1 shows that minute ventilation does not always reflect actual alveolar ventilation. In the first example of shallow breathing, tidal volume decreases to 150 mL, yet a 6-L minute ventilation results when breathing rate increases to 40 breaths per minute. The same 6-L minute volume results by decreasing breathing rate to 12 breaths per minute and increasing tidal volume to 500 mL. Doubling tidal volume and halving the ventilatory rate, as in the example of deep breathing, again produces a 6-L minute ventilation. Each ventilatory adjustment drastically affects alveolar ventilation. In the example of shallow breathing, dead-

space air represents the entire air volume moved (no alveolar ventilation has taken place.)

Depth Versus RateIncreases in the rate and depth of breathing maintain alveolar ventilation during increasing

exercise intensities. In moderate exercise, well-trained endurance athletes achieve adequate

Table 1. Relationship among tidal volume, breathing rate, and minute and alveolar minute ventilation.


alveolar ventilation by increasing tidal volume and only minimally increasing breathing rate.

With deeper breathing, alveolar ventilation can increase from 70% of the minute ventilation at rest to over 85% of the total exercise ventilation.

Ventilatory adjustments during exercise occur unconsciously; each individual develops a “style” of breathing by blending breathing rate and tidal volume so alveolar ventilation matches alveolar perfusion. Conscious attempts to modify breathing during general physical activities such as running usually fail and do not benefit exercise performance. In fact, conscious manipulation of breathing detracts from the exquisitely regulated ventilatory adjustments to exercise. At rest and exercise, each individual should breathe in the manner that seems most natural.

Gas ExchangeOur oxygen supply depends on the oxygen concentration in ambient air and its pressure.

Ambient (atmospheric) air composition remains relatively constant at 20.93% for oxygen, 79.04% for nitrogen (includes small quantities of inert gases that behave physiologically like nitrogen), 0.03% for carbon dioxide, and usually small quantities of water vapor. The gas molecules move at great speeds and exert a pressure against any surface they contact. At sea level, the pressure of air's gas molecules raises a column of mercury to an average height of

760 mm (29.9 in.). This barometric reading varies somewhat with changing weather conditions and decreases predictably at increased altitude.

Ambient AirTable 2. Percentages, partial pressures, and volumes of gases in 1 liter of dry ambient air at sea level.

Gas Percentage

Partial Pressure (at 760 mmHg)

Volume of Gas

(mL•L-1)Oxygen 20.93 159 209.3Carbon dioxide

0.03 0.02 0.4

Nitrogen 79.04 600 790.3Table 2 presents the volume, percentage, and partial pressures of gases in dry, ambient air

at sea level. The partial pressure of oxygen equals 20.93% of the total 760 mm Hg pressure exerted by air, or 159 mmHg (0.2093 x 760 mm Hg); the random movement of the minute quantity of carbon dioxide exerts a pressure of only 0.2 mm Hg (0.0003 x 760 mmHg), while nitrogen molecules exert a pressure that raises the mercury in a manometer about 600 mm

FOR YOUR INFORMATIONRESPIRED GASES: CONCENTRATION AND PARTIAL

PRESSURESGas concentration should not be confused with gas pressure.

Gas concentration reflects the amount of gas in a given volume – determined by the gas' partial pressure x solubility [Gas concentration = partial pressure x solubility]

Gas pressure represents the force exerted by the gas molecules against the surfaces they encounter.

Partial Pressure = Percent concentration x Total pressure of gas mixture


(0.7904 x 760 mmHg). The letter P before the gas symbol denotes partial pressure. For sea level ambient air: PO2 = 159 mmHg; PCO2 = 0.2 mmHg; PN2 = 600 mmHg.

Tracheal AirAir entering the nose and mouth passes down the respiratory tract; it becomes completely

saturated with water vapor, that slightly dilutes the inspired air mixture. At body temperature, for example, the pressure of water molecules in humidified air equals 47 mm Hg; this leaves 713 mmHg (760 - 47) as the total pressure exerted by the inspired dry air molecules at sea level. Consequently, the effective Po2 in tracheal air decreases by about 10 mmHg from its ambient value of 159 mm Hg to 149 mmHg (0.2093 x [760 - 47 mmHg]). Humidification has little effect on the inspired PCO2 because of carbon dioxide's almost negligible concentration in inspired air.

Alveolar AirAlveolar air composition differs considerably from the incoming breath of moist ambient air

because carbon dioxide continually enters the alveoli from the blood, whereas oxygen leaves the lungs for transport throughout the body. Table 3 shows that alveolar air contains approximately 14.5% oxygen, 5.5% carbon dioxide, and 80.0% nitrogen.

Table 3. Percentages, partial pressures, and volumes of gases in 1 liter of dry alveolar air at sea level.

Gas Percentage

Partial Pressure (at

760-47 mmHg)

Volume of Gas

(mL•L-1)

Oxygen 14.5 103 145Carbon dioxide

5.5 39 55

Nitrogen 80.0 571 800Water 47

After subtracting vapor pressure in moist alveolar gas, the average alveolar Po2 equals 103 mmHg (0.145 x [760 - 47 mmHg]) and 39 mmHg (0.055 x [760 - 47 mmHg]) for PCO2. These values represent the average pressures exerted by oxygen and carbon dioxide molecules against the alveolar side of the respiratory membrane. They do not exist as physiologic constants, but vary slightly with the phase of the ventilatory cycle and adequacy of ventilation in various lung segments.

Gas Exchange in the BodyThe exchange of gases between the lungs and blood, and their movement at the tissue level,

takes place entirely passively by diffusion.

Gas Exchange in LungsThe first step in oxygen transport involves oxygen transfer from oxygen alveoli into the

blood. The alveolar Po2 equals 100 mmHg, which is less than the Po2 of ambient air. Three main reasons for the dilution of oxygen in inspired air include:

Water vapor saturates relatively dry inspired air Oxygen is continually removed from alveolar air Carbon dioxide is continually added to alveolar airThe pressure of oxygen molecules in alveolar air averages about 60 mm Hg higher than the

Po2 in venous blood entering the pulmonary capillaries. Consequently, oxygen diffuses through the alveolar membrane into the blood. Carbon dioxide exists under slightly greater pressure in


returning venous blood than in the alveoli causing diffusion of carbon dioxide from the blood into the lungs. Although only a small pressure gradient of 6 mm Hg exists for carbon dioxide diffusion compared with oxygen, adequate carbon dioxide transfer occurs rapidly because of carbon dioxide's high solubility. Nitrogen, an inert gas in metabolism, remains essentially unchanged in alveolar-capillary gas.

Gas Exchange in the TissuesIn the tissues, where energy metabolism consumes oxygen at a rate almost equal to carbon

dioxide production, gas pressures can differ considerably from arterial blood. At rest, the average Po2 in the muscle's extracellular fluid rarely drops below 40 mmHg, while cellular PCO2 averages about 46 mmHg. In contrast, heavy exercise can reduce the pressure of oxygen molecules in muscle tissue to 3 mmHg, whereas the pressure of carbon dioxide approaches 90 mmHg. The pressure differential between gases in plasma and tissues establishes the gradients for diffusion – oxygen leaves capillary blood and diffuses toward metabolizing cells, while carbon dioxide flows from the cell to the blood. Blood then enters the veins and returns to the heart for delivery to the lungs. Diffusion rapidly begins once again as venous blood enters the lung's dense capillary network.

Oxygen and Carbon Dioxide Transport

Oxygen Transport in the BloodThe blood transports oxygen in two ways:1. In physical solution – dissolved in the fluid portion of the blood.2. Combined with hemoglobin – in loose combination with the iron-protein hemoglobin

molecule in the red blood cell

Oxygen Transport in Physical SolutionOxygen does not dissolve readily in fluids. At an alveolar Po2 of 100 mm Hg, only about 0.3

mL of gaseous oxygen dissolves in the plasma of each 100 mL of blood (3 mL of oxygen per liter of blood). Because the average adult’s total blood volume equals about 5 liters, 15 mL of oxygen dissolve for transport in the fluid portion of the blood (3 mL per L x 5 = 15 mL). This amount of oxygen could sustain life for only about four seconds. Viewed from a different perspective, the body would need to circulate 80 liters of blood each minute just to supply the resting oxygen requirements if oxygen were transported only in physical solution. This represents a blood flow two times higher than the maximum ever recorded for an exercising human!

Oxygen Combined With Hemoglobin (Hb)The blood of many animal species contains a metallic compound to augment its oxygen-

carrying capacity. In humans, the iron-containing protein pigment hemoglobin constitutes the main component of the body’s 25 trillion red blood cells. Hemoglobin increases the blood’s oxygen-carrying capacity 65 to 70 times above that normally dissolved in plasma. Thus, for each liter of blood, hemoglobin temporarily “captures” about 197 mL of oxygen. Each of the four iron atoms in a hemoglobin molecule loosely binds one molecule of oxygen to form oxyhemoglobin in the reversible oxygenation reaction:

Hb + 4 O2 ––––––––> Hb4O8

This reaction requires no enzymes. The partial pressure of oxygen in solution solely determines the oxygenation of hemoglobin to oxyhemoglobin.

Figure 4. Oxyhemoglobin dissociation curve under physiologic conditions at rest (arterial pH 7.4, tissue temperature 37°C). The right vertical axis shows the quantity of oxygen combined with Hb in each 100 mL of blood. The horizontal red line indicates Hb’s percent saturation at sea level alveolar PO2. The dashed line shows percent saturation at a PO2 of 40 mm Hg (tissue and venous blood).


Oxygen-Carrying Capacity of HemoglobinIn men, each 100 mL of blood contains approximately 15 to 16 g of hemoglobin. The value

averages 5 to 10% less for women, or about 14 g per 100 mL of blood. Sex difference in hemoglobin concentration contributes to the lower aerobic capacity of women, even after adjusting for differences in body mass and fat.

Each gram of hemoglobin can combine loosely with 1.34 mL of oxygen. Thus, oxygen-carrying capacity can be calculated by knowing blood’s hemoglobin concentration as follows:

Blood’s oxygen capacity = Hb (g•100 mL-1 blood) x Oxygen capacity of Hb (1.34 mL)

For example, if the blood’s hemoglobin concentration equals 15, then approximately 20 mL of oxygen (15 g per 100 mL x 1.34 mL = 20.1) would be carried with the hemoglobin in each 100 mL of blood if hemoglobin achieved full oxygen saturation (i.e., if all Hb existed as Hb408).

Po2 and Hemoglobin SaturationThus far, the discussion of

blood’s oxygen-carrying capacity assumes that hemoglobin achieves full saturation with oxygen when exposed to alveolar gas.

Figure 4 shows the relationship between percent hemoglobin saturation (left vertical axis) at various Po2s under normal resting physiologic conditions (arterial pH 7.4, 37°C) and the effects of changes in pH (Figure 6B) and temperature (Figure 6C) on hemoglobin’s affinity for oxygen. Percent saturation of hemoglobin computes as follows:Percent saturation = (Total

O2 combined with Hb (Oxygen carrying capacity

of Hb) x 100This curve, termed the

"oxyhemoglobin dissociation curve", quantifies the amount of

oxygen carried in each 100 mL of normal blood in relation to plasma Po2 (right axis). For example, at a Po2 of 90 mm Hg the normal complement of hemoglobin in 100 mL of blood is about 19 mL of oxygen; at 40 mm Hg the oxygen quantity falls to 15 mL, and 6.5 mL at a Po2 of 20 mm Hg.

The Bohr EffectFigures 5B and 5C show that increases in acidity (H+ concentration and CO2) or

temperature cause the oxyhemoglobin dissociation curve to shift downward to the right (to enhance unloading of oxygen), particularly in the Po2 range of 20 to 50 mm Hg. This

Figure 6B, Oxyhemoglobin dissociation curve. Effects of changes in pH ([H+]) on hemoglobin’s affinity for oxygen. 6C, Effects of changes in temperature on hemoglobin’s affinity.


phenomenon, known as the Bohr effect (named after its discoverer physiologist Christian Bohr), results from alterations in hemoglobin’s molecular structure.

Bohr Effect becomes important in vigorous exercise, as increased metabolic heat and acidity in tissues augments oxygen release. For example, at a Po2 of 20 mm Hg and normal body temperature (37°C), %O2 saturation of hemoglobin equals 35%. At the same Po2, with body temperature increased to 43°C (like at the end of a marathon run), hemoglobin’s saturation decreases to about 23%. Thus, more oxygen unloads from hemoglobin for use in cellular metabolism. Similar effects take place with increased acidity.


Part 2. Circulation System and Exercise

IntroductionThe Greek physician Galen (Lecture 2) theorized about blood flow in the body. He believed

blood flowed like the tides of the sea, surging and abating into arteries, then away from the heart and back again. In Galen’s view, fluid carried with it “humors”, good and evil that determined one’s well-being. If a person became ill, the standard practice required bloodletting to drain off the diseased humors and restore health. This theory prevailed until the seventeenth century when physician William Harvey (Lecture 2) proposed a different scenario. Experimenting with frogs, cats, and dogs, Harvey demonstrated the existence of valves in the heart that provided for one-way movement of fluid, a finding incompatible with Galen’s “ebb-and-flow” view because it suggested a circular flow of blood through the body. In a set of ingenious experiments, Harvey measured the volume of the heart chambers and counted the number of times the heart contracted in one hour. He concluded that if the heart emptied only one-half its volume with each beat, the body’s total blood volume would be pumped in minutes. These finding led Harvey to hypothesize that blood moved (circulated) within a closed system in a circular pattern throughout the body. Harvey, of course, was correct; we now know that the heart pumps the entire blood volume, approximately five liters, in one minute. Harvey’s experiments changed medical science forever, although it would take nearly two hundred more years for his ideas to play important roles in physiology and medicine.

From Harvey’s early experiments of the sophisticated research at the dawn of the twenty first century, we now know that the highly efficient ventilatory system complements a rapid transport and delivery system comprised of blood, the heart, and more than 60,000 miles of blood vessels that integrate the body as a unit. The circulatory system serves five important functions during physical activity:

1. Delivers oxygen to active tissues2. Aerates blood returned to the lungs3. Transports heat, a by-product of cellular metabolism, from the body's core to the skin4. Delivers fuel nutrients to active tissues5. Transports hormones, the body’s chemical messengers

Components of the Cardiovascular SystemThe cardiovascular system consists of an interconnected, continuous vascular circuit

containing a pump (heart), a high-pressure distribution system (arteries), exchange vessels (capillaries), and a low-pressure collection and return system (veins). Figure 6 presents a schematic view of this system.


HeartThe heart provides the force to propel blood throughout the vascular circuit. This four-

chambered organ, a fist-sized pump, beats at rest an average of 70 times a minute, 100,800 times a day, and 36.8 million times a year. Even for a person of average fitness, maximum output of blood from this remarkable organ exceeds fluid output from a household faucet turned wide open!

Functionally, the heart consists of two separate pumps: one pump (left heart pump) receives blood from the body and pumps it to the lungs for aeration (pulmonary circulation and the

Figure 6. Schematic view of the cardiovascular system consisting of the heart and the pulmonary and systemic vascular circuits.


other pump (right heart pump) accept oxygenated blood from the lungs and pump it throughout the body (systemic circulation).

The hollow chambers of the heart’s right side (right heart) perform two important functions:1. Receive blood returning from all parts of the body 2. Pump blood to the lungs via the pulmonary circulation for aeration

The left side of the heart (left heart) also performs two important functions:1. Receive oxygenated blood from the lungs2. Pump blood into the thick-walled, muscular aorta for distribution throughout the

body in the systemic circulation A thick, solid muscular wall (septum) separates the left and right sides of the heart. The

atrioventricular (AV) valves situated within the heart direct the one-way flow of blood from the right atrium to the right ventricle (tricuspid valve) and from the left atrium to the left ventricle (mitral or bicuspid valve). The semilunar valves located in the arterial wall just outside the heart prevent blood from flowing back into the heart between ventricular contractions.

The relatively thin-walled, sac-like atrial chambers serve as primer pumps to receive and store blood returning from the lungs and body during ventricular contraction. About 70% of the blood that returns to the atria flows directly into the ventricles before the atria contract. Simultaneous contraction of both atria forces remaining blood into their respective ventricles directly below. Almost immediately after atrial contraction, the ventricles contract and force blood into their specific arterial systems.

ArteriesThe arteries provide the high-pressure tubing that conducts oxygen-rich blood to tissues.

Arteries are composed of layers of connective tissue and smooth muscle. Because of their thickness, no gaseous exchange takes place between arterial blood and surrounding tissues. Blood pumped from the left ventricle into the highly muscular yet elastic aorta circulates throughout the body via arterioles, or smaller arterial branches. Arteriole walls contain circular layers of smooth muscle that either constrict or relax to regulate peripheral blood flow. This redistribution function becomes particularly important during exercise because blood diverts to working muscles from areas that temporarily compromise their blood supply.

CapillariesThe arterioles continue to branch and form smaller and less muscular vessels called

metarterioles. These tiny vessels end in capillaries, a network of microscopic blood vessels so thin they provide only enough room for blood cells to squeeze through in single file. Capillaries generally contain about 5% of the total blood volume at any time. Gases, nutrients, and waste products rapidly transfer across the thin, porous, capillary walls. A ring of smooth muscle (precapillary sphincter) encircles the capillary at its origin to control the vessel’s internal diameter. This sphincter provides a local means for regulating capillary blood flow within a specific tissue in response to metabolic requirements that change rapidly and dramatically in exercise.

VeinsThe vascular system maintains continuity of blood flow as capillaries feed deoxygenated

blood at almost a trickle into small veins called venules. Blood flow then increases slightly because the venous system cross-sectional area is less than for capillaries. The lower body’s smaller veins eventually empty into the largest vein, the inferior vena cava, that travels through the abdominal and chest cavities toward the heart. Venous blood draining the head, neck, and shoulder regions empties into the superior vena cava and moves downward to join


the inferior vena cava at heart level. The mixture of blood from the upper and lower body then enters the right atrium and descends into the right ventricle for delivery through the pulmonary artery to the lungs. Gas exchange takes place in the lungs’ alveolar-capillary network; here, the pulmonary veins return oxygenated blood to the left heart, where the journey through the body resumes.

VENOUS RETURN

A unique characteristic of veins solves a potential problem related to the low pressure of venous blood. Because of low venous blood pressure, muscular contractions or minor pressure changes within the chest cavity during breathing compress the veins. Alternate venous compression and relaxation, combined with the one-way action of valves, provides a “milking” effect similar to the action of the heart. Venous compression imparts considerable energy for blood flow, whereas “diastole” (relaxation) allows vessels to refill as blood moves toward the heart. Without valves, blood would stagnate or pool (as it sometimes does) in veins of the extremities, and people would faint every time they stood up because of reduced blood flow to the brain.

A SIGNIFICANT BLOOD RESERVOIR

The veins do not merely function as passive conduits. At rest, the venous system normally contains about 65% of the total blood volume; hence, the veins serve as capacitance vessels, or blood reservoirs. A slight increase in tension (tone) by the vein’s smooth muscle layer alters the diameter of the venous tree. A generalized increase in venous tone rapidly redistributes blood from peripheral veins toward the central blood volume returning to the heart. In this manner, the venous system plays an important role as an active blood reservoir to either retard or enhance blood flow to the systemic circulation.

VARICOSE VEINS

Sometimes valves within a vein become defective and fail to maintain one-way blood flow. This condition of varicose veins usually occurs in superficial veins of the lower extremities from the force of gravity that retards blood flow in an upright posture. As blood accumulates, these veins become excessively distended and painful, often impairing circulation from surrounding areas. In severe cases, the venous wall becomes inflamed and degenerates – a condition called phlebitis, which often requires surgical removal of the vessel. Individuals with varicose veins should avoid excessive straining exercises like heavy resistance training.

Venous PoolingThe fact that people faint when forced to maintain an upright posture without movement

(e.g., standing at attention for a prolonged period) demonstrates the importance of muscle contractions to venous return. Also, changing from a lying to a standing position affects the dynamics of venous return and triggers physiologic responses. Heart rate and blood pressure stabilize during bed rest. If a person suddenly rises and remains erect, an uninterrupted column of blood exists from heart level to the toes, creating a hydrostatic force of 80 to 100 mm Hg. Swelling (edema) occurs from pooling of blood in the lower extremities and creates “back pressure” that forces fluid from the capillary bed into surrounding tissues. Concurrently, impaired venous return decreases blood pressure; at the same time, heart rate accelerates, and venous tone increases to counter the hypotensive condition. Maintaining an upright position without movement leads to dizziness and eventual fainting from insufficient cerebral blood supply. Resuming a horizontal or head-down position restores circulation and consciousness.

The Active Cool-DownThe existence of venous pooling justifies continued slow jogging or walking after strenuous

exercise. A “cooling down” with rhythmic exercise facilitates blood flow through the vascular

Figure. 7. Pulse rate taken at (A) temporal, (B) carotid, and (C) radial arteries.


circuit (including the heart) during recovery. An “active recovery” also aids in lactic acid removal from the blood. The pressurized suits worn by test pilots and special support stockings also aid in retarding hydrostatic shifts of blood to veins of the lower extremities in the upright position. A similar supportive effect occurs in upright exercise in a swimming pool because the water’s external support facilitates venous return.

Blood PressureA surge of blood enters the

aorta with each contraction of the left ventricle, distending the vessel and creating pressure within it. The stretch and subsequent recoil of the aortic wall propagates as a wave through the entire arterial system. The pressure wave appears in the following areas: as a pulse in the superficial radial artery on the thumb side of the wrist, in the temporal artery (on the side of the head at the temple), and/or at the carotid artery along the side of the trachea (Figure 7).

In healthy persons, pulse rate equals heart rate. The highest pressure generated by left ventricular contraction (systole) to move blood through a healthy, resilient vascular system at rest usually reaches 120 mm Hg. As the heart relaxes (diastole) and aortic valves close, the natural elastic recoil of the aorta and other arteries provide a continuous head of pressure to

move blood to the periphery until the next surge from ventricular systole. During the cardiac cycle’s diastole, arterial blood pressure decreases to 70-80 mm Hg. Arteries “hardened” by mineral and fatty deposits within their walls, or with excessive peripheral resistance to blood flow from kidney malfunction or nervous strain, induce systolic pressures as high as 300 mm Hg and diastolic pressures above 120 mmHg.

RestResting High blood pressure (resting-hypertension) imposes a chronic strain on normal

cardiovascular function. If left untreated, severe hypertension leads to heart failure; the heart muscle weakens, unable to maintain its normal pumping ability. Degenerating, brittle vessels can obstruct blood flow, or can burst, cutting off vital blood flow to brain tissue causing a stroke.

Blood pressure classificationSystolic (mmHg) Diastolic (mmHg) Category

<130 <85 Normal130-139 85-89 High normal140-159 90-99 (Stage 1) hypertension

160-179 100-109 Moderate (Stage 2) hypertension

180-209 110-119 Severe (Stage 3) hypertension

>210 120 Very severe (Stage 4) hypertension


During Rhythmic ExerciseDuring rhythmic muscular activities like brisk walking, hiking, jogging, swimming, and

bicycling, dilation of the active muscles’ blood vessels increases the vascular area for blood flow. The alternate, rhythmic contraction and relaxation of skeletal muscles provides significant force to propel blood through the vessels and return it to the heart. Increased blood flow during moderate exercise causes systolic pressure to rapidly rise in the first few minutes and level off, usually between 140 and 160 mm Hg; diastolic pressure remains relatively unchanged.

During Resistance ExerciseStraining-type exercises (e.g., heavy resistance exercise, shoveling wet snow) produce

acute, dramatic blood pressure increases because sustained muscular force compresses peripheral arterioles, significantly increasing resistance to blood flow. The heart’s additional workload from acute elevations in blood pressure increases risk for individuals with existing hypertension or coronary heart disease. In such cases, rhythmic forms of moderate physical activity provide health benefits..

BODY INVERSION

Inversion devices that allow a person to hang upside-down have been used for years to increase relaxation, facilitate a strength-training response, and relieve lower back pain. However, no one has yet demonstrated with careful research that inverting the body provides any practical medical or physiologic benefits. On the negative side, the maneuver can trigger a significant rise in blood pressure at the start and throughout the inversion period. This raises concern about possible consequences of inversion for people with hypertension, and the wisdom of performing exercises in the upside-down position. A brief period of inversion also doubles pressure within the eye in healthy adults. Clearly, individuals with eye disorders should refrain from inversion.

IN RECOVERY

Following a bout of sustained light- to moderate-intensity exercise, systolic blood pressure temporarily decreases below pre-exercise levels for up to 12 hrs in normal and hypertensive subjects. Pooling of blood in the visceral organs and lower limbs during recovery reduces central blood volume, which contributes to a lower blood pressure. The hypotensive recovery

FOR YOUR INFORMATIONDETERMINANTS OF BLOOD PRESSUREArterial blood pressure reflects arterial blood flow per minute (cardiac output) and peripheral vascular resistance to that flow in the following relationships:

Total peripheral resistance (TPR) = Blood Pressure (BP) ÷ Cardiac Output (CO)

Blood Pressure = Cardiac Output x Total Peripheral Resistance

FOR YOUR INFORMATIONBLOOD PRESSURE AND RACEAfrican Americans have twice the incidence of high blood pressure as Caucasians and nearly seven times the rate of severe hypertension. The fact that African Americans in the United States have a much greater incidence of hypertension than blacks in Africa compounds the issue of race and hypertension. Researchers now focus on the possible causative role of diet, stress, cigarette smoking, and other lifestyle and environmental factors that trigger this chronic blood pressure response in genetically susceptible blacks.


response further supports the use of exercise as important nonpharmacologic hypertension therapy. A potentially effective approach spreads several bouts of moderate physical activity throughout the day.

Cardiovascular Dynamics During Exercise

Cardiac OutputCardiac output provides the primary indicator of the circulatory system’s functional

capacity to meet the demands of physical activity. As with any pump, the rate of pumping (heart rate) and quantity of blood ejected with each stroke (stroke volume) determine the heart’s output:

Cardiac output (CO) = Heart rate (HR) x Stroke volume (SV)

Resting Cardiac OutputUNTRAINED PERSONS

Each minute, the left ventricle ejects the entire 5-liter (5000 mL) blood volume of an average-sized adult male. This value remains similar for most individuals, but stroke volume and heart rate vary considerably depending on cardiovascular fitness status. A heart rate of about 70 beats per minute generally sustains the average adult’s 5-liter resting cardiac output. Substituting this heart rate value in the cardiac output equation (cardiac output = stroke volume x heart rate; stroke volume = cardiac output ÷ heart rate), yields a calculated stroke volume of 71 mL per beat.

ENDURANCE ATHLETES

Resting heart rate for an endurance athlete generally averages about 50 beats per minute. Because the athlete’s resting cardiac output also averages 5 liters per minute, blood circulates with a proportionately larger stroke volume of 100 mL per beat (5000 mL ÷ 50). Stroke volumes for women usually average 25% below values for men of equivalent training status. The smaller body size of the average woman chiefly accounts for this “sex difference.”

The underlying mechanisms for the heart rate and stroke volume differences between trained and untrained individuals remain unclear. Two factors probably interact as aerobic fitness improves:

1. Increased vagal tone slows the heart allowing more time for ventricular filling2. Enlarged ventricular volume and a more powerful myocardium combine to eject a larger

volume of blood with each systole

FOR YOUR INFORMATIONCardiac Output In Trained And Untrained Subjects at Rest and During Maximal Exercise

Cardiac Output = Heart rate x Stroke Volume

Untrained Rest 5000 mL = 70 b•min-1 x 71 mL•b-1

Maximal Ex. 22,000 mL = 195 b•min-1 x 113 mL•b-1

Endurance Trained Rest 5000 mL = 50 b•min-1 x 100 mL•b-1

Maximal Ex. 35,000 mL = 195 b•min-1 x 179 mL•b-1

Figure 8. Heart rate in relation to oxygen uptake during upright exercise in endurance athletes. The triangles are for athletes and the circles are for sedentary college students.

Sedentary

Trained


Exercise Cardiac OutputBlood flow from the heart increases in direct proportion to exercise intensity. From rest to

steady-rate exercise, cardiac output increases rapidly, followed by a more gradual increase until it plateaus so blood flow matches exercise metabolic requirements.

In sedentary, college-aged men, cardiac output in strenuous exercise increases about four times resting to an average maximum of 22 L per minute. HRmax for these young adults averages about 195 bpm. Thus, stroke volume averages 113 mL of blood per beat during maximal exercise (22,000 mL/195). In contrast, world-class endurance athletes generate max cardiac outputs of 35 L•min-1, with similar or slightly lower HRmax than the untrained. Thus, difference between maximum cardiac output relates to differences in stroke volume.

Exercise Stroke VolumeStroke volume increases linearly to about 50%

VO2max and then levels off until termination of exercise. For some subjects, stroke volume decreases slightly at higher exercise intensities. Physiologists agree that stroke volume and oxygen uptake increase linearly to about 50% VO2max.

Heart Rate During ExerciseGraded Exercise

Figure 8 shows the relationship between heart rate and oxygen uptake during exercise of increasing intensity to maximum for endurance athletes (triangles) and sedentary college students (circles). Similar lines relate heart rate and oxygen uptake for both groups throughout the major portion of the exercise range. Heart rate for the untrained person accelerates rapidly with increasing oxygen uptake; a much smaller heart rate increase occurs for athlete. Consequently, trained persons achieve a higher level

of exercise oxygen uptake at a particular submaximal heart rate than a sedentary person.


Submaximum ExerciseHeart rate increases rapidly and levels off within several minutes during submaximum

steady-rate exercise. A subsequent increase in exercise intensity causes heart rate to rise to a new plateau as the body attempts to match the cardiovascular response to metabolic demands. Each increment in exercise intensity requires progressively more time to achieve heart rate stabilization.

Cardiac Output DistributionBlood flow to specific tissues generally increases in proportion to their metabolic activity.

RestFigure 9 (A) shows the approximate distribution of a 5-liter cardiac output at rest. More

than one-fourth of the cardiac output flows to the liver; one-fifth to muscle tissue; and the brain, kidneys, and digestive tract also require relatively large amounts of blood.

During ExerciseFigure 9 (B) illustrates the distribution to various tissues during intense aerobic exercise.

Although regional blood flow varies considerably depending on environmental conditions, level of fatigue, and the mode of exercise, active muscles receive a disproportionately large portion of the cardiac output. Each 100 g of muscle receives 4 to 7 mL of blood per minute during rest. Muscle blood flow increases steadily during exercise to reach a maximum of between 50-75 mL per 100 g of tissue.

Figure 9. Relative distribution of cardiac output during rest (A) and strenuous endurance exercise (B). Numbers in parenthesis = percent of total cardiac output. Despite its large mass, muscle receives about the same amount of blood as the much smaller kidneys at rest. In strenuous exercise, however, 85% of cardiac output diverts to active muscle.


LECTURE #8 STUDY GUIDE

Define Key Terms and Concepts1. Alveolar ventilation

2. Alveoli

3. Ambient air

4. Anatomical dead space

5. Arteriovenous oxygen difference

6. Bohr effect

7. Dyspnea

8. Emphysema

9. FEV1.0 / FVC

10.Forced vital capacity

11.Hemoglobin

12.Hyperventilation


13.Minute ventilation

14.Oxyhemoglobin

15.Oxyhemoglobin dissociation curve

16.Partial pressure of gas

17.Percent saturation

18.Po2

19.Pulmonary ventilation

20.Ventilatory system

21.Arteries

22.Bradycardia

23.Cardiac output

24.Diastolic blood pressure

25.ECG


26.Hypertension

27.Stroke volume

28.Systole

29.Veins

STUDY QUESTIONS

Pulmonary Structure and FunctionList three functions of the ventilatory system.

1. 3.

2.

Anatomy of VentilationPlace the following terms in the order of airflow movement during the inspiratory cycle: bronchioles, trachea, alveoli, and bronchi.

1. 3.

2. 4.

LungsGive the surface area dimension of the lungs?

AlveoliWhat is the primary function of the alveoli?

Mechanics of VentilationWhat causes the changes in lung volume during inspiration and expiration?


InspirationList three muscles involved in inspiration.

1. 3.

2.

ExpirationList three factors that cause expiration of air from lungs.

1. 2.

3.

Static Lung VolumesName three static lung volumes

1.

2.

3.

Dynamic Lung VolumesWhat two factors determine dynamic lung volumes?

1.

2.

Forced Expiratory Volume-to-Forced Vital Capacity Ratio.Forced expiratory volume provides an indication of what two components of lung function?

1.

2.

Maximum Voluntary Ventilation


Discuss whether or not the MVV exceeds the ventilation volume observed during maximal exercise.

Pulmonary VentilationMinute VentilationMinute Ventilation = ___________________ x ____________________

Alveolar VentilationWhat is the best way to increase alveolar minute ventilation, increasing depth or rate of breathing?

Depth Versus RateDiscuss the contributions of breathing rate and tidal volume to the increased ventilation during heavy exercise.

Gas ExchangeAmbient AirCompute the partial pressures of O2, CO2, and N2 of ambient air at sea level (barometric pressure = 760 mm Hg).

Po2 = ___________________ x ___________________

Pco2 = __________________ x ___________________

Pn2 = ___________________ x ___________________

Alveolar AirGive the average percent of O2, CO2 and N2 in alveolar air at sea level.

O2 =

CO2 =

N2 =

Gas Exchange in the Body


What is the average partial pressure of O2 and CO2 in the alveoli at rest? How does heavy exercise affect these values?

O2 CO2

RestHeavy Exercise

Gas Exchange In the LungsList three reasons that account for the dilution of oxygen in inspired air compared to ambient air.

1. 3.

2.

Gas Exchange in the TissuesGive the average partial pressures of O2 and CO2 in tissues at rest. How does heavy exercise affect these values?

Oxygen and Carbon Dioxide TransportOxygen Transport in the BloodList two ways for oxygen to transport in the blood.

1.

2.

Oxygen Transport in Physical SolutionFor every 100 mL of blood how much oxygen is dissolved?

Oxygen Combined With Hemoglobin (Hb)Write the formula for the oxygenation of hemoglobin to oxyhemoglobin:

Oxygen-Carrying Capacity of HemoglobinList the average hemoglobin values (g per 100 mL blood) for men and women.

Men


Women

Each gram of hemoglobin loosely combines with _______ mL of oxygen.

Po2 and Hemoglobin SaturationGive the formula for calculating percent saturation of hemoglobin.

The Bohr EffectList three factors that cause the oxyhemoglobin dissociation curve shift downward and to the right to facilitate oxygen release.

1. 3.

2.

Components of the Cardiovascular SystemList four important functions of the circulatory system.

1. 3.

2. 4.

HeartWhat type of muscle makes up the myocardium?

ArteriesWhat is the main function of the arteries and arterioles?

CapillariesHow long does it take a blood cell to pass through a typical capillary?

VeinsVenous ReturnWhat do veins have that arteries do not have?

A Significant Blood Reservoir


About how blood do the veins contain during rest?

Venous PoolingDescribe venous pooling.

The Active Cool-DownWhy is it always beneficial to actively cool down after exercise compared to lying down in recovery?

Blood PressureRestIdentify three good places on the body to feel the pulse wave as blood passes through the arterial system?

1. 3.

2.

During Rhythmic ExerciseGive a typical blood pressure during rhythmic muscular exercise.

During Resistance ExerciseWhy shouldn't hypertensive individuals engage in heavy resistance training?

Body InversionDiscuss whether or not hypertensive individuals should perform body inversion exercises.

In RecoveryWhy is aerobic exercise sometimes recommended as a therapy modality for hypertensive individuals?

Cardiovascular Dynamics During Exercise


Cardiac OutputWrite the equation for cardiac output.

Resting Cardiac OutputUntrained PersonsList a typical cardiac output for an untrained man and women?

Man

Women

Endurance AthletesList a typical cardiac output for an endurance trained man and women?

Man

Women

Exercise Cardiac OutputGive a typical maximum cardiac output for a sedentary person.

Heart Rate During ExerciseCalculate your maximum heart rate.

Cardiac Output DistributionIn the following table show the relative distribution (%) of the cardiac output during rest and exercise to the skeletal muscles, digestive tract, liver, and kidneys.

Rest Exercise

Muscles

Digestive tract

Liver

Kidneys


PRACTICE QUIZ1. There are about ______ alveoli per

lung:a. 100 millionb. 300 millionc. 800 milliond. 1 billione. none of the above

2. Inspiration:a. passive procedureb. active procedurec. does not require energyd. initiates with heart beate. none of the above

3. Tidal volume:a. volume in lungs after tidal

expirationb. volume in lungs after inspirationc. volume inspired or expired per

breadthd. same as residual volumee. none of the above

4. FVC:a. maximum volume expired after

maximum inspirationb. volume in lungs after tidal

expirationc. same as residual volumed. decreases due to traininge. none of the above

5. Partial pressure:a. gas concentration x solubility

b. gas concentration x % in airc. gas pressure x volumed. %concentration x total pressuree. none of he above

6. Oxygen combined with hemoglobin:a. Hb4O8

b. HbCO2

c. only in venous bloodd. 1.34 mLe. none of he above

7. Bohr effect:a. effects of temperature and

pressure on HbO2 curveb. effects of oxygen on Hb

saturationc. effects of Hb on oxygen curved. occurs in venous blood onlye. none of the above

8. Blood pressure =:a. cardiac output x total peripheral

resistanceb. cardiac output x stroke volumec. stroke volume x blood pressured. heart rate x stroke volumee. none of the above

9. True or false: In healthy people, pulse rate equals heart rate:a. Tb. F

10. A normal resting cardiac output:a. 5000 mLb. 10000 mLc. 200 mLd. 195 beats per minutee. none of the above

Figure 1. Classification of physical activity on the basis of duration of all-out exercise and the corresponding predominant intracellular energy pathway.


LECTURE #9TRAINING THE ENERGY SYSTEMS

IntroductionFigure 1 illustrates exercise classified in terms of duration and predominant energy

pathways. It is difficult to place certain activities into only one category. For example, as a person increases aerobic fitness, an activity previously classified as anaerobic may reclassify as aerobic. In many cases, all three energy-transfer systems operate at different times. Their contributions to the energy continuum directly relate to the duration and intensity (power output) of the specific activity.

Brief power activities lasting up to 6-sec rely exclusively on “immediate” energy generated from breakdown of stored intramuscular high-energy phosphates, ATP and PCr. As all-out exercise progresses to 1 min duration and power output decreases, the major portion of energy still generates through anaerobic pathways. These metabolic reactions involve the short-term energy system of glycolysis with subsequent lactate accumulation. As exercise intensity diminishes and duration extends to 2-4 minutes aerobic ATP production becomes more important. Prolonged

exercise progresses on a “pay-as-you-go” basis, with aerobic metabolism generating 99% of the energy requirement. The basic approach to physiologic conditioning applies similarly to men and women within a broad age range: both respond similarly.

Objectives Discuss and provide examples of exercise training principles of overload, specificity,

individual differences, and reversibility. Outline metabolic adaptations from anaerobic exercise training. Describe influences of (1) initial fitness level, (2) genetics, (3) training frequency, (4)

training duration, and (5) training intensity on the response to aerobic training.


Discuss the rationale for using heart rate to establish exercise intensity for aerobic training.

Discuss the term “training-sensitive zone.” Describe the most common cause of the overtraining syndrome.


Physiological Training PrinciplesStimulating functional adaptations that improve performance in specific tasks represents

the major objective of exercise training. These adaptations require adherence to carefully planned programs, with attention focused on factors such as frequency and length of workouts, type of training, speed, intensity, duration, and repetition of the activity, rest intervals, and appropriate competition. Application of these factors varies depending on the performance and fitness goals. However, several principles of physiologic conditioning remain common to improving performance in the diverse physical activity classifications illustrated in Figure 1.

Overload PrincipleThe regular application of a specific exercise overload enhances physiologic function to

bring about a training response. Exercising at intensities higher than normal induces a variety of highly specific adaptations that enable the body to function more efficiently. Achieving the appropriate overload for each person requires manipulating combinations of training frequency, intensity, and duration, with specific attention paid to exercise mode.

The concept of individualized and progressive overload applies to athletes, sedentary people, the disabled, and even cardiac patients. An increasing number in this latter group have applied appropriate exercise rehabilitation to walk, jog, and eventually run marathons! Achieving significant health-related benefits of regular exercise (e.g., metabolic parameters, lipid profile, blood pressure) requires a focus on accumulation of total exercise and a considerably lower exercise intensity than necessary to improve cardiovascular fitness.

Specificity PrincipleExercise training specificity refers to adaptations in metabolic and physiologic functions

that depend upon the type of overload imposed. The acronym “SAID” – specific adaptations to imposed demands, describes this principle. A specific anaerobic exercise stress (e.g., strength-power training) induces specific strength-power adaptations, while specific endurance exercise stress elicits specific aerobic system adaptations — with only a limited interchange of benefits derived between strength-power and aerobic training. However, the specificity principle extends beyond this broad demarcation. For example, “aerobic training” does not represent a singular entity requiring only cardiovascular overload. Aerobic training utilizing the specific muscles in the desired performance most effectively improves aerobic fitness for activities like swimming, bicycling, running, or upper-body exercise. Some evidence even suggests a temporal specificity in training response such that indicators of training improvement reach there highest when measurements take place at the time of day training regularly occurred.

Furthermore, the most effective evaluation of sport-specific performance results when the laboratory measurement most closely simulates the actual sport activity and/or activates the muscle mass required by the sport. Simply stated, specific exercise elicits specific adaptations creating specific training effects (SAID).

Individual Differences PrincipleMany factors contribute to individual variation in the training response. For example, a

person’s relative fitness level at the start of training exerts an influence. Even for a relatively homogenous group who starts exercise training together, one cannot expect different people who start exercise training together all individuals to reach the same “state” of fitness (or performance) after 10 or 12 weeks. Consequently, a coach should not insist that all athletes on the same team (or even in the same event) train the same way or at the same relative or absolute exercise intensity. It also is unrealistic to expect all individuals to respond to a given training stimulus in precisely the same manner.


Reversibility PrincipleLoss of physiologic and performance adaptations (detraining) occurs rapidly when a person

terminates participation in regular exercise. Only 1 or 2 weeks of detraining significantly reduces both metabolic and exercise capacity, with many training improvements totally lost within 8 weeks. One research group provides particularly interesting findings. In five subjects confined to bed for 20 consecutive days, VO2max decreased by 25% (1% per day). This decrease accompanied a similar decrement in maximal stroke volume and cardiac output. Additionally, the number of capillaries within trained muscle decreases between 14 and 25% within 3 weeks after training ceased. For elderly subjects, 4 months of detraining results in the complete loss of adaptations in the cardiovascular system.

Even among highly trained athletes, the beneficial effects of many years of prior exercise training remain transient and reversible. For this reason, most athletes begin a reconditioning program several months prior to the start of the competitive season, or maintain some moderate level of off-season, sport-specific exercise to blunt the decline in physiologic functions during deconditioning.

Physiologic Consequences of TrainingThe following section present a listing of the diverse adaptations in response to anaerobic

and aerobic exercise training outlined in Table 1.Table 1. Typical Metabolic and Physiologic Values for Health, Trained and Untrained Men.

Variable Untrained

Trained

Percent Diff

Glycogen, mM# mitochondria, mMolMitochondrial volume,%muscle Resting ATP, mMResting creatine, mMAerobic Enzymes, SDHMax stroke volume mL/bResting HR, b/minMax Cardiac output, L/minMax Heart rate, b/minMax a-v O2diff, mL/dLVO2max, mL/kg/min

85.00.592.153.010.75-101207020

19014.5

30-40

1201.208.06.0

14.515-2018040

30-4018016.0

65-80

4110327210035

13350-4375-510

107

Anaerobic System Changes With TrainingConsistent with the concept of training specificity, activities that demand a high level of

anaerobic metabolism bring about specific changes in the immediate and short-term energy systems, without a concomitant increase in aerobic functions. The changes that occur with sprint-power training include:

Increased levels of anaerobic substrates. As determined from muscle biopsies taken before and after resistance training, significant increases in the trained muscle’s resting levels of ATP, PCr, free creatine, and glycogen accompanied a 28% improvement in muscular strength.

Increased quantity and activity of key enzymes that control anaerobic-phase glucose catabolism. These changes do not reach the magnitude observed for oxidative enzymes with aerobic training. The most dramatic increases in anaerobic enzyme function and fiber size occur in the fast-twitch muscle fibers.


Increased capacity to generate high levels of blood lactate during all-out exercise. An enhanced lactate-producing capacity probably results from: (1) increased levels of glycogen and glycolytic enzymes, and (2) improved motivation and “pain” tolerance to fatiguing exercise.

Aerobic System Changes With TrainingTable 2 illustrates that aerobic overload training induces significant adaptations in a variety

of functional capacities related to oxygen transport and utilization. With an adequate training stimulus, the majority of these responses occur independent of gender and age. Many of the training-induced aerobic adaptations also occur in coronary heart disease patients undergoing high-intensity aerobic training.

Aerobic Metabolic AdaptationsAerobic training significantly improves the capacity for respiratory control in skeletal

muscle.

Metabolic MachineryThe primary effect of endurance training produces an increase in muscle mitochondrial

capacity. The results of many different experiments indicate that mitochondria do not increase in specific activity per se, rather, trained skeletal muscle contains larger and more numerous mitochondria but its activity remains the same as less active muscle fibers. The exact training stimuli (intensity, time, recovery, etc.) resulting in more mitochondria remains a central focus of current research.

Fat MetabolismEndurance training increases an individual’s capacity to mobilize, deliver, and oxidize fatty

acids for energy during submaximal exercise. Enhanced fat catabolism with aerobic training becomes particularly apparent at the same absolute submaximal exercise workload whether under fed or fasted conditions. Impressive increases also occur in the trained muscle’s capacity to utilize intramuscular triglycerides as the primary source for fatty acid oxidation. A more lively, training-induced lipolysis (fat use) results from:

Table 2. Physiologic factors that affect aerobic conditioning.

Ventilation-Aeration

Active Muscle Metabolism

Central Blood Flow

Peripheral Blood Flow

Minute ventilation Ventilation:perfusi

on ratio Oxygen diffusion

capacity Hb-O2 affinity Arterial oxygen

saturation

Enzymes and oxidative potential

Energy stores and substrate availability

Myoglobin concentration

Mitochondria size and number

Active muscle mass

Muscle fiber type

Cardiac output (heart rate, stroke volume)

Arterial blood pressure

Oxygen transport capacity

Flow to nonactive regions

Arterial vascular reactivity

Muscle blood flow

Muscle capillary density

Muscle vascular conductance

Oxygen extraction

Venous compliance and reactivity


Greater blood flow within trained muscle Enhanced quantity of fat-mobilizing and fat-metabolizing enzymes Enhanced muscle mitochondrial respiratory capacity (see above) Blunted catecholamine release for the same absolute power output after training

Carbohydrate MetabolismReduced total carbohydrate utilization in submaximal exercise with endurance training

results from the combined effects of (1) decreased muscle glycogen utilization, and (2) reduced production (decreased hepatic glycogenolysis and gluconeogenesis) and utilization of plasma-borne glucose. Fatty acid oxidation combined with a reduced level of carbohydrate metabolism contributes to blood glucose homeostasis and improved endurance capacity following aerobic training. Training-enhanced hepatic gluconeogenic capacity further provides resistance to hypoglycemia during prolonged exercise.

Muscle Fiber Type and SizeAerobic training elicits metabolic adaptations in each type of muscle fiber. The basic fiber

type probably does not “change” to any great extent, but, rather, all fibers maximize their already-existing aerobic potential.

Selective hypertrophy occurs in the different muscle fiber types in response to specific overload training. Highly trained endurance athletes have larger slow-twitch fibers than fast-twitch fibers in the same muscle. Conversely, the fast-twitch fibers of athletes trained in anaerobic-power activities occupy a much greater portion of the muscle’s cross-sectional area.

Cardiovascular AdaptationsTable 3 summarizes the most important adaptations in cardiovascular function with aerobic

exercise training that increase the delivery of oxygen to active muscle. Because of the intimate linkage of the cardiovascular and pulmonary systems to aerobic processes, endurance training produces significant dimensional and functional cardiovascular adaptations.

Table 3. Adaptations in cardiovascular function with aerobic exercise training that increases oxygen delivery to active muscles.• Increase plasma volume • Increase ejection fraction• Increase red blood cell mass • Increase maximum stroke volume• Increase total blood volume • Increase maximum cardiac output• Increase ventricular compliance • Optimize peripheral blood flow• Increase internal ventricular dimensions• Increase blood flow to active muscle• Increase venous return • Increase end diastolic volume• Increase myocardial contractility • Increase effectiveness of cardiac output • Decrease heart rate (12-15 b/min) distribution

The most important of the above changes resulting from training include: Decreased exercise heart rate at a given load Increased resting stroke volume resulting from enhanced left ventricular function Increased exercise stroke volume including maximum stroke volume Increased maximum cardiac output Increased maximum oxygen extraction Enhanced blood flow redistribution Increased blood flow to the heart


Decreased blood pressure

Factors That Affect the Aerobic Training ResponseFour factors significantly influence the aerobic training response:

1. Initial level of aerobic fitness 3. Training frequency2. Training intensity 4. Training duration

Initial Level of Aerobic FitnessThe magnitude of the training response depends upon one’s initial fitness level. Someone

who rates low at the start has considerable room for improvement. If capacity already rates high, the magnitude of improvement usually remains relatively small. Studies of sedentary, middle-aged men with heart disease showed that VO2max improved by 50%, while similar training in normally active, healthy adults elicited a 10 to 15% improvement. Of course, a 5% improvement in aerobic capacity represents as crucial a change for elite athlete as a 40% increase for the sedentary person. As a general guideline, aerobic fitness improvements generally range between 5 to 25% with systematic programs of endurance training. A portion of this improvement occurs within the first week of training.102

Training IntensityTraining-induced physiologic adaptations depend primarily on the intensity of overload.

There are at least seven different expressions of exercise intensity:1. As energy expended per unit time (e.g., 9 kcal•min-1 or 37.8 kJ•min-1).2. As absolute exercise level or power output (e.g., cycle at 900kg-m•min-1 or 147 W).3. As relative metabolic level expressed as percentage of VO2max (e.g., 85% VO2max).4. As exercise below, at, or above the lactate threshold (e.g., 4 mmol lactate).5. As exercise heart rate or percentage of maximum heart rate (e.g., 180 b•min-1 or 80%

HRmax).6. As multiples of resting metabolic rate (e.g., 6 METs).7. As rating of perceived exertion (e.g., RPE = 14).An example of absolute training intensity involves having all individuals exercise at the

same power output or energy expenditure (e.g., 9.0 kcal•min-1) over a 30-minute exercise session. When everyone exercises at the same exercise intensity, however, the task may pose a considerable stress for one person yet fall short of the training threshold for another more fit person. For this reason, the relative stress on a person’s physiologic systems is usually used. Consequently, the assigned exercise intensity usually relates to some break point for steady-rate exercise (e.g., lactate threshold, OBLA) or some percentage of maximum physiologic capacity (e.g., VO2max, HRmax, or maximum exercise capacity. The general practice establishes


PSYCHOLOGICAL BENEFITSSignificant potential benefits on psychological state emerge from regular exercise (either aerobic or resistance training), regardless of age. Adaptations include a reduction in state anxiety and blood pressure, decreased level of mild to moderate depression, reduction in neuroticism, and improved mood, self-esteem, self-concept, and general perception of personal worth, often to an extent equal to that achieved with other therapeutic interventions including pharmacologic therapy.

Figure 2. Maximum heart rates and the training sensitivity zone for use in aerobic training of men and women of different ages.


aerobic training intensity via direct measurement (or estimation) of VO2max (or HRmax), followed by assigning an exercise level that corresponds to some percentage of these maximums.

Although establishing training intensity from measures of oxygen consumption provides a high degree of accuracy, its use requires sophisticated equipment and thus becomes impractical for the general population. An effective alternative uses heart rate to classify exercise for relative intensity when establishing the training protocol. Use of exercise heart rate becomes possible because %VO2max and %HRmax relate in a predictable way regardless of gender, fitness level, or age. <tbl21.7>Table 21.7 presents selected values for %VO2max and corresponding %HRmax obtained from several sources. The error in estimating %VO2max from %HRmax, or vice versa, equals about ±8%. Thus, one need only monitor heart rate to estimate the relative exercise stress or %VO2max, within the given error range. The relationship between %HRmax and %VO2max remains essentially the same for arm or leg exercises among healthy subjects, normal weight and obese groups, cardiac patients, and people with spinal cord injuries. Importantly, however, arm (upper-body) exercise produces significantly lower HRmax compared to leg exercises.

Train at a Percentage of HRmax

As a general rule, aerobic capacity improves if exercise intensity regularly increases heart rate to at least 55 to 70% of maximum. During lower-body exercise like cycling, walking, or running, this heart rate increase equals about 45 to 55% of the VO2max, or, for college-aged men and women a heart rate of 120 to 140 b•min-1.

An alternative and equally effective method for establishing the training threshold, termed the Karvonen method has subjects exercise at a heart rate equal to 60% of the difference between resting and maximum. With the Karvonon method heart rate computes as follows:

HRthreshold = HRrest + 0.60 (HRmax – HRrest)This approach to determining heart rate training threshold gives a somewhat higher value

compared to computing the threshold heart rate simply as 70% HRmax.Clearly, positive training adaptations do not require strenuous levels of exercise. An

exercise heart rate of 70% maximum represents “moderate” exercise with little or no discomfort for most healthy people. This training level, frequently referred to as “conversational exercise,” reaches sufficient intensity to stimulate a training effect, yet does not produce a level of discomfort that limits a person from talking during the workout. This conversational exercise level indicates a lack of heavy breathing associated with lactic acidosis induced hyperpnea, a level of exercise where individuals can no longer talk and exercise comfortably. A previously sedentary person need not exercise above this heart rate to improve physiologic capacity.

The “Training-Sensitive Zone”

One can determine maximum exercise heart rate immediately after several minutes of all-out effort in a specific form of exercise. This exercise intensity requires considerable motivation and stress—a requirement certainly

Figure 3. Borg perceived exertion scale.


inadvisable for adults without medical clearance, particularly individuals predisposed to coronary heart disease. Consequently, people should consider themselves “average” and use the age-predicted maximum heart rates presented in Figure 2.

Although individuals of a specific age possess varying HRmax values, the inaccuracy resulting from individual variation (±10 b•min-1 standard deviation for any age-predicted HRmax) has little influence in establishing effective training for healthy people. Maximum heart rate computes as 220 minus the person’s age in years, with values independent of race or gender in children and adults.

HRmax + 220 – age, yAlthough this formula represents a convenient “rule of thumb,” it does not determine a

specific person’s maximum heart rate. Within normal variation, the maximum heart rate of 95% (±2 standard deviations) of 40-year-old men and women ranges between 160 and 200 b•min-1. Figure 2 also depicts the “training-sensitive zone” in relation to age. Conditioning the aerobic systems occurs as long as exercise heart rate remains within this zone.

A 40-year-old woman or man desiring to train at moderate intensity but still achieve the threshold level would select a training heart rate equal to 70% of age-predicted HRmax, or a target exercise heart rate of 126 b•min-1 (0.70 x 180). Then, using progressive increments of light to moderate exercise, the person achieves a walking, jogging, or cycling intensity that produces this heart rate. To increase training to 85% of maximum, exercise intensity must increase to produce a heart rate of 153 b•min-1 (0.85 x 180).

Is Strenuous Training More Effective?Generally, the higher the training intensity above threshold, the greater the training

improvement, particularly for VO2max. Although there exists a minimal “threshold” intensity below which a training effect does not occur, there may also exist a “ceiling” above which no further gains accrue. More fit men and women generally require higher threshold levels to stimulate a training response than less fit counterparts. The ceiling for training intensity remains unknown, although 85% VO2max (corresponding to 90% HRmax) probably represents an upper limit. Importantly, however, regardless of the exercise level selected, more does not necessarily produce greater results. Excessive intensity of physical training and abrupt increases in training volume increase the risk for injury to bones, joints, and muscles.

Is Less Intense Training Effective?The often cited recommendation of 70% HRmax

as a training threshold for aerobic improvement represents a general guideline for effective, yet comfortable exercise. The actual lower limit may depend on the participant’s initial exercise capacity and current state of training. In addition, older and less fit, and sedentary, overweight men and women show training thresholds closer to 60% HRmax, which corresponds to about 45% VO2max. Twenty to 30 minutes of continuous exercise at the 70% HRmax level stimulates a training effect; exercise at the lower intensity of 60% for 45 minutes also proves beneficial. Generally, a longer exercise duration offsets a lower exercise intensity.

Train at a Perception of EffortIn addition to oxygen consumption, heart rate,

and blood lactate as indicators of exercise

Figure 4. Absolute and percentage improvement in VO2max.


intensity, one also can use the rating of perceived exertion (RPE). Using this psycho-physiological approach, the exerciser rates on a numerical scale (Borg scale, after the researcher who developed this system) perceived feelings in relation to the exertion level.

Monitoring and adjusting RPE during exercise represents a relatively easy and effective means for prescribing exercise based on an individual’s perception of effort that coincides nicely with objective measures of physiologic/metabolic strain (%HRmax, %V02max, blood lactate concentration). Exercise levels corresponding to higher levels of energy expenditure and physiologic strain produce higher RPE ratings. For example, an RPE of 13 or 14 (exercise that feels “somewhat hard;” Figure 4) coincides with about 70% HRmax during cycle ergometer and treadmill exercise; an RPE between 11 and 12 corresponds to exercise at the lactate threshold for trained and untrained individuals. The RPE establishes an exercise prescription for exercise intensities corresponding to blood lactate concentrations of 2.5 mM (RPE - 15) and 4.0 mM (RPE - 18) during a 30 min treadmill run where subjects self regulated exercise intensity. Individuals learn quickly to exercise at a specific RPE.

Training DurationA threshold duration per workout has not been identified for optimal aerobic improvement.

This threshold probably depends on the interaction of many factors including total work accomplished (duration or training volume), exercise intensity, training frequency, and initial fitness level. Whereas 3- to 5 minute daily exercise periods produce training effects in some poorly conditioned people, 20- to 30-minute exercise sessions achieve more optimal results (within practicality for time) if intensity reaches at least 70% HRmax. With higher-intensity training, significant improvements occur with only a 10-minute workout. Conversely, it requires at least 60 minutes of continuous exercise to produce a training effect when exercise intensity falls below 70% HRmax.

As for training volume, more does not necessarily produce greater results. In a study of collegiate swimmers, for example, one group trained for 1.5 hours daily while another group performed two 1.5-hour exercise sessions each day. Despite one group exercising at twice the daily exercise volume, no differences in swimming power, endurance, or performance time improvements emerged between groups.

Training FrequencyDoes 2 or 5 day-a-week training produce differing effects if exercise duration and intensity

remain constant for each training session? Unfortunately, the precise answer remains elusive. Some investigators report that training frequency significantly influences cardiovascular improvements while others maintain that this factor contributes considerably less than either exercises intensity or duration. Studies using interval training showed that training 2 days per week produced VO2max changes similar in magnitude to those when training 5 days per week. In other studies that held total exercise volume constant, no differences emerged in VO2max improvements between training frequencies of 2 versus 4, or 3 versus 5

days per week. As in the case with training duration, more frequent training becomes beneficial when

training at a lower intensity.


While the extra time invested to increase training frequency may not prove profitable for improving physiologic function, the extra quantity of exercise (e.g., 3- vs. 6-day per week training) often represents a considerable caloric expenditure. To affect meaningful weight loss through exercise, each exercise session should last at least 60 minutes at a sufficient intensity to expend 300 kcal or more. Training only one day per week generally does not produce meaningful changes in anaerobic or aerobic capacity, body composition, or weight loss.

Typical aerobic exercise training programs take place 3 days per week with a rest day usually spaced between workout days. One could reasonably question whether training on consecutive days would produce equally effective results? In an experiment concerned with this exact question, nearly identical improvements in VO2max occurred regardless of sequencing of the 3-day-per-week training schedule. This finding suggests that the stimulus for aerobic training links closely to exercise intensity and total work accomplished and not to the sequencing of training days.

Exercise ModeHolding exercise intensity, duration, and frequency constant produces a similar training

response, regardless of training mode—as long as the exercise involves relatively large muscle groups. Bicycling, walking, running, rowing, swimming, in-line skating, rope skipping, bench stepping, stair climbing, and simulated arm-leg climbing all provide excellent overload for the aerobic system. Of course, based on the specificity concept, the magnitude of training improvement varies considerably depending on the mode of testing. Individuals trained on a bicycle show greater improvements when tested on the bicycle than on the treadmill.195 Likewise, individuals who train by swimming or arm cranking show the greatest improvements when measured during upper-body exercise.

How Long Before Improvements Occur?The answer to the above question depends on the specific biologic systems affected by

training. Aerobic fitness adaptations occur rapidly, with significant improvements noted within several weeks.

Figure 4 shows improvements in VO2max for subjects who trained 6 days per week for 10 weeks. Training consisted of stationary cycling for 30 minutes 3 days per week combined with running for up to 40 minutes alternate days. The continuous week-to-week change in aerobic capacity indicates that training improvements in previously sedentary people occur rapidly and progress in relatively steady fashion. Of course, adaptive responses to training eventually level off as subjects approach their “genetically predisposed” maximums. The exact time for this leveling off remains unknown, particularly for those undergoing high-intensity training.

Trainability and GenesWhile a vigorous exercise-training program enhances a person’s level of fitness regardless

of genetic background, the limits for developing fitness capacity link closely to genetic endowment. For two individuals undertaking the same exercise program, one person might show 10 times more improvement than the other. Research in genetics indicates a genotype dependency for much of our sensitivity in responding to maximal aerobic and anaerobic power training, including the adaptations of most muscle enzymes. In other words, both members of an identical twins pair generally show a similar magnitude in training response. If one twin showed high responsiveness to training, a high likelihood existed that the other twin would also behave as a responder; similarly, the brother of a nonresponder to exercise training generally showed little improvement. Presence of the muscle-specific creatine kinase gene provides one example of the possible contribution of genetic makeup to individual differences in the responsiveness of VO2max to endurance training. Genetic makeup plays such a predominant role in training responsiveness that it is almost impossible to predict a specific individual’s response to a given training stimulus.


Maintenance of Aerobic Fitness GainsAn important question concerns the optimal frequency, duration, and intensity of exercise

required to maintain aerobic improvements with training. In one study, healthy young adults increased VO2max 25% with 10 weeks of interval training by bicycling and running 40 minutes, 6 days a week. They then joined one of two groups that continued to exercise an additional 15 weeks at the same intensity and duration but at a reduced frequency of either 4 or 2 days a week. Both groups maintained their gains in aerobic capacity despite as much as a two-thirds reduction in training frequency.

A similar study evaluated the effect of reduced training duration on the maintenance of improved aerobic fitness. Upon completion of the same protocol outlined above for the initial 10 weeks of training, the subjects continued to maintain intensity and frequency of training for an additional 15 weeks, but reduced training duration from the original 40-minute sessions to either 26- or 13-minutes per day. They maintained almost all VO2max and performance increases despite a two-thirds reduction in training duration. However, if intensity of training decreased and frequency and duration remained constant, even a one-third-exercise intensity reduction caused a significant decline in VO2max.

It appears that aerobic capacity improvement involves somewhat different training requirements than its maintenance. With intensity held constant, the frequency and duration of exercise required to maintain a certain level of aerobic fitness remains considerably less than that required for its improvement. A small drop off in exercise intensity, on the other hand, reduces VO2max. This indicates that exercise intensity plays a principal role in maintaining the increase in aerobic power achieved through training.

Fitness components other than VO2max more readily suffer adverse effects of reduced exercise training volume. Well-trained endurance athletes who normally trained 6 to 10 hours a week reduced weekly training to one 35-minute session showed no decrease in VO2max over a 4-week period. However, their endurance capacity at 75% VO2max significantly decreased, which related to reduced pre-exercise glycogen stores and a diminished level of fat oxidation during exercise. Such findings indicate that single measure like VO2max cannot adequately evaluate all factors that affect training and detraining adaptations.

Methods of TrainingEach year, performance improvements occur in almost all athletic competitions. These

advances generally relate to increased opportunities for participation: individuals with “natural endowment” more likely become exposed to particular sports. Also, improved nutrition and health care, better equipment, and more systematic and scientific approaches to athletic training contribute to superior performance.

In the following sections I present general guidelines for anaerobic and aerobic training, with particular emphasis on three general training classifications: (1) interval training, (2) continuous training, and (3) fartlek training.

Anaerobic TrainingFigure 1 demonstrated that the capacity to perform all-out exercise for up to 60 seconds

duration largely depends on ATP generated by the immediate and short-term anaerobic energy systems.

The Intramuscular High-Energy PhosphatesSports such as football, weightlifting, and other brief, sprint-power activities rely almost

exclusively on energy derived from ATP and PCr that comprise the muscles’ high-energy phosphates. Engaging specific muscles in repeated maximum bursts of effort for 5- to 10-second duration overloads this phosphagen pool. Because the intramuscular high-energy phosphates supply energy for brief, intense exercise, only small amounts of lactate accumulate

Figure 5. The two major goals of aerobic training: Goal #1 – develop the capacity of the central circulation to deliver oxygen; Goal #2 – Enhance the capacity of the active musculature to supply and process oxygen.


and recovery progresses rapidly (alactic recovery oxygen consumption). Thus, exercise can begin again after about a 30-second rest period. The use of brief, all-out exercise interspersed with recovery represents a specific application of interval training to anaerobic conditioning.

The activities selected in training to enhance ATP-PCr energy transfer capacity must engage the specific muscles at the movement speed and power output for which the athlete desires improved anaerobic power. Not only does this enhance the metabolic capacity of the specifically trained muscle fibers, but it also facilitates recruitment and modulation of firing sequence of the appropriate motor units activated in the actual movement.

Lactate–Generating CapacityAs duration of all-out effort extends beyond 10-seconds duration, dependence on anaerobic

energy from the intramuscular high-energy phosphates decreases with a proportionate increase in the magnitude of anaerobic energy from glycolysis. To improve energy transfer capacity by the short-term lactic acid energy system, training must overload this aspect of energy metabolism.

Anaerobic training requires extreme physiological and psychological demands and considerable motivation. Repeated bouts of up to 1-minute maximum exercise stopped 30 seconds before subjective feelings of exhaustion cause blood lactate to increase to near-maximum levels. The individual repeats each exercise bout after 3 to 5 minutes of recovery. Repetition of exercise causes a “lactate stacking,” which results in a higher blood lactate level than achieved with just one bout of all-out effort to exhaustion. Of course, as with all training, one must exercise the specific muscle groups that require enhanced anaerobic capacity. A backstroke swimmer trains by swimming the backstroke, a cyclist should bicycle, and basketball, hockey, or soccer players rapidly perform various movements and direction changes similar to those required by the demands of their sport.

Recovery requires considerable time when exercise involves a significant anaerobic component. For this reason, anaerobic power training should occur at the end of the conditioning session. Otherwise, fatigue might carry over and perhaps hinder one’s ability to perform subsequent aerobic training.

Aerobic TrainingFigure 5 indicates two

important factors in formulating an aerobic training program: Training must provide a sufficient cardiovascular overload to stimulate increases in stroke volume and cardiac output. The central circulatory overload must result from exercising the sport-specific muscle groups to enhance their local circulation and “metabolic machinery.” In essence, proper endurance training overloads all components of oxygen transport and utilization.

This consideration embodies the specificity principle as applied to aerobic training. Simply stated, runners should run, cyclists should bicycle, rowers should row, and swimmers should swim.


Relatively brief bouts of repeated exercise (interval training), as well as continuous, long-duration efforts (continuous training), enhance aerobic capacity, provided exercise reaches sufficient intensity to overload the aerobic system. Interval training, continuous training, and fartlek training represent three common methods to improve aerobic fitness.

Interval TrainingWith correct spacing of exercise and rest, one can perform extraordinary amounts of high-

intensity exercise, normally not possible if the exercise progressed continuously. The repeated exercise bouts (with rest periods or relief intervals) vary from a few seconds to several minutes or longer depending on the desired training outcome. The interval training prescription evolves from the following considerations:

Intensity of exercise interval Duration of exercise interval Length of recovery interval Number of repetitions of the exercise-recovery cycleConsider the following example of the ability to perform a considerable volume of high-

intensity exercise during an interval-training workout. Few people can maintain a 4-minute-mile pace for longer than 1 minute, let alone complete a mile within 4 minutes. Suppose we limited running intervals to only 10 seconds, followed by 30 seconds of recovery. This scenario makes it reasonably easy to maintain these exercise-rest intervals and complete the mile in 4 minutes of actual running. Although this does not parallel a world-class performance, the example does indicates that a person can accomplish a significant quantity of normally exhausting exercise given proper spacing of rest and exercise intervals.

Rationale for Interval TrainingInterval training has a sound basis in physiology and energy metabolism. In the example of

a continuous run at a 4-minute-mile pace, a large portion of energy derives from anaerobic glycolysis. Within a minute or two, the lactate level rises precipitously and the runner fatigues. During interval training, on the other hand, repeated 10-second exercise bouts permit completion of intense exercise without appreciable lactate buildup because the intramuscular high-energy phosphates provide the primary exercise energy source. Minimal fatigue results during the predominantly “alactic” exercise interval and recovery progresses rapidly. The exercise interval can then begin after only a brief rest.

The two factors are used in formulating an interval training programs include Exercise interval Relief interval

Continuous TrainingContinuous or long slow distance (LSD) training involves steady-paced, prolonged

exercise at either moderate or high aerobic intensity, usually between 60 to 80% VO2max. The exact pace can vary, but it must at least meet a threshold intensity to ensure aerobic physiologic adaptations. Continuous training for an hour or longer has become popular among joggers and other fitness enthusiasts including competitive endurance athletes such as triathletes and cross-country skiers. For example, some elite distance runners train twice a day and run between 100 and 150 miles each week while preparing for competition. In one report, a man training for the 52.5 mile ultramarathon ran twice daily, 20 miles in the morning and 13 miles in the evening; he interspersed these runs with occasional 30- to 60-mile non-stop runs at a 7- to 8-minute per mile pace. Within this schedule, he ran more than 800 miles each month and totaled 9600 miles for the year! The precise benefits of such considerable training remain unknown.


Because of its submaximum nature, continuous exercise training progresses for a considerable time in relative comfort. This contrasts with the potential hazards of high-intensity interval training for coronary-prone individuals and the high level of motivation required for such strenuous exercise. Continuous training ideally suits those beginning an exercise program or wishing to accumulate a large caloric expenditure for weight loss. When applied in athletic training, continuous training actually represents “over-distance” training, with most athletes training two to five times the actual distances of competitive events.

An advantage of continuous training for endurance athletes permits exercising at nearly the same intensity as actual competition. Because specific motor unit recruitment depends on exercise intensity, continuous training may best apply to endurance athlete in terms of adaptations at the cellular level. This contrasts to interval training that often places disproportionate stress on the fast-twitch motor units, not the slow-twitch units predominantly recruited in endurance competition.

Fartlek TrainingFartlek, a Swedish word means “speed play,” represents a training method introduced to

the United States in the 1940s. This relatively “unscientific” blending of interval and continuous training has particular application to exercise out-of-doors over natural terrain. The system utilizes alternate running at fast and slow speeds over both a level and hilly course.

In contrast to the precise exercise interval training prescription, fartlek training does not require systematic manipulation of the exercise and relief intervals. Instead, the performer determines the training schema based on “how it feels” at the time, in a way similar to gauging exercise intensity based on one’s rating of perceived exertion. If used properly, this method can overload one or all of the energy systems. Although lacking the systematic and quantified approaches of interval and continuous training, fartlek training provides an ideal means for general conditioning and off-season training. It also maintains a certain “freedom” and variety in workouts.

Insufficient evidence prevents proclaiming superiority of any specific training method for improving aerobic capacity. Each form of training produces success. One can probably use the various methods interchangeably, particularly to modify training and achieve a more psychologically pleasing exercise program.

Overtraining: Too Much of a Good ThingWith significant increases in heavy and prolonged exercise training over the past 15 years,

particularly in high-volume endurance sports, as many as 10 to 20% of athletes experience the syndrome of overtraining or “staleness.” As a result of a complex interaction of biological and psychological influences, the athlete fails to endure and adapt to training, normal exercise performance deteriorates, and the individual encounters increasing difficulty fully recovering from a workout. This takes on crucial importance for elite athletes where performance decrements of from 1 to 3% might cause a gold medallist to fail to qualify for competition.

Two clinical forms of overtraining have been described:1. The less common sympathetic form, characterized by increased sympathetic activity

during rest. Generally typified by hyper-excitability, restlessness, and impaired exercise performance. This form of overtraining may reflect the result of excessive psychological/ emotional stress that accompanies the interaction among training, competition, and responsibilities of normal living.

2. The more common parasympathetic form, characterized by predominance of vagal activity during rest and exercise. More properly termed “overreaching” in the early stages (within as few as 10 days), the syndrome is qualitatively similar in symptoms to the full-blown parasympathetic overtraining syndrome but of shorter duration. Overreaching generally results from excessive and protracted overload with inadequate recovery and


rest. Initially, maintenance of exercise performance requires greater effort, which eventually leads to performance deterioration in training and competition. Short-term rest intervention of a few days up to several weeks usually brings about full recovery. Untreated overreaching eventually leads to the overtraining syndrome.

Parasympathetic overtraining syndrome represents more than just short-term inability to train as hard as usual or a slight dip in competition-level performance. Rather, it involves chronic fatigue experienced during exercise workouts and subsequent recovery periods. Associated symptoms include sustained poor exercise performance, altered sleep patterns and appetite, frequent infections, persistent high fatigue ratings, altered immune and reproductive function, acute and chronic alterations in systemic inflammatory responses, mood disturbances (anger, depression, anxiety), and a general malaise and loss of interest in high-level training. Injuries occur more frequently in the overtrained state. The syndrome may also result from complex interactions and subsequent effects of acute and chronic alterations in systemic inflammatory responses.

Significant effects of overtraining include: (1) functional impairments in the hypothalamo-pituitary-gonadal and adrenal axis, and sympathetic neuroendocrine system as reflected by depressed urinary excretion of norepinephrine, and (2) exercise-induced increase in adrenocorticotropic hormone and growth hormone and depressed values of cortisol and insulin. In some ways the syndrome reflects the body’s attempt to enforce upon the athlete an appropriate recuperative period from the sustained levels of arousal caused by prolonged heavy training and competition. No simple, reliable method exists to diagnose overtraining in its earliest stages, although deterioration in physical performance and alterations in mood state rather than immune function changes provide the best indications. Conditions that cause some athletes to thrive in training initiate overtraining in other athletes. Generally, when symptoms emerge they persist unless the athlete rests, with complete recovery requiring weeks or even months. Currently, no reliable method exists to determine the point of complete recovery from the overtraining syndrome.


THE OVERTRAINING SYNDROME: SYMPTOMS OF STALENESS• Unexplained and persistently poor performance and high fatigue ratings• Prolonged recovery from typical training sessions or competitive events• Disturbed mood states characterized by general fatigue, apathy, depression,

irritability, and loss of competitive drive• Persistent feelings of muscle soreness and stiffness in muscles and joints• Elevated resting pulse, painful muscles, and increases susceptibility to upper

respiratory infections (altered immune function) and gastrointestinal disturbances• Insomnia• Loss of appetite, weight loss, and inability to maintain proper body weight for

competition• Overuse injuries



1. Age-predicted maximum heart rate

2. Anaerobic energy system

3. Continuous training

4. Fartlek training

5. Health-related fitness

6. HR threshold = HRrest + 0.60 (HRmax - HRrest)

7. Individual differences principle

8. Interval training

9. LSD training

10.Overload principle

11.Overtraining syndrome

12.Rating of perceived exertion (RPE)


13.Reversibility principle

14.SAID principle

15.Training-sensitive zone

STUDY QUESTIONS

Physiological Training PrinciplesList three sports requiring high levels of aerobic energy transfer and three sports requiring high levels of anaerobic energy transfer.

Aerobic Anaerobic1.

2.

3.

Overload PrincipleList four variables manipulated to achieve exercise overload.

1. 3.

2. 4.

Specificity PrincipleBriefly describe training specificity.

Individual Differences PrincipleGive one example why the principle of individual differences is important in formulating an exercise program.

Reversibility PrincipleDescribe the reversibility principle in 10 words or less (Hint: Use it or……….)


Anaerobic System Changes With TrainingList three physiologic changes that occur with sprint- and power-type training.

1. 3.

2.

Aerobic System Changes With TrainingList six specific physiologic factors that affect aerobic conditioning.

1. 4.

2. 5.

3. 6.

Metabolic MachineryList five metabolic adaptations that enhance aerobic training.

1. 4.

2 5.

3

Fat MetabolismGive two reasons for increased lipolysis with aerobic training.

1.

2.

Carbohydrate MetabolismList two reasons for enhanced carbohydrate breakdown with aerobic training.

1.

2.

Muscle Fiber Type and SizeWhich muscle fiber shows the greatest hypertrophy with aerobic training?


Cardiovascular AdaptationsList five variables that change with aerobic training and give the direction of change (+ or -)

1. 4.

2. 5.

3.

Factors That Affect the Aerobic Training ResponseList four factors that influence the response to aerobic conditioning.

1. 3.

2. 4.

Initial Level of Aerobic FitnessHow much can VO2max be expected to improve during a 12-week aerobic training program?

Training IntensityList five ways to express the exercise intensity.

1. 4.

2. 5.

3.

Train at a Percentage of HRmax

Calculate your percent VO2max training level from your age, and your ability to train at 80% of your HRmax.

Is Strenuous Training More Effective?


What is generally considered the “ceiling” training intensity for percent HRmax and percent VO2max.

% Heart rate

% VO2max

The “Training-Sensitive Zone”Calculate the predicted HRmax for the following individuals:

22 year old male

32 year old female

80 year old male

Train at a Perception of Effort.Describe the procedure to determine training intensity based on how you “feel” during exercise?

Training DurationIs there an optimal training duration per session?

Training FrequencyGive the minimum training frequency to induce a training effect.

Exercise ModeGive the optimum training mode to induce a training effect.

Trainability and GenesExplain differences between “responders” and “nonresponders” in terms of trainability.

Maintenance of Aerobic Fitness GainsIs the requirement for maintenance of aerobic fitness the same as the requirement for its improvement?


Methods of TrainingDescribe three differences between aerobic and anaerobic training.

1. 3.

2.

Anaerobic TrainingList two activities that can be used for anaerobic training.

1. 2.

Aerobic TrainingInterval TrainingWhat two factors formulate the interval training exercise prescription?

1.

2.

Continuous TrainingDefine “continuous training” and indicate the group best suited for this training method.

Definition

Group best suited

Fartlek TrainingWhat does Fartlek mean?

Overtraining: Too Much of a Good ThingDescribe three symptoms of overtraining.

1. 3.

2.


PRACTICE QUIZ1. Brief power activities lasting up to 6

sec rely on:a. ATP and PCrb. glycolysisc. aerobic metabolismd. lactic acid productione. none of the above

2. SAID:a. relates to overload principleb. relates to choosing exercise

modesc. relates to specificity principle of

trainingd. relates to reversibility principle

of traininge. none of the above

3. Exercise training:a. increases muscle fiber numberb. increases muscle fiber densityc. decreases muscle fiber numberd. changes fast to slow muscle

fiberse. none of the above

4. The most important factor affecting aerobic training response:a. initial level of fitnessb. training intensityc. training durationd. training modee. none of the above

5. Training intensity:a. can be measured in only 1 wayb. can be measured in many waysc. no minimum level necessary to

initiate a training responsed. never set below 80% of

maximum capacitye. none of he above

6. Training sensitive zone:a. refers to minimum and maximum

heart rate to illicit a training response

b. refers to maximum running speed to illicit a training response

c. refers to minimum running speed to illicit a training response

d. the same for all 18 y oldse. none of he above

7. :A type of overtraining:a. sympatheticb. neurogenicc. familiard. athletice. none of the above

8. Fartlek training:a. same as LSD trainingb. same as continuous trainingc. same as interval trainingd. originated in Spaine. none of the above

9. True or False: LSD training stands for “long slow distance training”.a. Trueb. False

10. With training maximum cardiac output:a. decreasesb. increasesc. stays the samed. increases for males and stays the

same for femalese. none of the above


LECTURE #10PHYSICAL ACTIVITY, HEALTH AND AGING

IntroductionAside from the positive effects of exercise in maintaining physiologic function, regular

physical activity protects against the ravages of this nation’s greatest killer, coronary heart disease (CHD). Individuals in physically active occupations have a two- to threefold lower risk of heart attack than individuals in sedentary jobs. Furthermore, chances of surviving a heart attack increase substantially for those with a physically demanding job or lifestyle. Physical activity also favorably modifies important CHD risk factors. Regular aerobic exercise lowers elevated blood pressure, reduces excess body fat, and improves the blood lipid profile. The blood clotting mechanism can normalize with exercise training, which reduces the chances of a blood clot forming on the roughened surface of a coronary artery. Regular exercise may also improve myocardial blood flow. This adaptation could retard the progression of heart disease, or at least maintain adequate blood supply to the heart muscle to compensate for coronary arteries narrowed by fatty deposits within their walls.

Objectives Describe the physical activity level of typical American men and women. Outline the major findings of the Surgeon General’s Report on physical activity. Answer the question: “How safe is exercise?” List important age-related changes in: (a) muscular strength, (b) joint flexibility, (c)

nervous system function, (d) cardiovascular function, (e) pulmonary function, and (f) body composition.

Describe research that shows that regular physical activity protects against disease and may even extend life.

List major risk factors for coronary heart disease, and describe how regular exercise affects each.

List factors that affect blood cholesterol level. Explain how regular physical activity reduces the risk of coronary heart disease.


The Graying of AmericaElderly persons make up the fastest growing segment of American society. Thirty years ago,

age 65 represented the onset of old age. Now gerontologists mark 85 as the demarcation of “oldest-old” and age 75 as the “young old.” Currently, nearly 12% of all Americans (about 35 million) exceed age 65 and by the year 2030, 70 million Americans will exceed age 85. Some demographers project that one-half of the girls and one-third of the boys born in developed countries near the end of the 20th century actually will live in three centuries. In the short term, disease prevention, health care, and more effective treatment of age-related diseases like heart disease and osteoporosis continue the advances in longevity. Far fewer people now die from infectious childhood diseases, so those with the genetic potential actualize their proclivity for longevity.

Centenarians currently represent proportionately the fastest growing age group in the United States. Numbers range between 30,000 and 50,000, up from the estimate of 15,000 in 1980 and almost none at beginning of the 20th century. No longer viewed as a quirk of nature, 1 in 10,000 Americans live to the age of 100. Demographers project that by the middle of the next century more than 800,000 Americans will exceed age 100, with many of these men and women remaining in relatively good health. Old-age mortality actually appears on the decline in that the death rate (number of people per 100 in a specific age group) levels off in the 90-year-old age category (approximately 11 per 100) and decreases to 8 per 100 after age 100! On a disturbing front, the Centers for Disease Control and Prevention reports that nearly one in ten Americans over age 70 needs help with daily activities such as bathing and four in ten use assistive devices such as walkers or hearing aides. In addition, about one-half of men and two-thirds of women older than age 70 have arthritis; one-third of all Americans in this age group also have high blood pressure and 11% have diabetes. Of all seniors, women over age 85 are the most likely to need everyday help, with 23% requiring assistance with at least one basic activity (e.g., dressing or going to the toilet).

The New GerontologyGenes exert strong influence over life span, patterns of aging, and susceptibility to disease.

Yet scientists know little why humans live five times longer than cats, cats five times longer than mice, mice outlive fruit flies by a factor of 25, or why the onset of different diseases (e.g., Alzheimer’s disease) often differ by many years in identical twins.

The contribution of genetics to the unprecedented increase in human life expectancy remains unanswered. In the early 1900s, for example, 4% of the U.S. population exceeded 65 years of age. By 1998, that percentage increased to 13%. A citizen’s average life expectancy has increased from 47 years in 1900 to 76 years today, and should reach 83 years by the year 2050. Sixty-three percent of today’s 65-year-olds will achieve their 85th birthday, and 24% will celebrate age 95. Researchers now believe that the average child born today may readily live healthfully to age 95 or 100, with the limit of human life span currently estimated at 130 years.

Improved overall health accompanies extended life span. The prevalence of chronic disorders (e.g., arthritis, dementia, hypertension, stroke, and emphysema) continues to decline. Eighty-nine percent of Americans age 65 to 74 years reports no disability; even after 85 years of age, 4% remain fully functional. A decline in the population of elders living in nursing homes (6.3% in 1982 to 5.2% in 1998) accompanies the upgraded functional status of the elderly. Concurrently, a “new gerontology” expands the focus on aging from preoccupation with disease and frailty to a more positive, notion of “successful aging.”

The Concept of “Healthspan” and “Successful Aging”The aging process, including the development of physical frailty towards the last decade of

life, traditionally has been viewed as physiologically inevitable. The typical “aging syndrome” includes a constellation of chronological age-related and/or lifestyle-dependent deleterious


changes in blood pressure, bone mass, body composition and body fat distribution, insulin sensitivity, and homocysteine levels that convey increased health risk, dysfunction, or actual disease. This traditional view has changed dramatically; it now seems evident that chronological aging does not conform to a grim stereotype of unalterable decline and loss of body structure and functional capacity. As more people reach that “ripe old age,” the concept of successful aging encompasses more than just the avoidance or delay of disease. Successful aging entails maintenance and even enhancement of physical and cognitive functions. It requires full engagement in life, including productive activities and interpersonal relations.

To a large extent, lifestyle changes that include sound nutrition and diverse forms of exercise substantially blunt the decline in function and increased disease risk with aging. The lack of muscle strength often limits an increasing number of the healthy elderly’s chances to live a full, independent, and productive life into the ninth and tenth decade. In a study of 100 frail nursing home residents (average age 87 years), resistance training for only 45 minutes, three times weekly for ten weeks doubled muscular strength and improved gait and stair climbing. Such findings demonstrate the substantial responsiveness of the healthy human body at any age to regular exercise.

Many gerontologists maintain that research on aging must focus not simply on increasing lifespan but rather improving “healthspan,” the total number of years a person remains in excellent health. Researchers now view much of the physiologic deterioration previously considered as “normal aging” as dependent on lifestyle and environmental influences subject to significant modification with proper diet and exercise. For those achieving older age, poor muscular strength, cardiovascular function, and joint range of motion as well as sleep disturbances link directly to functional limitations regardless of disease status.

Physical Activity EpidemiologyEpidemiology involves quantifying factors that influence the occurrence of illness to

ultimately better understand, modify, and/or control a disease pattern in the general population. The specific field of physical activity epidemiology applies the general research strategies of epidemiology to study the association of physical activity as a health-related behavior with disease and other outcomes.38

TERMINOLOGY

Physical activity epidemiology applies specific definitions to characterize behavioral patterns and outcomes of the groups under investigation. Examples of relevant terminology include:

Physical activity: Body movement produced by muscle action that increases energy expenditure.

Exercise: Planned, structured, repetitive, and purposeful physical activity. Physical fitness: Attributes related to one’s ability to perform physical activity. Health: Physical, mental, and social well being, not simply the absence of disease. Health-related physical fitness: Components of physical fitness associated with some

aspect of good health and/or disease prevention include cardiovascular fitness, abdominal muscular strength and endurance, optimal body composition, flexibility of the lower back and hamstrings.

Longevity: Length of life.Within this framework, physical activity becomes a generic term and exercise comprises the

major component. Similarly, the definition of health focuses on the broad spectrum of well being that ranges from the complete absence of health (death) to the highest levels of physiological function. Such definitions often challenge our ability to objectively measure and


quantify. However, they do provide the broad frame of reference to study the role of physical activity and exercise in health and disease.

Surgeon General’s Report On Physical Activity and HealthThe Surgeon General of the United States acknowledged the importance of physical activity

in 1996 in a wide-ranging report summarizing the benefits of physical activity in disease prevention. The conclusions and recommendations of this hallmark report apply to all individuals interested in health improvement. In essence, the Surgeon General proposed a national agenda that urges the nation to adopt and maintain a physically active lifestyle to combat the increasing number of physical ailments associated with the country’s generally low level of energy expenditure. Hopefully, this document will generate as great an impact as the 1964 Surgeon General’s Report on the hazards of smoking.

The Report focuses on three objectives:1. Summarize existing literature relating regular physical activity to disease prevention2. Evaluate current status of physical activity in the population3. Stimulate increased physical activity among Americans of all ages.

Concerning benefits of regular physical activity, the Report concludes1. Almost everyone derives overall health benefits from participation in regular physical activity

2. Significant health and quality of life benefits emerge with only moderate, daily physical activity (e.g., 30 minutes brisk walking or raking leaves, 15 minutes running, or 45 minutes playing volleyball)

People who maintain a regular regimen of vigorous activity of longer duration obtain the greatest health-related benefits

Regular physical activity reduces general premature mortality risk, and specific risks of coronary heart disease, hypertension, osteoporosis, colon cancer, and adult-onset diabetes. It also enhances overall mental well being, and contributes to optimal neuromuscular-skeletal functioning.

For Your InformationPhysical Activity Levels of Adults and Children in the USA

Adults•• 15% of adults engage in regular vigorous

physical activity during leisure time (3/wk for at least 20 min)

•• 22%of adults engage regularly in light-to-moderate physical activity during leisure time (5/wk for at least 30 min)

•• More than 60% of American adults do not engage regularly in physical activity; 25% lead sedentary lives

•• Physical inactivity occurs more among women than men, blacks and Hispanics than whites, older than younger adults, and less affluent than wealthier persons

•• Walking, gardening, and yard work represent the most popular leisure-time activities for adults

•• Participation in fitness activities declines with age. A large number of older citizens have such poor functional capacity that they cannot raise from a chair or bed, walk to the bathroom, or climb stairs without assistance

Children and Teenagers•• Nearly one-half between ages 12 and 21 •• 25% engage in light to moderate physical

Figure 1. Generalized curve to illustrate age-related changes in physiologic function. All comparisons made against the 100% value achieved by the 20- to 30-year-old sedentary person.


yrs do not vigorously exercise on a regular basis; a sharp decline in physical activity occurs during adolescence

activity nearly every day (e.g., walk or bicycle)

•• 14% report no recent physical activity (more prevalent among females, particularly black)

•• More males participate in vigorous physical activity, strengthening activities, and walking or bicycling than females

•• Participation in all types of physical activity declines strikingly as age and school grade increase

•• Daily attendance in school physical education programs declined from 42% in early 1990 to only 25% in 1996

•• 19% of high school students report being physically active for at least 20 min in daily physical education classes

SAFETY OF EXERCISINGPeople have questioned the safety of exercise because of several well-publicized reports of

sudden death during physical activity. Actually, sudden death rates during exercise have declined over the past 20 years despite an overall increase in exercise participation. In one report of cardiovascular episodes over a five-year period, 2935 exercisers recorded 374,798 exercise hours that included 2,726,272 km (1.7 million miles) of running and walking. No deaths occurred during this time (with only two nonfatal cardiovascular complications). Certainly, a small increased risk of a cardiovascular episode during exercise exists compared to resting. However, the total reduction in heart disease risk from regular physical activity (compared with remaining sedentary) far outweighs any slight increase in risk during the actual exercise.

Perhaps not surprisingly, musculoskeletal injury represents the most prevalent exercise complications. For 351 participants and 60 instructors at six aerobic dance facilities, 327 medical complaints were reported during nearly 30,000 hours of activity. Eighty-four of the injuries caused disability (2.8 per 1000 person-hours of participation), and only 2.1% of the injuries required medical attention. The greatest orthopedic injury potential for jogging and running activities exists among individuals who exercise for extended durations: more is certainly not better.

Aging and Bodily FunctionFigure 1 shows that various bodily functions generally improve rapidly during childhood to

reach a maximum between age 20 and 30 years; thereafter, a general decline in functional capacity occurs with advancing age. Although a similar age trend exists for the physically active, physiologic function averages about 25% higher compared with the sedentary at each age category (an active 50-year old man or woman often maintains the functional level of a 30-year-old). Although all physiological measures eventually decline with age, not all decrease at the same rate. Considerable variation exists from person-to-person, and from biologic system-to-biologic system

within the same person.


Nerve conduction velocity, for example, declines only 10 to 15% from 30 to 80 years of age, whereas resting cardiac index (ratio of cardiac output to surface area) and joint flexibility decline 20 to 30%; maximum breathing capacity at age 80 averages 40% of values for a 30-year-old. Brain cells die at a fairly constant rate until age 60, while liver and kidneys lose 40 to 50% of their function between ages 30 and 70. By the seventh decade, the average female has lost 30% of bone mass, while men only 15%. Gerontologists have often considered these aging patterns to represent the “normal” and “expected” decreases in structure and function.

Aging and Muscular StrengthMen and women generally achieve maximum strength between ages 20 to 30 years, when

muscular cross-sectional area achieves maximum size. Thereafter, strength progressively declines for most muscle groups, so by age 70 a 30% decrement occurs in overall strength.

Decrease in Muscle MassReduced muscle mass represents the primary factor responsible for age-associated strength

decreases. The smaller muscle mass reflects a loss of total muscle protein induced by inactivity, aging, or the combined effects of both. Some loss in muscle fiber number also takes place with aging. For example, the biceps muscle of a newborn contains about 500,000 individual fibers, while the same muscle for a man age 80 has 300,000 fibers or 40% less.

Muscle Trainability Among the ElderlyRegular exercise training facilitates protein retention and blunts the loss of muscle mass

and strength with aging. Healthy men between age 60 and 72 years who participated in a 12-week standard resistance training program showed that muscle strength increased progressively throughout the program, averaging about 5% each exercise session – a training response similar to young adults. Many exercise specialists who work with the elderly maintain that improving strength represents a highly effective way to maintain muscle mass, increase mobility, and reduce injury incidence.

Aging and Joint FlexibilityWith advancing age, connective tissue (cartilage, ligaments, and tendons) becomes stiffer

and more rigid, which reduces joint flexibility. It remains uncertain whether these changes result from biologic aging per se or reflect the impact of chronic disuse through sedentary living and/or degenerative tissue diseases of specific joints. Regardless of the cause, appropriate exercises that regularly move joints through their full range of motion increase flexibility 20 to 50% in men and women at all ages.

Endocrine Changes With AgingPart of the aging process relates altered endocrine function, particularly the pituitary,

pancreas, adrenal, and thyroid glands. About 40% of individuals aged 65 and 75 years, and 50% of those older than age 80, have impaired glucose tolerance leading to non-insulin dependent diabetes (adult-onset or type 2 diabetes). This represents the most common form of the disease and afflicts 1 in 17 Americans; nearly one-half of these cases remain undiagnosed. Impaired glucose metabolism leading to high blood glucose levels in type II diabetes results from:

Decreased effect of insulin on peripheral tissue (insulin resistance) Inadequate insulin production by the pancreas to control blood sugar (relative insulin

deficiency) Combined effect of the above


These factors are influenced by genetic predisposition, obesity, sedentary lifestyle and aging.

Aging and Nervous System FunctionA 37% decline in number of spinal cord axons and a 10% decline in nerve conduction

velocity reflect cumulative effects of aging on central nervous system function. Such changes partially explain the age-related decrements in neuromuscular performance. Partitioning reaction time into central processing time and muscle contraction time indicates that aging most affects stimulus detection and information processing to produce a response.

Aging and Pulmonary FunctionWhether regular exercise throughout one’s life overrides pulmonary system “aging”

remains unknown. Cross-sectional studies indicate that dynamic pulmonary capacity of older endurance-trained athletes exceeds that of sedentary peers. Although longitudinal studies will provide a definitive answer, available data suggests that regular physical activity retards pulmonary function deterioration associated with aging.

Aging and Cardiovascular FunctionDifferent indices of cardiovascular function decline with age. Below, we review some of

these changes and the effects of exercise on altering the rate of decline.

Maximal Oxygen UptakeMaximal oxygen uptake (VO2max) declines steadily after age 20, decreasing by 35 to 40% at

age 65 (slightly less than 1% per year). A slower rate of decline occurs for individuals who maintain an active lifestyle that includes regular aerobic training , without a decline in fat-free body mass. Physical activity, however, does not entirely prevent aging’s effect on VO2max, even when adjusting for a person’s quantity of muscle.

Deterioration in VO2max with aging probably results from cumulative effects including age-associated loss of muscle mass, increases in body fat, and altered cardiovascular and pulmonary functions. The reductions in aerobic power per kg of active muscle with aging can only reflect reduced oxygen delivery and/or reduced oxygen extraction at the active muscle. In contrast, skeletal muscle oxidative capacity and capillarization remain similar in older and younger individuals with comparable physiologic characteristics and training histories. The well-documented reduction in cardiac output (both maximum heart rate and stroke volume) represents the most likely explanation for the decrease in VO2max per kg of active muscle accompanying aging.

A System Responsive to Training at Any AgeAmong the healthy elderly, exercise training enhances the heart’s capacity to pump blood

and increases aerobic capacity to the same relative degree as younger adults. Nine to 12 months of endurance training in healthy older adults increased VO2max 19% in men and 22% in women. These values represent the high end of the typical training response for young adults. Regular aerobic training for middle-aged men over a 20-year period significantly delayed the usual 10 to 15% decline in exercise capacity and aerobic fitness. At age 55, these active men maintained nearly the same values for blood pressure, body mass, and VO2max as at age 35; by age 70, their VO2max equaled values for individuals 25 years younger! These remarkable findings attest to the adaptability of the aerobic system to training at any age.

Figure 2. World record marathon times for men and women of different ages.


Aging and Endurance PerformanceComparing endurance performance times among individuals of different ages points up the

dramatic effects of exercise training on preserving cardiovascular function throughout life. Figure 2 shows the world-record marathon times for males and females of different ages, starting at about age 4 and into the mid-80s (the world record was just set on April 1, 2002; 2:05:38, not shown here.)

The world record time of 340.2 minutes for the 86-year old male corresponds to a 12.9 min per mile pace; for the-80 year old female, the world record time equals 328.6 (12.5 min per mile pace.) This represents a remarkable 26.2-mile average running speed for men and women in their eighth decade of life. Performances of this quality attest to the tremendous cardiovascular capabilities of the healthy elderly who continue to train regularly as they grow older.

Aging and Body CompositionExcess body fat accumulation usually begins in childhood or develops slowly during

adulthood. Middle-aged men and women invariably weigh more than their college-age counterparts of the same stature (with differences in body fat accounting for the weight difference). Scientists do not know if gains in body fat during adulthood represent a normal biologic pattern. Observations of physically active older individuals suggest that, while the typical individual grows fatter with age, those who remain physically active counter the normal loss in fat-free body mass without increasing body fat percentage.

Figure 3 (next page) shows how body composition changes over a 20-year period for 21 elite master’s runners. Despite maintaining a relatively constant body mass during the prolonged period of exercise training (T1=70.1 kg; T2 = 69.4 kg; T3 = 70.8 kg), gains occurred in body fat and fat-free body mass declined. The roughly 3% body fat unit increase per decade paralleled similar increases in waist girth. These data support an argument that some alterations in body composition and body fat distribution represent a normal aging response.

Regular Exercise: A Fountain Of Youth?Although exercise may not necessarily represent a “fountain of youth,” regular physical

activity not only retards the decline in functional capacity associated with aging and disuse, but often reverses the loss of function regardless of when a person becomes active.

Figure 4. Reduced risk of death with regular exercise.

Figure 3. Changes in percent body fat (D) and (E) fat-free body mass for 21 endurance athletes who continued to train over a 20-year period, starting at age 50.


Medical experts have debated if a lifetime of regular exercise contributes to good health and perhaps longevity compared with a sedentary “good life.” Because older fit individuals exhibit many functional characteristics of younger people, one could argue that improved physical fitness and a vigorous lifestyle retards biological aging and confers health benefits later in life.

One group of researchers investigated the diseases and longevity of former college athletes. This seemed like an excellent group with which to study possible links between exercise and longevity, because collegiate athletes usually have longer involvement in habitual physical activity prior to entering college than nonathletes, and they may remain more physically active following graduation. These and more recent findings suggest that participation in athletics as a young adult does not assure

significant longevity.

Enhanced Quality To Longer Life: Harvard Alumni StudyResearch concerning current lifestyles and exercise habits of 17,000 Harvard alumni who

entered college between 1916 and 1950 indicates that only moderate aerobic exercise, equivalent to jogging three miles a day, promotes good health and longevity. Men who expended 2000 kCal weekly had up to one-third lower death rates than classmates who did little or no exercise. To achieve a 2000 kCal energy output weekly requires moderate additional physical activity such as a daily 30 to 45-minute brisk walk, run, cycle, swim, cross country ski, or aerobic dance. The following summarizes the results of the study of alumni:

Regular exercise counters the life-shortening effects of cigarette smoking and excess body weight

Even for people with high blood pressure (a primary heart disease risk), those who exercised regularly reduced their death rate by one-half

Regular exercise countered genetic


tendencies toward an early death. For individuals who had one or both parents die before age 65 (another significant risk), a lifestyle that included regular exercise reduced the risk of death by 25%

A 50% reduction in mortality rate occurred for those whose parents lived beyond 65 yearsFigure 4 (previous page) shows that among physically active people, a person who exercises

more has a reduced risk of death. For example, men who walked 9 or more miles a week showed a 21% lower mortality rate than men who walked 3 miles or less. Exercising in light sports activities increased life expectancy 24% over men who remained sedentary. From a perspective of energy expenditure, the life expectancy of Harvard alumni increased steadily from a weekly exercise energy output of 500 kcal to 3500 kcal, the equivalent of six to eight hours of strenuous weekly exercise. In addition, active men lived an average of one to two years longer than sedentary classmates. (Other research estimates a life expectancy increase of about 10 months with regular exercise.)

No additional health or longevity benefits accrued beyond weekly exercise of 3500 kcal. Men who performed extreme exercise actually had higher death rates than less active colleagues (another example of why more does not necessarily indicate better exercise benefits).

Improved Fitness: A Little Goes a Long WayA study of more than 13,000 men and women over an eight-year interval indicates that even

modest amounts of exercise substantially reduce the risk of death from heart disease, cancer, and other causes. The study evaluated fitness performance by directly, rather than relying on verbal or written reports of regular physical activity habits. To isolate the effect of physical fitness per se, the researchers considered factors of smoking, cholesterol and blood sugar levels, blood pressure, and family history of coronary heart disease. Figure 5 (below) , based on age-adjusted death rates per 10,000 person-years, illustrates that the least fit group died at a three-times greater rate than the most fit subjects.

The most striking finding was that the group rated just above the most sedentary category derived the greatest health benefits. The decrease in death rate for men from the least fit to the next category equaled 38 (64.0 vs. 25.5 deaths per 10,000 person-year), whereas the decline from the second group to the most fit category equaled only seven. Women obtained similar benefits as men. The amount of exercise required to move from the most sedentary category to the next more fit category (the jump showing the greatest health benefits) occurred for moderate-intensity exercise like walking briskly for 30 minutes several times weekly. According to available evidence, if life-extending benefits of exercise exist, they are associated more with preventing early mortality than improving overall life span. While the

Figure 5. Physical fitness and longevity. The greatest reduction in death rate risk occurs when going from the most sedentary category to a moderate fitness level.

Figure 6. [Left] Cross section of a normal coronary artery. [Right], deterioration of coronary artery in atherosclerosis; deposits of fatty substance roughen the vessel’s center.


maximum life span may not extend greatly, more active people survive to a “ripe old age” with only moderate exercise.

Coronary Heart Disease1.5 million Americans will have a heart attack this year and about one-third of them will die.

While deaths from CHD have declined more than 35% since 1970, heart disease still remains the leading cause of death in the Western world. Although death rates for women lag about 10 years behind men, the gap has closed fast, particularly for women who smoke. For every American who dies of cancer, nearly three die of heart-related diseases. This health disaster produces staggering economic losses – $130 billion in 1996 from medical costs, loss of earnings, and lost productivity. And this does not include the emotional impact of losing a loved one in the prime of life.

A Life-Long ProcessAlmost all people show some evidence of CHD, which can be severe in seemingly healthy

young adults. This degenerative process probably begins early in life, as fatty streaks emerge in the coronary arteries of children as young as age five. Little harm exists for most people until the coronary arteries become markedly narrowed. Figure 6 shows that atherosclerosis involves degenerative changes in the inner lining of the arteries that supply the heart muscle.

The action and chemical modification of various compounds, including oxidation of cholesterol in low-density lipoproteins, initiates a complex process that ultimately causes bulging lesions in the arterial wall. The lesions initially take the

form of fatty streaks. With further damage and proliferation of underlying smooth muscle cells, vessels progressively congest with lipid-filled plaques, fibrous scar tissue, or both. This change reduces the vessels’ capacity for flood flow, causing the myocardium to receive diminished oxygen (ischemia) from inadequate blood flow.

The roughened, hardened lining of the artery frequently causes the slowly flowing blood to clot. When a blood clot (thrombus) forms, it plugs one of the smaller coronary vessels, causing necrosis (death) of a portion of the myocardium. When this occurs, the person can suffer a heart attack or myocardial infarction. With only moderate blockage (but with blood flow reduced below the heart’s requirement), the person may experience temporary chest pain termed angina pectoris. The pains usually magnify during exertion because increased physical activity causes a great demand for myocardial blood flow. Angina attacks provide vivid evidence of the importance of adequate oxygen supply to the myocardium.

Women at RiskWomen have increased their risk for developing CHD. Since 1910, more American women

have died of heart disease than any other cause. Because women develop heart disease 10 to 15 years later in life than men, they more likely have heart attacks when past middle age. Only


1% of women under age 45 develop CHD, while 13% above age 75 show clinical heart disease manifestations. This sex-age difference in heart disease episodes makes CHD appear as a more pervasive and dramatic problem in men; a heart attack for a 75-year-old woman seems less shocking than for a male “wage earner” who suffers an attack in the prime of life. Increased CHD for women in later years partly relates to loss of protection offered by estrogen, which declines markedly after menopause. Despite limited heart disease research on women, available evidence indicates that disease symptoms, progression, and outcome differ in women and men. Some interesting sex-related heart disease differences include:

Following a heart attack, women usually die sooner Women who survive a heart attack frequently experience a second episode Women become more incapacitated by heart disease-related pain and disability Women are less likely to survive coronary artery by-pass surgerySeveral factors seem clear: A similar process probably exists for CHD development in men

and women, i.e., fatty deposits narrow coronary arteries and reduce blood flow to the myocardium. Hormonal differences may also affect blood clot formation, coronary artery smooth muscle cell proliferation, and the tendency of coronary vascular walls to spasm in the final stages preceding a heart attack. Moreover, CHD diagnosis may differ in women and men. Diagnostic tests, like the treadmill stress test and ECG response, have limited use with women because men have provided the subject pool for test validation. A diagnostic gap also occurs because some physicians do not treat heart disease signs in women as aggressively as in men. Consequently, they do not prescribe coronary angiography (the most valid way to diagnose CHD) as often following a positive stress test.

Despite a lower CHD risk, premenopausal women are not immune from heart disease, particularly if they smoke. Cigarette smoking accounts for almost one-half of all heart attacks in women before age 55. Smoking as few as four cigarettes daily doubles a women’s CHD risk. Hypertension also exists in more than 50% of women over age 55 who suffer a heart attack; after age 65 it affects two-thirds of female victims. Elevated blood sugar afflicts women more often than men. The presence of either Type 1 or Type 2 diabetes raises a woman’s CHD risk to equal that for a nondiabetic man of the same age, and puts her risk of dying from a heart attack even greater than the man’s. Use of birth-control pills also raises a woman’s CHD risk.

Risk Factors For Coronary Heart DiseaseVarious personal characteristics and environmental factors identified over the past 45 years

indicate a person’s susceptibility to CHD. In general, the greater the number of the risk factors, the more likely coronary artery disease exists or will emerge in the near future. This does not mean that a specific risk factor causes disease, as diverse factors may act and interact in a cause-and-effect manner. However, risk factor identification and prudent modification improves an individual’s chances to avoid CHD.

The following risk factors can be modified:1. Cigarette smoking2. Physical inactivity3. Hypertension4. Elevated blood lipids5. Abdominal-visceral

adiposity6. Diabetes mellitus7. Obesity8. High fat diet

9. ECG abnormalities10. Elevated homocysteine levels11. High-strung, nervous personality12. Psychosocial characteristics of work

(e.g., low job control and low pay)13. High uric acid levels14. Pulmonary function abnormalities15. Tension and stress


The following risk factors are considered fixed, i.e., they cannot be modified.1. Age 2. Gender3. Heredity

4. Race5. Male pattern baldness


>130 mg•dL-1 (3.4 mmol•L-1)130-159 mg•dL-1 (3.4-4.1 mmol•L-1)< 160 mg•dL-1 (4.1 mmol•L-1)

DesirableBorderline highHigh

HDL Cholesterol Classification

>35 mg•dL-1 (0.9 mmol•L-1) Low

Table 2. Serum triglyceride classifications

Serum Triglycerides Classification Comments

>200 mg•dL-1 Normal

200-400 mg•dL-1 Borderline highCheck for

accompanying dyslipidemias

400-1000 mg•dL-1 High

Check for accompanying dyslipidemias

<1000 mg•dL-1 Very high Increased risk for acute pancreatitis

Importance of Cholesterol FormsCholesterol and triglycerides represent the two most common lipids associated with CHD

risk. Recall from Lecture 3 that these lipids remain insoluble in water so they do not circulate freely in blood plasma. Rather, they transport combined with a carrier protein to form a lipoprotein. This lipoprotein varies in size depending on the quantity of protein and lipid it contains. Hyperlipidemia refers to a general elevation in blood lipids, while hyperlipoproteinemia more meaningfully describes elevation in the specific lipoproteins.

The distribution of cholesterol among various lipoproteins more powerfully predicts heart disease than total plasma lipids. This helps to explain how one person with a high total cholesterol may not develop CHD, while it develops in another person with lower cholesterol. Specifically, elevated high-density lipoproteins (HDL), which contain the largest quantity of protein and least cholesterol, relate to low heart disease risk. In contrast, elevated cholesterol-rich low-density lipoproteins (LDL) represent an increased risk.


RISK FACTORS IN CHILDREN AND ADOLESCENTSMultiple CHD risk factors (obesity, elevated blood lipids, physical inactivity, cigarette smoking, and a family history of heart disease) frequently occur in young children and adolescents. In addition, the risks often interrelate as the fattest children generally have the highest cholesterol and triglyceride levels and lowest of physical activity levels. Schools must initiate programs aimed at reducing risk factors in children and adolescents, but current efforts have fallen short, particularly regarding tobacco use. The 1998 Youth Risk Behavior Study from the Centers for Disease Control and Prevention reported that cigarette use among black, white, and Hispanic high school students jumped considerably between 1991 and 1997. Moreover, there was a precipitous 80% increase from 1991 to 1997 in percentage of black males who smoked. The tobacco industry’s advertising and marketing campaign to attract new smokers (coupled with renewed glamorization of tobacco products in movies, TV, and music videos) apparently overwhelm school efforts at risk intervention at an early age.


LDL transports cholesterol throughout the body for delivery to cells, including those of the arteries’ smooth muscle walls. It oxidizes there and ultimately contributes to the artery-narrowing process of atherosclerosis. Whereas LDL carries cholesterol to tissues and contributes to arterial damage, HDL acts as a scavenger, gathering cholesterol from cells (including cells in arterial walls) and returning it for metabolism to the liver and excretion in the bile.

Research continues to clarify HDL’s protective effect and what factors raise its levels. For one thing, cigarette smoking adversely affects plasma HDL concentrations. This may account for the significant CHD risk with smoking. From an exercise perspective, endurance athlete’s posses’ relatively high HDL levels; favorable alterations also occur in sedentary people who engage in either moderate or vigorous aerobic training. Concurrently, exercise decreases LDL, which produces the net effect of a considerably improved ratio of HDL-to-LDL, or HDL-to-total cholesterol. The exercise effect occurs independent of the diet’s lipid content or the exerciser’s body composition. Moderate consumption of alcohol (equivalent to about 2 oz. or 30 mL of 90 proof alcohol, three 6 oz. glasses of wine, or a bit less than three 12 oz. cans of beer) reduces an otherwise healthy person’s risk of heart attack. The cardioprotective mechanism may relate to alcohol’s effect in raising HDL and lowering LDL, and blunting arterial smooth muscle cell proliferation. Excessive alcohol consumption offers no lipoprotein benefit; it also greatly increases risk of liver disease and cancer.

Factors That Affect Cholesterol and Lipoprotein LevelsDifferent variables affect cholesterol and lipoprotein levels. Variables that cause favorable

effects include:

Weight loss (through food restriction or exercise)

Regular aerobic exercise (independent of weight loss)

Increased intake of water-soluble fibers (e.g., fibers in beans, legumes, and oat bran)

Increased dietary polyunsaturated to saturated fatty acid ratio and monounsaturated fatty acids

Increased intake of unique polyunsaturated fats in fish oils

Moderate alcohol consumptionVariables that cause undesirable effects

include:Cigarette smokingDiet high in saturated fat and preformed

cholesterolEmotionally stressful situationsCertain oral contraceptivesSedentary lifestyleObesityPhysical Activity

CHOLESTEROL RATIOS IMPORTANT?An effective way to evaluate lipoprotein status divides total cholesterol by HDL cholesterol. This ratio represents a superior index of heart disease risk than either total cholesterol or LDL-cholesterol level. An HDL:Cholesterol ratio greater than 4.5 indicates high risk for heart disease, whereas an optimal ratio equals 3.5 or lower.

FOR YOUR INFORMATIONSHOULD CHILDREN HAVE CHOLESTEROL MEASURED?Guidelines issued by the National Cholesterol Education Program conclude “yes” if a family history of high cholesterol or heart disease exists (particularly if a parent suffered a heart attack before age 50). Shockingly, this parental “cardiac proneness” includes up to one-fourth of the United States adult population! Research with children aged 10 to 15 years indicates that lifestyle habits like regular exercise, improved cardiovascular fitness, and a prudent nutritional profile contribute to favorable lipid profiles similar to effects seen with adults.



A critique of 43 studies of the relationship between physical inactivity and CHD concluded that lack of regular exercise contributes to heart disease in a cause-and-effect manner, with the sedentary person at almost twice the risk as the most active individual. The strength of this protective association equaled that observed between CHD and hypertension, cigarette smoking, and high serum cholesterol. This places physical inactivity as the greater heart disease risk, considering that more people lead sedentary lives than have one or more of the other risks. Although vigorous exercise does entail a small risk of sudden death during the activity, the important longer-term health benefits of regular physical activity far outweigh any potential acute risk.

HypertensionMore than 35 million Americans currently have systolic blood pressures over 140 mm Hg

(systolic hypertension) or diastolic pressures that exceed 90 mm Hg (diastolic hypertension). These values form the lower limit for the classification of borderline high blood pressure. One out of every five people experience chronic abnormally high blood pressure sometime during their lives. Uncorrected hypertension leads to heart failure, heart attack, stroke, or kidney failure.

Hypertension, often labeled the “silent killer,” generally progresses unnoticed for decades before inflicting its deadly blow. The cause(s) of hypertension remains unknown in more than 90% of cases. Statistics indicate that the optimal blood pressure for longevity averages about 110 mm Hg systolic and 70 mm Hg diastolic. Anything higher results in increased cardiovascular disease risk. For example, a man with systolic blood pressure above 150 mm Hg has more than twice the heart disease risk as someone with 120 mm Hg. Many people have a genetic predisposition toward hypertension that increases their tendency to retain salt, heightens the reactivity of their blood vessels to stress, and causes higher levels of chemicals that constrict peripheral vasculature.

Cigarette SmokingIn terms of health status, the more a person smokes, the poorer the future health status.

Cigarette smoking represents one of the strongest predictors of CHD. In fact, the probability of death from heart disease for smokers nearly doubles compared to nonsmokers. Risk for CHD (and lung cancer) increases the more one smokes, the deeper one inhales, and the stronger the cigarette’s tars and noxious by-products. Also, smokers experience nearly 5 times the risk for stroke as nonsmokers, and those who smoke a pack or more a day have an 11-times greater chance of suffering a specific type of sudden, deadly stroke that strikes younger men and women.

Surprisingly, CHD risk from smoking translates to two to three times more deaths than excess mortality from lung cancer. Even exposure to second-hand smoke increases CHD risk. Three hours of second-hand smoke exposure equals smoking one pack of cigarettes. The good news: if a smoker for 40 years stops, CHD risk returns to that of a “never smoker” within five years, regardless of age.

ObesityObesity’s association with many diseases makes the quantitative importance of excess body

fat per se as a health risk difficult to determine. However, the death rate for men weighing 30% in excess of ideal weight exceeds the risk for a normal-weight individuals by 70%. The overfat condition often accompanies multiple risk factors like hypertension and elevated serum lipids. In addition, an obese person usually consumes a highly atherogenic diet rich in saturated fatty acids and cholesterol. Gaining weight also increases chances for developing impaired glucose tolerance (type 2 diabetes).

Weight loss and accompanying body fat reduction generally contribute to normalizing plasma cholesterol and triglycerides, and exert beneficial effects on blood pressure and type 2


diabetes. Age-related gains in body mass partly explain the expected increase in blood pressure with age. Obesity does not rate as a primary CHD risk factor, yet one cannot deny its role as an important contributing factor.

Personality and Behavior PatternsA distinct personality susceptible to heart disease may exist. The coronary-prone behaviors

(hard-driving, ambitious, impatient, short-tempered, hostile, and restless) typify what psychologists call the Type A personality. Unrelenting pressures, drives, deadlines, anxieties, depression, and a constant struggle against the limitations of time comprise the Type A stress syndrome, with its accompanying excessive stimulation of the body’s “fight or flight” hormonal response, which may impair cardiovascular health.

The opposite style, exemplified by the equally capable but easy going, no pressure, “laid back” Type B personality, functions under no time pressure. The absence of Type A behaviors characterizes this personality type. Generally, most people classify as neither all Type A nor all Type B, but rather a blend of both patterns.

The precise manner in which personality and behavior influence CHD development remains unknown, let alone whether one’s basic personality “type” can significantly influence a disease process. One desirable strategy would recognize, manage, and effectively direct excess stress elsewhere. To this end, regular exercise blended with behavior modification can channel potentially harmful behaviors into ones that produce positive “spin-off.” Interestingly, laughter may play an important role in the stress response and positively influence disease processes. Individuals who laugh easily, spontaneously, and hard on a regular basis have lower CHD incidence, recover faster from surgery, and generally remain less susceptible to disease.

FOR YOUR INFORMATIONEXERCISE IS GOOD MEDICINEStudies of the health and exercise habits of Harvard alumni indicate that physically active men had about one-half the risk of colon cancer as inactive classmates. The protection disappeared if the men stopped exercising. One mechanism proposes that exercise protects against cancer by speeding passage of food residues through the digestive tract, this reduces the colon’s exposure to potential carcinogens in food.


LECTURE #10STUDY GUIDE


1. Atherosclerosis

2. Borderline hypertension

3. CHD risk factors

4. Coronary heart disease

5. Harvard alumni study

6. Heart attack

7. High-density lipoproteins

8. Hyperlipidemia

9. Hyperlipoproteinemia

10.Low-density lipoproteins

11.Myocardial infarction


12.Primary CHD risk factors

13.Surgeon General’s Report on Physical Activity and Health

14.Systolic hypertension

15.Modifiable risk factors

16.Type A personality

17.Type B personality

STUDY QUESTIONS

The Graying of AmericaGive 2“facts” about the aging of our population.

1.

2.

Physical Activity EpidemiologyDescribe differences between the concepts of exercise and physical activity.

The New GerontologyHow long can one expect to live healthfully?

The Concept of Healthspan and Successful AgingDescribe “healthspan”.


Describe “successful aging”.

Physical Activity EpidemiologyDescribe the differences between the terms exercise and physical activity.

Surgeon General’s Report On Physical Activity and HealthList the three objectives of the Surgeon General’s Report on Physical Activity.

1. 3.

2.

Safety of ExercisingWhat is the most prevalent injury caused by exercise.

Aging and Bodily FunctionAt what age does “aging” seem to occur?

Aging and Muscular StrengthHow much loss of muscular strength occurs by age 70?

Decrease in Muscle MassReduced muscle mass triggers what age-associated decrease in physiologic function?

Muscle Trainability Among the ElderlyHow much can the elderly increase their strength with a proper resistance-training program?

Aging and Joint FlexibilityDescribe the change in joint flexibility with aging.


Endocrine Changes With AgingList three “hormonal systems” most affected by aging.

1. 3.

2.

Aging and Nervous System FunctionDescribe the general effect of aging on the nervous system.

Aging and Pulmonary FunctionDescribe how aging affects pulmonary function.

Aging and Cardiovascular FunctionMaximal Oxygen UptakeGive the estimated maximum heart rate for a 59-year old person. Show your calculations.

List two reasons that VO2max declines with age.1. 2.

A System Responsive to Training at Any AgeHow much can a middle age person expect to increase VO2max with proper training?

Other Age-Related VariablesGive three reasons for age-related decrements in HRmax.

1. 3.

2.

Aging and Body CompositionHow much weight does the average 20-year old male gain by age 60?


Regular Exercise: A Fountain Of Youth?List five health benefits of regular physical activity.

1. 4.

2. 5.

3.

Enhanced Quality to a Longer Life: A Study of Harvard AlumniDescribe major findings of the study of Harvard Alumni.

Coronary Heart DiseaseWhat percentage of total deaths do diseases of the heart and blood vessels cause?

A Life-Long ProcessAt what age can fatty streaks develop in the coronary arteries?

Women at Risk

Write four statements that summarize the heart disease risk for females emphasizing unique sex differences in risk factors.

1. 3.

2. 4.

Risk Factors for Coronary Heart DiseaseList the major modifiable and fixed coronary heart disease risk factors.

Modifiable risk factors

Fixed risk factors

Age, Sex, and HeredityWhy do women possess a “gender advantage” for avoiding heart disease?


Blood Lipid AbnormalitiesCholesterol and TriglyceridesList desirable cholesterol and triglyceride levels for adults.

Cholesterol

Triglyceride

Importance of Cholesterol Forms

List four different lipoproteins.1. 3.

2. 4.

Physical ActivityHow much greater is heart disease risk for a sedentary compared to a physically active person?

HypertensionIndicate the lower borderline limit for the classification of high blood pressure.

Systolic

Diastolic

Cigarette SmokingList three facts about cigarette smoking and the risk of developing CHD.

1. 3.

2.

ObesityDiscuss how obesity contributes as a multiple CHD risk factor.


Personality and Behavior PatternsDescribe personality characteristics of individuals who exhibit Type A and Type B behavior.

Type A

Type B


PRACTICE QUIZ1. The difference between physical

fitness and physical activity:a. nothingb. has to do with amount of activity

performedc. has to do with absence of diseased. has to do with length of lifee. none of the above

2. The oldest old:a. age 85 and olderb. age 70 and olderc. age 100 and olderd. cannot exercisee. none of the above

3. Physiology measures:a. decline with age, but not at the

same rateb. decline with age at the same ratec. start to decline after age 15 yd. stop declining for the oldest olde. none of the above

4. Harvard alumni study:a. concerned with quality and

quantity of life as affected by exercise habits

b. showed that vigorous exercise was necessary for longevity

c. showed that nutrition was more important than exercise in predicting longevity

d. showed that football players die young

e. none of the above5. CHD

a. coronary heart diseaseb. child health diseasesc. comorbidity, health, deathd. relates to exercise training

techniquese. none of the above

6. Hyperlipidemia:a. elevated HDL and LDLb. relates to disease of pancreasc. controlled with high protein dietd. elevated blood lipidse. none of he above

7. HDL, LDL, VLDL:a. lipoproteinsb. vitaminsc. proteinsd. enzymese. none of the above

8. HDL:Cholesterol ratio:a. greater than 4.5 indicates high

risk of heart diseaseb. less than 4.5 indicates high risk

heart diseasec. not important as a heart disease

riskd. chronic exercise decreasese. none of the above

9. True or False: Physical activity can be thought of as an independent heart disease risk factor:a. Trueb. False

10. Type A personality:a. calm, easy going, laid backb. increased risk for heart diseasec. usually are olderd. usually do not exercisee. none of the above


LECTURE #11TRAINING MUSCLES TO BECOME STRONGER

IntroductionWeightlifting began as a spectator sport in America in the early 1840s, practiced by

“strongmen” who showcased their prowess in traveling carnivals and sideshows. By the mid-1880s, measuring muscular strength became more commonplace, particularly in schools and colleges as one of several indicators of an individual fitness. In 1897 at a meeting of College Gymnasium Directors, strength test contests were established to determine overall body strength based on measures of back, leg, arm, and chest strength. The first 5 colleges to rank in the 1898–1899 contest were Harvard, Columbia, Amherst, Minnesota, and Dickinson.

By the mid-1900s, physical culture specialists, body builders, competitive weight lifters, field event athletes, and some wrestlers used “weightlifting” exercises. Most other athletes, however, refrained from lifting weights for fear it would slow them and increase muscle size so they would lose joint flexibility and become “muscle-bound.” Research in the late 1950s and early 1960s silenced this myth by showing that muscle-strengthening exercises did not reduce movement speed or flexibility. In longitudinal experiments with untrained healthy subjects, heavy-resistance exercises actually increased speed and power.

In this lecture I explore the underlying rationale of strength (resistance) training, including physiologic adjustments as muscles become stronger with training. The discussion centers on how to measure muscle strength, strength differences between men and women, and different resistance training regimens.

Objectives Describe the following four methods to assess muscular strength: (a) cable tensiometry,

(b) dynamometry, (c) one-repetition maximum, and (d) computer-assisted isokinetic dynamometry.

Compare absolute and relative upper and lower body muscular strength in men and women.

Define concentric, eccentric, and isometric muscle actions, including examples of each. Provide general recommendations for appropriate frequency, overload, and sets and

repetitions for dynamic exercise resistance training. Explain specificity of training response for muscular strength related to enhanced sports

performance. Describe how psychological and muscular factors influence maximum strength capacity. Describe delayed-onset muscle soreness (DOMS).


Foundations For Studying Muscular StrengthThe scientific foundations for incorporating strength training as part of an athlete’s

competitive training can be traced to the Chinese in 3600 BC. In the Chou dynasty (1122-249 BC), conscripts had to pass weight-lifting tests before they became soldiers. Weight training also took place in ancient Egypt and India; sculptures and illustrations depict athletes training with heavy stone weights. Women also practiced weight training; wall mosaics recovered from Roman villas showed young girls exercising with hand-held weights. During the “Age of Strength” in the sixth century, weight lifting competitions often took place between soldiers and athletes. Galen, the famous early Greek physician (Lecture 2), refers to exercising with weights (halters) in his various writings.

The quest to develop muscular strength led to different “systems” of resistance training. The first “modern” text detailing a strength training system appears to be the 1561 text by Sir Thomas Elyot, “The Boke Named The Govuenour” (Elyot’s treatise establishes a detailed curriculum of study, including intellectual and artistic pursuits and physical education, about the role of gymnastics and strength development standards to which a governor should aspire). In the 1860s, Archibald MacLaren, a Scotsman, compiled the first system of physical training with dumbbells and barbells for the British army.

Objectives of Resistance TrainingThe study of strength development provides practical applications in six areas: Weight

lifting and power lifting competition1. Body building (for aesthetic goals2. Fitness and health enhancement3. Physical therapy; rehabilitation from injury4. Sport-specific resistance training5. Understanding muscle function and structure6. Definition of Terms in Resistance Training

Terms and jargon abound in the area of resistance training, yet certain terms consistently appear in the research literature. Below is listed a selection of common resistance training terms.

Cheating. Breaking from strict form (e.g., rather than maintaining an erect upper body when performing a standing arm curl, a slight body swing at the start the movement allows the person to lift a heavier weight (or the same weight more times). Cheating increases injury if performed improperly.

Circuit Resistance Training (CRT). Series of resistance training exercises performed in sequence with minimal rest between exercises. More frequent repetitions with less resistance activate the cardiovascular system to produce an aerobic training effect.

Concentric Action. Muscle shortening during force applicationDynamic Constant External Resistance (DCER). Training: Resistance training where

external resistance or weight does not change; joint flexion and extension occurs with each repetition. Formerly (but incorrectly) referred to as “isotonic” exercise.

Eccentric Action. Muscle lengthening during force application.Exercise Intensity. Muscle force expressed as a percentage of muscle’s maximum force-

generating capacity or some level of maximum.Isokinetic Action. Muscle action performed at constant angular limb velocity.Isometric Action. Muscle action without change in muscle length.

Figure 1. Measurement of static strength by (A) cable tensiometer, (B) hand-grip dynamometer, and (C) back-leg lift dynamometer.


Maximal Voluntary Muscle Action (MVMA). Maximal force generated in one repetition (1-RM), or performing a series of submaximal actions to momentary failure.

Muscular Endurance. Sustaining maximum (or submaximum) force; often determined by assessing maximum number of exercise repetitions at a percentage of maximum strength.

Overload. A muscle acting against a resistance normally not encountered (unaccustomed stress).

Periodization. Variation in training volume and intensity over a specified time period; goal to prevent staleness and peak physiologically for competition.

Plyometrics. Resistance training involving eccentric-to-concentric actions performed quickly so a muscle stretches slightly prior to the concentric action; utilizes stretch reflex to augment muscle’s force-generating capacity.

Power. Rate of performing work (Force x Distance ÷ Time, or Force x Velocity). Power applied to weightlifting relates to mass lifted times vertical distance it moves, divided by the time to complete the movement; if 100 lbs moves vertically 3 feet in one second, the power generated = 100 lb x 3 ft ÷ 1 s or 300 ft-lb•s-1.

Progressive Overload. Incrementally increasing the stress placed on a muscle as it produces greater force or greater endurance.

Range of Motion (ROM). Maximum movement through an arc of a body joint.Repetition. One complete exercise movement, usually consisting of concentric and

eccentric muscle actions or one complete isometric muscle action.Repetition Maximum (RM). Greatest force generated for one repetition of a movement

(1-RM).Set. Pre-established number of repetitions performed.Sticking Point. Region in an exercise movement (against a set resistance) that provides

greatest difficulty completing the movement.Strength. Maximum force-generating capacity of a muscle or group of muscles.Torque. Force that produces a turning, twisting, or rotary movement in any plane about an

axis (e.g., movement of bones about a joint); commonly expressed in Newton-meters (Nm).Training Volume. Total work performed in a single session.

Variable Resistance Training. Training with equipment that uses a lever arm, cam, or pulley to alter the resistance to match increases and decreases in muscle force capacity throughout a joint’s ROM.

Measurement of Muscular Strength

Four methods generally assess muscular strength, i.e., the maximum force, tension, or torque generated by a muscle or muscle groups: Cable tensiometry, dynamometry, one-


repetition maximum, and computer assisted electromechanical and isokinetic determinations.

Cable TensiometryFigure 1A shows a cable tensiometer measuring muscular force during knee extension.

Increased force on the cable depresses a riser over which the cable passes; this deflects the pointer and indicates the subject’s strength score. The application of the tensiometer for strength measurements differs considerably from its original use for measuring tension on steel cables linking various parts of an airplane.

Cable tensiometry provides an excellent way to isolate a muscle at a specific joint angle for strength determinations before and after training and rehabilitation. This method for strength assessment provides another advantage because it can be applied in different movement phases to give a clear picture of the strength (or weakness) of particular muscles acting in a range of motion (ROM). This cannot be done easily with standard weight-lifting tests.

DynamometryFigures 1B and C display handgrip and back-lift dynamometers to assess static strength.

Both devices operate on the principle of compression. Application of external force to the dynamometer compresses a steel spring and moves a pointer. By knowing how much force must move the pointer a given distance, one can determine how much external “static” force has been applied to the dynamometer.

One-Repetition MaximumThe one-repetition maximum (1-RM) technique serves as a dynamic method for

measuring muscular strength. To test 1-RM for single or multiple muscle groups, the initial weight should be close to but below maximum lifting capacity. Depending on the muscle group, increments in weight lifted range from 1 to 5 kg. The 1-RM maneuver requires concentric and eccentric muscle actions, but only the concentric phase of the action evaluates 1-RM.

Computer-Assisted Electromechanical and Isokinetic DeterminationsMicroprocessor technology integrated with exercise equipment provides a unique way to

quantify muscular force during a variety of movements. Modern instrumentation measures force, acceleration, and velocity of body segments in various movement patterns. Force platforms can measure the external application of muscular force by limbs during jumping. Other electromechanical devices measure forces generated during all movement phases of cycling, rowing, supine bench press, seated and upright leg press, and exercises for other trunk, arm, and leg movements weight an individual can bench press or squat.

Strength Testing ConsiderationsThe following factors affect strength testing, regardless of assessment method. It is

necessary to: Give standardized instructions. Allow a warm-up of uniform duration (e.g., 3 to 5 minutes) and intensity (e.g., 50% of

previously established 1-RM depending on muscle group). Provide adequate practice several days before testing to minimize a “learning” component

that could compromise initial results or inflate evaluation of true training effects. Ensure constancy of limb position and/or measurement angle. Provide several trials (repetitions) to establish a criterion score.


Administer strength tests with established reliability (reproducibility) of scores. Consider individual differences in body size and composition when evaluating strength

scores among individuals and groups.

Physical Testing in the Occupational SettingNo one “best” measure of muscular strength exists. Each individual possesses an array of

muscular “strengths” and “powers.” Often, these expressions of physiologic function and performance are not co-related to each other. Likewise, a person has diverse capabilities for expressing aerobic capacity, depending on the muscle mass exercised. In the occupational setting, a 12-minute run to infer aerobic capacity for fire fighting or lumbering (both requiring significant upper body aerobic function), or static grip or leg strength to evaluate the diverse strengths and powers required in such occupations, would be physiologically unwise in light of current knowledge of performance specificity. Measurement in the occupational setting requires attention not only to faithfully replicating specific job tasks, but also measuring the physiological demands of the work for intensity, duration, and pace.

Important Issues for Training Muscles to Become StrongerTraining muscles to become stronger requires different principles and adherence to specific

guidelines.

Overload and IntensityMuscular strength training requires application of the overload principle by use of

weights (dumbbells or barbells), immovable bars, straps, pulleys, or springs, and oil, air, and water hydraulic devices. In each case, the muscle responds to the intensity of the overload rather than to the actual form of overload.

The amount of overload is usually expressed as a percent of the maximum force-generating capacity (1-RM) of a non-fatigued muscle or muscle group. Performing a voluntary maximal muscle action means the muscle must move against as much resistance as its present capacity level allows. Although a partially fatigued muscle cannot generate the same force as a non-fatigued muscle, the last repetition in a set to momentary failure still represents a voluntary maximal muscle action. Muscular overload in resistance training usually requires voluntary maximal muscle actions.

Three approaches (either singularly or in combination) apply muscular overload in resistance training:

1. Increase load or resistance2. Increase number of repetitions3. Increase speed of muscle action

Figure 2. Muscular force during (A) concentric (shortening), (B) eccentric (lengthening), and (C) isometric (static) actions.


Muscular overload, referred to as training intensity, represents the most important concept in strength development; it relates to the necessity for training above a

minimum threshold level to induce a training response. Minimal intensity for overload occurs between 60 to 70% of 1-RM. This means that performing a large number of repetitions with a light resistance generally produces minimal strength gains.

Muscle ActionsConcentric action represents the most common form of muscle action; it occurs in dynamic activities where the muscle shortens and joint movement occurs as tension develops. Figure 2A illustrates a concentric muscular action by raising a dumbbell from the extended to flexed elbow position. Because a concentric muscle action produces actual muscle shortening, the word

“contraction” frequently describes this process.Eccentric action (also called lengthening, stretching, or plyometric) occurs when external

resistance exceeds muscle force, and the muscle lengthens while developing tension. Figure 2B shows a weight slowly lowered against the force of gravity. The muscles of the upper arm increase in length as they provide braking action to prevent the weight from crashing to the floor.

Isometric action (also called static or stationary) occurs when a muscle attempts to shorten but cannot overcome the resistance. Considerable muscular force can be generated during an isometric action with no noticeable muscle lengthening or shortening or joint movement. Figure 2C illustrates an isometric muscular action.

The term isotonic commonly describes concentric and eccentric muscle actions because movement occurs in both cases. The term isotonic comes from the Greek isotonos (iso meaning the same or equal; tonos, tension or strain.) Actually this term should not be applied to most dynamic muscle actions that involve movement because the muscle’s force-generating capacity varies as the joint angle changes; thus, force output does not remain constant through the ROM. Dynamic constant external resistance (DCER) provides a more useful term for strength (resistance) training in which external resistance or weight does not change, but lifting (concentric) and lowering (eccentric) phases occur during each repetition. DCER implies that the external weight or resistance remains constant throughout the movement.

Figure 3. Maximum force-velocity relationship for shortening and lengthening muscle actions. Rapid shortening velocities generate the least maximum force. Shortening velocity becomes zero (maximum isometric force) when the curve crosses the y-axis.


Force:Velocity RelationshipDifferent physical activities require different amounts of strength (force) and power.

Absolute or peak force generated in a movement depends upon the speed of muscle lengthening and shortening. Figure 3 shows the force:velocity relationship for concentric and eccentric actions. Muscles shorten at different velocities (horizontal axis of graph) depending on the load placed on them. As the load increases, maximum velocity decreases. Conversely, a muscle’s force-generating capacity (vertical axis of graph) rapidly declines with increased shortening velocity. This explains the difficulty in attempting to move a heavy weight rapidly.

A concentric action becomes a lengthening (eccentric) action when the external load exceeds a muscle’s maximum force capacity (noted as point 0 on the vertical axis.) Rapid eccentric actions generate the greatest muscular force. This may explain muscle damage and delayed muscle soreness while doing eccentric exercise. Force at zero velocity shortening (isometric action) exceeds all forces generated with concentric actions. Muscle fiber type also influences the force-velocity relationships; fast-twitch muscle fibers produce greater muscle force at fast movement speeds than slow-twitch fibers.

Power-Velocity Relationship

Figure 4 (next page) shows an “inverted U”

relationship between a muscle’s maximal power output and its speed of limb movement. Peak power rapidly increases with increasing velocity to a peak velocity region. Thereafter, maximal power output decreases because of the significant reduction in maximum force at faster movement speeds (Figure 15-4.) Thus, each muscle group has an optimum movement speed to produce maximum power. At any movement velocity, greater peak power occurs in fast-contracting fibers than slow-contracting fibers due mainly to the biochemical differences between fibers.

Figure 4. Power-velocity relationship. Power (work per unit time) increases as a function of movement velocity to a peak velocity region.


Load:Repetition Relationship

The total work accomplished by muscle action depends on the load (resistance) placed on the muscle. One can perform high repetitions with light loads, but few repetitions with near maximal loads.

Sex Differences In Muscular Strength

Two approaches can determine whether true sex differences exist in muscular strength.Absolute basis (as total force exerted)Relative basis (as force exerted in relation to body mass, fat-free body mass, or muscle cross-sectional area)

Absolute StrengthWhen comparing absolute

strength (total force in pounds or kilograms), men achieve considerably higher strength scores than women for all

muscle groups, regardless of test mode. Sex differences in strength are particularly apparent for upper body strength evaluations; women exhibit about 50% less strength than men. In lower body strength, women achieve 20 to 30% below the scores of male counterparts. Exceptions usually include strength-trained female track and field athletes and bodybuilders who train diligently with overload resistance exercise to significantly increase the strength of specific muscle groups.

Relative StrengthHuman skeletal muscle in vitro generates 16 to 30 Newton’s (N) maximum force per square

centimeter of muscle cross-sectional area (MCSA) regardless of sex. In the body (in vivo), force-output capacity varies depending on the arrangement of bony levers and muscle architecture.

Individuals with the largest MCSA generate the greatest muscular force. The strong, linear relationship between strength and muscle size (r = 0.95) indicates little difference in arm flexor strength for the same size muscle in men and women.

RESISTANCE TRAINING FOR CHILDRENWhile resistance training for children has gained in popularity, its benefits and possible

risks remain relatively unknown. Because skeletal development is not complete in young children and adolescents, obvious concern arises about the potential for bone and joint injury with heavy muscular overload. Furthermore, one might question whether resistance training can induce significant strength improvements at a relatively young age because the hormonal


profile continues its progressive development (particularly for the tissue-building hormone testosterone). Limited evidence indicates that closely supervised resistance training programs using concentric-only muscle actions with high repetitions and low resistance significantly improve children’s muscular strength with no adverse effect on bone or muscle.

The following guidelines should be used regarding strength training with children.

Age Strength Training Guidelines

5-7

8-10

11-13

14-15

16+

Introduce child to basic exercises with little or no weight; develop the concept of a training session; teach exercise techniques; progress from body weight calisthenics, partner exercises, and lightly resisted exercises; keep volume low.Gradually increase the number of exercises; practice exercises technique for all lifts; start gradual progressive loading of exercises; keep exercises simple; increase volume slowly; carefully monitor tolerance to exercise stress.Teach all basic exercise techniques; continue progressive loading of each exercise; emphasize exercise technique; introduce more advanced exercises with little or no resistance.Progress to more advanced resistance programs; add sport-specific components; emphasize exercise techniques; increase volume.Entry level into adult programs after all background experience has been gained

Systems of Resistance TrainingFive fundamentally different but interrelated systems of training result in muscular strength

development: 1. Isometric training2. Dynamic constant external resistance training 3. Variable resistance training4. Isokinetic training5. Plyometric training

Isometric Training (Static Exercise)Isometric strength training gained popularity between 1955 and 1965. Research in

Germany during this time showed an increase in isometric strength of about 5% a week from only a daily, single, two-thirds maximum isometric action for six-seconds duration! Repeating this action five to 10 times produced greater increases in isometric strength. Gains in strength from this simple exercise overload seemed beyond belief, and subsequent research demonstrated that isometric strength gains progressed at a much slower rate. Research also showed that gains in strength from isometrics related to repetitions, duration of muscle action, and training frequency.

Research since 1965 has revealed the following information regarding isometric training: Maximal voluntary isometric actions (100% maximum) produce greater gains in

isometric strength than submaximal isometric actions.


Duration of muscle activation directly relates to increases in isometric strength. One daily isometric action does not increase isometric strength as effectively as

repeated actions. An optimal isometric training program consists of daily repeated isometric actions. Isometric training does not provide a consistent stimulus for muscular hypertrophy. Gains in isometric strength occur predominantly at the joint angle used in training.

A drawback to isometric training is difficulty in monitoring training results. Because essentially no movement occurs, it is difficult to determine objectively if the person’s strength actually improves and whether he or she applies an appropriate overload force during training. Isometric force measurement requires specialized equipment (e.g., strain gauge or cable tensiometer) not readily available at most exercise facilities.

Dynamic Constant External Resistance (DCER) TrainingThis popular system of resistance training involves lifting (concentric) and lowering

(eccentric) phases with each repetition using weight plates (barbells and dumbbells) or exercise machines that feature different applications of muscle overload.

Progressive Resistance ExerciseResearchers in rehabilitation medicine following World War II devised a method of

resistance training to improve the force-generating capacity of previously injured limbs. Their method involved three sets of exercise, each consisting of 10 repetitions done consecutively without rest. The first set involved one-half the maximum weight lifted 10 times or one-half 10-RM; and the second set used three-quarters 10-RM; the final set required maximum weight for 10 repetitions or 10-RM. As patients trained and became stronger, 10-RM resistance increased periodically to match strength improvements. This technique of progressive resistance exercise (PRE) , a practical application of the overload principle, forms the basis for most strength conditioning programs.

Variations of PREVariations of PRE have determined an optimal number of sets and repetitions, including

frequency and relative intensity of training, to improve strength. The findings can be summarized as follows:

Performing between 3-RM and 9-RM is the most effective number of repetitions to increase muscular strength.

PRE training once weekly with only 1-RM for one set increases strength significantly after the first week of training, and each week up to at least the sixth week.

No particular sequence of PRE training with different percentages of 10-RM produces more effective strength improvement, provided each training session consists of one set of 10-RM.

Smaller strength increases occur when performing one set of an exercise rather than two or three sets, and three sets produces greater improvement than two sets.

For beginners, significant strength increases occur with only one training day weekly, but the optimum number of training days per week with PRE remains unknown.

When PRE training uses several different exercises, training four or five days a week may be less effective for increasing strength than training two or three times weekly. More frequent training may prevent sufficient recuperation between exercise sessions, which could retard neuromuscular adaptation and strength development.

A fast rate of movement for a given resistance generates greater strength improvement than lifting at a slower rate. Neither free weights nor concentric-eccentric-type weight


machines or “isotonic” devices produce inherently superior results compared with other strength development methods.

Variable Resistance TrainingA limitation of typical DCER weight-lifting exercise is failure of muscles to generate

maximum force through all phases of the movement. Variable resistance training equipment alters resistance to movement by use of a lever arm, irregularly shaped metal cam, or pulley to match increases and decreases in force in relation to joint angle (lever characteristics) throughout a ROM. This adjustment facilitates strength gains allowing near-maximal force production throughout a ROM.

Research has shown that a single cam cannot possibly compensate fully for individual differences in mechanics and force applications at all phases of the particular movement. Variations in limb length, point of attachment of muscle tendons to bone, body size, and strength at different joint angles all affect maximum force generated throughout a ROM. In most cases, cams produce too much resistance during the first half and too little resistance during the second half of flexion and extension exercises. Despite these limitations, cam devices produce strength improvements comparable to other types of equipment.

Isokinetic TrainingIsokinetic resistance training differs from isometric and DCER methods; it employs a

muscle action performed at constant angular limb velocity. Unlike dynamic resistance exercise, isokinetic exercise does not require a specified initial resistance; rather, the isokinetic device controls movement velocity. The resisting force offered by the isokinetic machine cannot be accelerated; any force applied against the device’s lever results in an opposing force, which thwarts any increase in movement velocity. The muscles exert maximal force throughout the ROM while shortening (concentric action) at a specific velocity. Advocates of isokinetic training argue that ability to exert maximal force throughout the full ROM optimizes strength development. Also, concentric-only actions minimize muscle and joint injury and resulting pain.

Plyometric TrainingAthletes who require specific powerful movements (e.g., football, volleyball, sprinting, and

basketball) perform exercise training termed plyometrics. With plyometric training, movements make use of the inherent stretch-recoil characteristics of skeletal muscle and neurological modulation via the stretch or myotatic reflex. Consider walking: When the foot first hits the ground, the quadriceps initially act (stretch) eccentrically, then briefly isometrically, before the shortening phase of a muscle’s action begins. The term stretch-shortening cycle describes the sequence of sequentially linked eccentric-isometric-concentric muscle actions. When stretching occurs rapidly, stored elastic energy in muscle fibers and initiation of the myotatic reflex combine to produce a powerful concentric action.

Vertical jumping provides an example of the stretch-shortening cycle to enhance performance. During a normal vertical jump, the jumper bends at the knees and hips (eccentric action of extensors), pauses briefly (isometric action), and rapidly reverses direction (concentric action) to jump upward as high as possible. If this same movement stops for several seconds following the knee bend (just before reversing movement direction), the subsequent jump (concentric action) produces a lower jump height compared with a performance that uses the complete stretch-shortening cycle.


Figure 6. Examples of stretch-shortening cycle (plyometric) exercises. A, strength development; B, depth jumping; C, reactive ability.


Practical ApplicationsA plyometric training drill incorporates one’s body mass and the force of gravity to provide

the all-important rapid prestretch, or “cocking” phase to “activate” the stretch reflex and the muscle’s natural elastic recoil elements. Lower-body plyometric drills include a standing jump, multiple jumps, repetitive jumping in place, depth or drop jumps (from 1 to 4-ft. heights), and various modifications of single and double leg jumps. Repeating these exercises regularly supposedly provides both neurological and muscular training to enhance power performance of specific muscles. Figure 6 shows examples of plyometric exercises for strength development, using resistance and other apparatus, including general jumping exercises and depth jumps.

Comparison of Training SystemsFew research studies directly compare different training systems within the same

experimental protocol. Some studies compare two different training systems (e.g., isometric versus variable resistance; isometric versus isokinetic; isometric versus eccentric). The results generally support the specificity and individual differences principles. When training and testing incorporate the same system, relatively large strength increases occur, regardless of type of training system. When testing uses a different system than in training, smaller training-induced strength increases occur, and in some experiments become nonexistent. Difficulties arise in trying to compare different training systems because of methodological problems equating training volume (sets and repetitions), total work, total training time, and most importantly, training intensity. This makes it almost impossible to directly “prove” one strength training system “better” than another. Moreover, some individuals simply respond more favorably to one system and not another.

PeriodizationPeriodization refers to organizing resistance training into phases of different types of

exercise done at varying intensities and volumes for a specific time period. Figure 7 displays a wave-like, basic periodization scheme (and descriptions) with four phases or mesocycles . This system shows that phase one consists of high volume (repetitions and sets) and low intensity exercise. During the next three phases, total exercise volume decreases, and intensity increases. Periodization cycles can vary from one cycle to two or three cycles yearly. In

Figure 7. Basic periodization scheme comprising four transition phases. The periodization concept subdivides a macrocycle into distinct phases or mesocycles. These in turn usually separate into weekly microcycles.

Mesocycle 4


general, each of the four phases emphasize a different component of strength development over a competitive season.

Adaptations To Resistance TrainingResistance training produces acute responses and chronic adaptations. An acute

response refers to immediate changes (in muscle or other cells, tissues, or systems) that occur during or immediately after a single bout of resistance exercise. For example, enzyme levels and energy stores change in response to specific muscle actions. Chronic changes take place

with repeated stimuli over the course of a training regimen. Adaptation refers to how the body adjusts to repeated stimuli. The body responds acutely to a given stress, while repeated exposure to the stimulus produces long-lasting changes that affect the acute response over time (e.g., less disruption in cellular integrity [muscle damage] with a given level of exercise.)

Knowing the acute and chronic responses to resistance training facilitates exercise prescription and program design. Adaptations to repeated muscular overload ultimately determine a training program’s effectiveness. The time-course of adaptations varies among individuals and depends on the nature and magnitude of prior adaptations. A resistance-training program should consider the expression of individual differences in adaptation (training responsiveness.)

Adaptations to resistance training occur in diverse body systems from the cellular to systemic level. Figure 8 displays six factors that impact development and maintenance of muscle mass. Unmistakably, genetics provides the governing frame of reference that influences the effect of each other factor on the ultimate training outcome. Muscular activity, however, contributes little to tissue growth without appropriate nutrition to provide essential building blocks. Similarly, training outcome depends on specific hormones and patterns of nervous system activation. Without overload, each of the other factors remains relatively ineffective for inducing strength development.

Fast- and Slow-Twitch Muscle FibersExercise physiologists have applied invasive biopsy techniques to study the functional and

structural characteristics of human skeletal muscle. The biopsy procedure uses a special needle to puncture the muscle and obtain approximately 20 to 40 mg of tissue (the size of a

Figure 8. Six factors that impact the development and maintenance of muscle mass.


grain of rice) for chemical and microscopic analysis. Two distinct types of fiber have been identified in human skeletal muscle: fast-twitch and slow-twitch. The proportion of each fiber type within a particular muscle probably remains fairly constant throughout life.

Fast-Twitch FiberFast-twitch muscle fiber, also known as type II fiber, possesses a high capacity for

anaerobic ATP production during glycolysis. These fibers possess a rapid contraction speed; they become activated in sprint activities that depend almost entirely on anaerobic metabolism for energy. The metabolic capabilities of fast-twitch fibers also become important in stop-and-go or change-off-pace sports like basketball, soccer, lacrosse, and field hockey These sports often require rapid energy transfer through anaerobic metabolism.

Slow-Twitch FiberThe slow-twitch or type I muscle fiber has a contraction speed about one-half as fast as its

fast-twitch counterpart. Slow-twitch fibers possess numerous mitochondria and a high concentration of enzymes required to sustain aerobic metabolism. They demonstrate a much greater capacity to generate ATP aerobically than their fast-twitch counterparts. As such, slow-twitch muscle fiber activation predominates in endurance activities that depend almost exclusively on aerobic metabolism. Middle-distance running or swimming, or basketball, field hockey, and soccer, require a blend of both aerobic and anaerobic capacities. Both types of muscle fibers become activated in such sports.

From the preceding discussion, do you think that the predominant fiber type in specific muscles contributes to success in a particular sport or activity?

Muscle AdaptationsPsychologic inhibitions and learning factors greatly modify muscular strength, but anatomic

and physiologic factors within the muscle determine the ultimate limit of strength development. The gross and ultrastructural changes in muscle with chronic resistance training generally produce adaptations in the contractile apparatus, accompanied by substantial gains in muscular strength and power. An increase in the muscle’s external size represents the most visible adaptation to resistance training. Muscle fiber hypertrophy (increase in size of individual fibers) usually explains increases in gross muscle size, although increased fiber number (fiber hyperplasia) provides a hotly debated alternative hypothesis.

Muscle Fiber HypertrophyIncreases in muscle size (hypertrophy) with resistance training for men and women can be

viewed as a fundamental biologic adaptation. Weightlifters’ and body builders’ extraordinarily large muscle size and definition results from enlargement of individual muscle cells, mainly fast-twitch fibers. Growth takes place from one or more of the following adaptations:

Increased contractile proteins (actin and myosin) Increased number and size of myofibrils per muscle fiber Increased amounts of connective, tendinous, and ligamentous tissues Increased enzymes and stored nutrientsNot all muscle fibers undergo the same degree of enlargement with resistance training.

Muscle growth depends on the muscle fiber type activated and recruitment pattern. With initiation of heavy resistance exercise training, alterations in various muscle proteins begin within several workouts. As training continues, contractile proteins increase in conjunction with enlargement of muscle fiber cross-sectional area.


Muscle Remodeling: Can Fiber Type Be Changed?Fourteen men performed three sets of 6-RM leg squats three times per week to evaluate the

effects of eight weeks of resistance training on muscle fiber size and composition in leg extensor muscles. Biopsies from the vastus lateralis before and after training showed significant increases in the volume of fast-twitch fibers. However, no change resulted in the percentage distribution of fast- and slow-twitch muscle fibers. This finding supported previous short-term studies of overload training and muscle fiber type. Several months of resistance training in adults does not alter basic fiber composition of skeletal muscle. It remains unknown whether specific training early in life, or prolonged training such as engaged in by Olympic-caliber athletes, actually changes a muscle fiber’s inherent twitch (speed of shortening) characteristics. Current consensus maintains that genetic factors determine an individual’s predominant muscle fiber distribution. Significant muscle fiber type transformation (i.e., transforming Type I to Type II fibers) probably does not occur in healthy individuals.

Muscle Hypertrophy and Testosterone LevelsIt is a popular belief that the male sex hormone testosterone facilitates muscle hypertrophy

with resistance training. Testosterone, the chief male hormone, binds with special receptor sites on muscle and other tissues to contribute to male secondary sex characteristics. These include sex differences in muscle mass and strength that develop at puberty’s onset. Variation in testosterone level would then explain individual differences in muscular enlargement with resistance training, and the alleged smaller hypertrophic response of women to muscular overload. Research to date, however, does not support such notions. Essentially no correlation exists between plasma testosterone levels and body composition and muscular strength in men and women.

Muscle Hypertrophy: Male Versus FemaleComputed topography scans to directly evaluate muscle cross-sectional area show that men

and women experience a similar hypertrophic response to resistance training. Men achieve a greater absolute change in muscle size because of a larger initial total muscle mass, but no difference in muscle enlargement on a percentage basis. Other comparisons between elite male and female bodybuilders have verified these observations. The limited data from short-term experiments suggest that women can use conventional resistance training and gain strength and size on a similar percentage basis as men without developing overly large muscles (i.e., absolute change in girth).

Muscle Fiber HyperplasiaDo the actual number of muscle cells increase ( hyperplasia ) with resistance training?

Research in the early 1980s showed that overload training of cat skeletal muscle caused development of new muscle fibers. Hyperplasia occurred through proliferation of satellite cells (cells between the basement layer and plasma membrane of muscle fibers) or longitudinal splitting (a relatively large muscle fiber splits into two or more smaller, individual “daughter” cells.) However, species differences may influence a muscle’s response to overload training; massive cellular hypertrophy in humans with resistance training does not occur in many animal species. Thus, cellular proliferation represents their compensatory adjustment.

Cross-sectional studies of body builders with large limb circumferences and muscle mass failed to show that they possessed significant hypertrophy of individual muscle fibers. While these athletes could have inherited an initially large number of small muscle fibers (which then “hypertrophied” to normal size with training), the findings certainly raise the possibility of significant hyperplasia in humans under certain circumstances. Muscle fibers may adapt differentially to the high-volume, high-intensity training used by body builders compared with the lower-repetition, heavy-load system favored by strength and power athletes. Under most


conditions, hyperplasia does not represent the primary human skeletal muscle adaptation to overload. However, some hyperplasia may occur when Type II fibers reach their upper size limit.

Connective Tissue and Bone AdaptationsSupporting ligaments, tendons, and bone tissues strengthen as muscle strength and size

increase. Changes in ligaments and tendons parallel the rate of muscle adaptation, while bone changes more slowly, perhaps over a six-to-twelve month period. Connective tissue proliferates around individual muscle fibers; this thickens and strengthens the muscles’ connective tissue harness. Such adaptations from resistance training protect joints and muscles from injury and justify resistance exercise for preventive and rehabilitative purposes.

Cardiovascular AdaptationsTraining volume and intensity influence the effect of resistance training on the

cardiovascular system. Subtle yet important differences exist between myocardial enlargement from resistance

training (physiological hypertrophy) and enlargement from chronic hypertension (pathological hypertrophy). In the pathologic condition, ventricular wall thickness increases beyond normal limits regardless of assessment method and evaluative criteria. Dilation and weakening of the left ventricle, a frequent response to chronic hypertension, does not accompany the compensatory increase in myocardial wall thickness with resistance training. The hearts of these athletes usually exceed the size of untrained counterparts, but heart size generally falls within the upper range limits of normal in relation to various measures of body size or cardiac function.

Resistance exercise causes a greater, acute rise in blood pressure than lower-intensity dynamic movements, but does not produce any long-term increase in resting blood pressure. Weight lifters and body builders with hypertension probably have existing essential hypertension, experience chronic overtraining syndrome, use steroids, or possess an undesirable level of body fat or other hypertension risks established for the general population.

Body Composition AdaptationsFor the most part, small decreases occur in body fat, with minimal increases in total body

mass and fat-free body mass. The largest increases amount to about 3 kg (6.6 lb.) over ten weeks, or about 0.3 kg weekly, with results about the same for men and women. Body composition data for other strength training systems show similar results. Thus, no one resistance training system appears superior to another for changing body composition.

Organizing A Resistance Training ProgramIndividuals without prior resistance-training experience generally follow a program

designed to produce all-around strength improvements. Competitive athletes have different needs, and they organize their strength-training regimen into phases with different types of exercises done at varying intensities and volumes. A resistance-training program consists of four aspects:1. Goal setting2. Selecting the appropriate training system3. Determining optimal resistance4. Program organization


Muscle Soreness and StiffnessFollowing an extended layoff from exercise, most of us have experienced pain, aches,

soreness, tenderness, stiffness or an “uncomfortable” feeling in exercised muscles and joints. Temporary soreness can persist several hours immediately following unaccustomed exercise, whereas residual delayed-onset muscle soreness (DOMS) may appear 24-hours later and last up to two weeks, depending on its severity. DOMS can range from mild (24 hours post-exercise) to severe (5 days post-exercise.) Any one of at least six factors may cause DOMS:

Minute tears in muscle tissue damage cells, which release chemical substances (e.g., histamines, prostaglandins, bradykinin, proteolytic enzymes, potassium ions, anaerobic metabolites) that stimulate free nerve endings and produce pain.

Osmotic pressure changes cause fluid retention (swelling) in surrounding tissues. Muscle spasms or cramps (sudden, involuntary, severe contraction in a shortened

position) occur. Overstretching and tearing of portions of the muscle’s connective tissue harness (muscle-

tendon junction) or the muscle’s external surface occur. Structural damage to the internal myofibrils occurs in the region of the Z-line. Damage to this region, called Z-line streaming, may involve mechanical factors induced by high-force eccentric muscle actions.

Alterations in the cell’s mechanism for calcium regulation occur. Inflammation responses (increases in white blood cells and interlukin-1 beta, and

monocyte and leukocyte accumulation) occur.

DOMS and Eccentric Muscle ActionAlthough the precise cause of muscle soreness remains unknown, the degree of discomfort

largely depends on intensity and duration of effort and, most importantly, the type of exercise performed. High-force/high-tension eccentric muscle actions (actively resisting muscle lengthening) generally cause the greatest postexercise discomfort. This effect does not relate to lactate buildup, because level running (primarily concentric actions) produces no residual soreness despite significant elevations in blood lactate. In contrast, downhill running (primarily eccentric actions) causes moderate-to-severe DOMS without significantly elevating lactate during or following exercise.

Cell DamageThe first bout of repetitive, unaccustomed physical activity disrupts the integrity of the

cells’ internal environment. This can produce microlesions and subsequent temporary ultrastructural muscle damage in a pool of stress-susceptible or degenerating muscle fibers. Damage becomes more extensive several days after exercise than in the immediate postexercise period. A single bout of moderate concentric exercise provides a significant prophylactic effect on the development of muscle soreness in subsequent high-force eccentric exercise, with the effect persisting up to six weeks. Such results support the wisdom of initiating a training program with repetitive, moderate concentric exercise to protect against the muscle soreness that occurs following exercise with an eccentric component.

VITAMIN E HELPS REDUCE DOMSVitamin E acts as an important antioxidant to thwart free radical damage via lipid

peroxidation, which increases the vulnerability of the cell and its constituents. A recent study showed that supplements of 800 IU of vitamin E taken every day for seven days before 45 minutes of downhill running minimized muscle damage and reduced inflammation and soreness compared to a control group that received a placebo.


This study demonstrated that heavy resistance exercise increases free radical formation, and that supplementing with vitamin E minimizes damage to muscle fiber membranes. The proposed mechanism remains unknown concerning why intensive resistance exercise increases free radical formation. Research with animals suggests mitochondrial hyperoxia may increase free radical formation during aerobic exercise. For intense muscular activities that emphasize high force production, human research also suggests that reperfusion with blood at the muscle site following exercise may trigger increased free radical formation. Additional research should focus on different modes of high-force exercise, including variations in intensity, duration, and frequency, and vitamin E supplementation on muscle morphology.

Theories Explaining DOMSSeveral theories attempt to explain DOMS, including:

SpasmDue to extreme overload the muscle goes into periodic spasms that result in soreness

TearMinute tears, or ruptures, of individual fibers cause the delayed soreness

Excess metaboliteProlonged exercise that follows a layoff causes metabolite accumulation in muscle; fluid retention occurs because the metabolites trigger osmotic changes in the cellular environment; swelling caused by increased osmotic pressure excites sensory nerve endings and causes pain

Connective tissue damageEccentrically exercised muscles damages connective tissue

Figure 19 outlines probable steps in DOMS development and recuperation.


Figure 9. Proposed sequence for developing DOMS following unaccustomed exercise.



1. Absolute muscular strength

2. Adaptation

3. Circuit resistance training (CRT)

4. Concentric action

5. Delayed-onset muscle soreness (DOMS)

6. Drop-jumping

7. Dynamic constant external resistance (DCER)

8. Dynamometry

9. Eccentric muscle action

10. Force:velocity relationship

11. Isokinetic muscle action

12. Isometric muscle action


13. Muscle hyperplasia

14. Muscular hypertrophy

15. One-repetition maximum

16. Overload principle

17. Periodization

18. Plyometrics

19. Progressive resistance exercise (PRE)

20. ROM

21. Spasm hypothesis

22. Strength training specificity

23. Tear theory

STUDY QUESTIONS

Foundations For Studying Muscular StrengthList four areas for which the study of muscular strength development provides practical applications.


1. 3.

2. 4.

Objectives of Resistance TrainingList three objectives of resistance training for overall fitness and exercise performance.

1. 3.

2.

Measurement of Muscular StrengthList four methods for measuring muscular strength.

1. 3.

2. 4.

Cable TensiometryList one advantages of cable tensiometry testing.

One-Repetition MaximumDefine 1-RM.

Strength Testing ConsiderationsName three factors that affect strength testing.

1. 3.

2.

Important Issues for Training Muscles to Become StrongerOverload and IntensityHow is the amount of overload usually expressed in resistance training?

List three approaches to applying overload in resistance training.


1. 3.

2.

List and describe the three types of muscle action.Action Description

1.

2.

3.

Force-Velocity RelationshipDraw a graph showing the force-velocity relationship for concentric and eccentric actions.

Power-Velocity RelationshipDraw and label a graph showing the relationship between power and velocity.

Force

ShorteningLengthening

Velocity


Sex Differences in Muscular StrengthAbsolute StrengthWhat are the sex differences in absolute muscular strength of the upper and lower body?

Upper Lower

Relative StrengthQuantify the maximum muscle force (N) generated by human skeletal muscle per square cm of muscle cross-sectional area.

Resistance Training For ChildrenList three considerations before initiating a children’s resistance training program.

1. 3.

2.

Systems of Resistance TrainingList five different systems for muscular strength development.

1. 4.

2. 5.

3.

Isometric Training (Static Exercise)List four facts regarding isometric strength training.

1. 3.

2. 4.


Dynamic Constant External Resistance TrainingProgressive Resistance ExerciseBriefly describe the principles of the progressive resistance exercise system.

Variable Resistance TrainingList three factors that why a single variable resistance “cam” does not allow for individual differences in mechanics and force applications.

1. 3.

2.

Isokinetic TrainingExplain in you own words the unique aspects of isokinetic resistance training compared to more “standard” forms of resistance training.

Plyometric TrainingWhat performance would benefit most from plyometric training?

Practical ApplicationsDescribe an example of plyometric training for a track sprint athlete.

Comparison of Training SystemsComparisons of strength training systems generally support the _____________ and ___________________ principles of strength training.

PeriodizationDescribe the purpose of fractionating the resistance training cycle in periodization.

Adaptations to Resistance TrainingDescribe differences between acute and chronic adaptations.


Fast-Twitch FiberList two characteristics of fast-twitch (type II) muscle fibers

1.

2.

What energy system most often supports fast-twitch muscle fiber activity?

Slow-Twitch FiberList two characteristics of slow-twitch or (type I) muscle fibers.

1.

2.

Muscle Fiber HypertrophyList four muscle adaptations that help to explain muscle growth form resistance training.

1. 3.

2. 4.

Muscle Remodeling: Can Fiber Type Be ChangedDescribe changes in the percentages of fast- and slow-twitch fibers resulting from training.

Muscle Hypertrophy: Males Versus FemaleDiscuss whether the skeletal muscle of women can hypertrophy to the same extent as men with regular resistance training.

Muscle Fiber HyperplasiaSummarize the current state of knowledge regarding muscle fiber hyperplasia with resistance training.


Cardiovascular AdaptationsExplain why typical resistance training does not provide an adequate stimulus to improve cardiovascular status.

Cardiovascular AdaptationsWhat happens to blood pressure with resistance training?

Body Composition AdaptationsIs resistance training important for causing changes in body composition?

Muscle Soreness and StiffnessList four possible causative factors for delayed onset muscle soreness.

1. 3.

2. 4.

DOMS and Eccentric Muscle ActionWhy do eccentric actions contribute to greater muscle damage and resulting soreness than concentric actions?

PRACTICE QUIZ1. Isometric action:

a. muscle action without change in muscle length

b. same as eccentric actionc. same as concentric actiond. opposite of eccentric actione. none of the above

2. DCER:a. external resistance does not changeb. external resistance changes by 1-

RMc. same as isometric actiond. same as isokinetic actione. none of the above

3. Dynamometer:a. used to measure isokinetic strengthb. used to measure static strength

c. used to measure range of motiond. same as 1-RMe. none of the above

4. Training intensity:a. same as muscular overloadb. proportional to number of contractions c. inversely proportional to resistanced. same as DCERe. none of the above

5. Concentric action:a. lengthening actionb. same as isokinetic actionc. shortening actiond. involves no joint movemente. none of the above

6. Eccentric action:


a. lengthening actionb. same as isokinetic actionc. shortening actiond. involves no joint movemente. none of he above

7. Power:a. usually expressed in joulesb. force x distance ÷ by timec. distance x time ÷ forced. resistance x distance movede. none of the above

8. PRE:a. same as fartlek trainingb. uses eccentric actions onlyc. uses concentric actions onlyd. uses isometric actions onlye. none of the above

9. True or False: Isokinetic resistance training differs from isometric and DCER methods.a. Trueb. False

10. Muscle hyperplasia:a. increase in muscle cell numberb. increase in muscle cell sizec. increase in size of myofibrilsd. decrease in muscle fiber numbere. none of the above


LECTURE #12BODY COMPOSITION: ASSESSMENT AND HUMAN

VARIATIONSIntroduction

This lecture discusses the gross composition of the human body and present the rationale underlying various direct and indirect methods to partition the body into two basic compartments, body fat and fat-free body mass. It also presents simple, non-invasive methods to analyze an individual’s body composition.

Americans consume more fat per capita than any other nation. They also consume more than 90% of the foods high in saturated fatty acids and processed, high-glycemic carbohydrates. A national preoccupation with food and effortless living causes more than 110 million men and women (and more than 10 to 12 million children and teenagers) to become “over fat” and in need of weight reduction. If these individuals consumed 600 fewer calories daily to reduce to a “normal” body fat level, the annual energy savings would equal the yearly residential electricity demands of Boston, Chicago, San Francisco, and Washington, DC, or the equivalent of more than 1.3 billion gallons of gasoline to fuel about 1 million autos for one year!

Objectives Summarize inadequacies of the “height-weight” tables. Outline characteristics of the “reference man” and “reference woman,” including specific

values for storage fat, essential fat, and sex-specific essential fat. Define fat-free body mass. Define minimal weight. Describe Archimedes’ principle applied to human body volume measurement. Compare the body composition values of average young men and women with elite

competitors in endurance running, wrestling, weight lifting, and bodybuilding. List significant health risks of obesity. Define fat cell hypertrophy and fat cell hyperplasia, and explain how each contributes to

obesity. Outline how “unbalancing” the energy balance equation affects body weight. Explain the

effectiveness of specific exercise for localized fat loss.


Gross Composition of the Human BodyA full understanding of human body composition requires consideration of complex

interrelationships among its chemical, structural, and anatomical components. Figure 1 displays a five-level, multicomponent model for quantifying body composition. Each level of the model becomes progressively more complex as biological organization increases (atoms –––> molecules –––> cells –––> tissue systems –––> whole body.) The model’s essential feature views each level as distinct, with measurable characteristics or subdivisions. This allows the researcher to focus on a particular aspect of body composition related to specific or general biological effect including changes in molecular, cellular, or tissue composition from body weight gain or loss, or diverse forms of exercise training.

Figure 1. Five-level, multicomponent model to assess and interpret body composition. Each component within a level becomes more complex with an increase in the body’s level of biological organization.


Analysis of body composition most often focuses on the tissue and whole body level, primarily because of methodological and practical limitations. Due to marked sex differences in several of the body’s compositional components, a convenient framework for understanding body composition employs the concept of a reference man and reference woman developed by Dr. Behnke (Figure 2.)

Height-Weight TablesHeight-weight tables serve as statistical landmarks to commonly assess the extent of

“overweightness.” They use the average ranges of body mass in relation to stature where men and women aged 25 to 59 years have the lowest mortality rate. Height-weight tables do not consider specific causes of death or quality of health before death. Different versions of the tables recommend different “desirable” weight ranges, with some considering frame-size, age, and sex.

Reference Man and Reference Woman


The reference man is taller by 10.2 cm and heavier by 13.3 kg than the reference woman, his skeleton weighs more (10.4 vs. 6.8 kg), and he possesses a larger muscle mass (31.3 vs. 20.4 kg) and lower total fat content (10.5 vs. 15.3 kg.) These differences exist even when expressing the amount of fat, muscle, and bone as a percentage of body mass. This holds particularly for body fat, which represents 15% of the reference man’s total body mass and 27% for females. The concept of reference standards does not mean that men and women should strive to achieve these body composition values, or that reference values actually represent “average.” Instead, the model provides a useful frame of reference for interpreting statistical comparisons of athletes, individuals involved in physical training programs, and the underweight and obese.

Essential and Storage FatAccording to the reference model, total body fat exists in two storage sites or depots:

essential fat and storage fat.

Figure 2. Body composition of the reference man and reference woman.


Essential FatThe essential fat depot (equivalent to approximately 3% of body mass) consists of fat stored

in the marrow of bones, heart, lungs, liver, spleen, kidneys, intestines, muscles, and lipid-rich tissues of the central nervous system (brain and spinal cord.) Normal physiologic functioning requires this fat. In females, essential fat also includes additional sex-specific essential fat (equivalent to approximately 9% of body mass.) More than likely, this additional fat depot serves biologically important childbearing and other hormone-related functions. Essential body fat likely represents a biologically established limit, beyond which encroachment could impair health status as in prolonged semistarvation from famine, malnutrition, and disordered eating behaviors.

Storage FatIn addition to essential fat depots, storage fat consists of fat accumulation in adipose tissue.

Storage fat includes the visceral fatty tissues that protect the various internal organs within the thoracic and abdominal cavities from trauma, and the larger subcutaneous fat adipose tissue volume deposited beneath the skin's surface. Men and women have similar quantities of storage fat – approximately 12% of body mass in males and 15% in females. For the reference standards, this amounts to 8.4 kg for the reference and 8.5 kg for the reference woman.

Fat-Free Body Mass and Lean Body MassThe terms fat-free body mass and lean body mass refer to specific entities: lean body

mass (a theoretical entity) contains the small percentage of essential fat stores; in contrast, fat-free body mass represents the body mass devoid of all extractable fat. In normally hydrated, healthy male adults, the fat-free body mass and lean body mass differ only in terms of organ-related essential fat. Thus, lean body mass (LBM) calculations include the small quantity of essential fat, whereas fat-free body mass (FFM) computations exclude total body fat (FFM = Body mass – Fat mass.) Many researchers use the terms interchangeably; technically, however, the differences are subtle but real.

Minimal Body MassIn contrast to the lower limit of body mass for the reference man which includes 3%

essential fat, the lower body mass limit for females, termed minimal body mass includes about 12% essential fat (3% essential fat + 9% sex-specific essential fat.) Generally, the leanest women in the population do not have body fat levels below 10 to 12% of body mass, a value that probably represents the lower limit of fatness for most women in good health. The theoretical minimal body mass concept developed by Behnke, incorporating about 12% essential fat, corresponds to a man’s lean body mass with about 3% essential fat. Information from popular magazines and health clubs not withstanding, females cannot achieve the same low body fat content as males. Therefore, women should not expect to “sculpt” their bodies down below 12-17% body fat. Even world-class female body builders, triathletes, and gymnasts rarely have body fat levels below this amount.

Underweight and ThinThe terms underweight and thin are not necessarily synonymous. Measurements in our

laboratories have focused on the structural characteristics of apparently “thin” looking females. Subjects were initially categorized subjectively as appearing thin or “skinny.” Each of the 26 women then underwent a thorough anthropometric evaluation that included skinfolds, circumferences, and bone diameters, and percent body fat and fat-free body mass from hydrostatic weighing.

The results were unexpected because the women’s percent body fat averaged 18.2%, about 7 percentage points below the average 25 to 27% body fat typically reported for young adult


women. Another striking finding included equivalence in four trunk and four extremity bone-diameter measurements among the 26 thin-appearing women, 174 women who averaged 25.6% fat, and 31 women who averaged 31.4% body fat. This meant that appearing thin or skinny did not necessarily correspond to a diminutive frame-size or an excessively low body fat content using lower limits of minimal body mass and essential body fat proposed in Behnke’s model.

Leanness, Exercise, and Menstrual IrregularityPhysically active women in general, and participants in “low weight” or “appearance“ sports

like distance running, body building, figure skating, diving, ballet, and gymnastics, increase their chances of menstrual cycle disturbances. These include delayed onset of menstruation, an irregular menstrual cycle (oligomenorrhea), or complete cessation of menses (amenorrhea.) Amenorrhea in the general population occurs in 2 to 5% of women of reproductive age, whereas it can reach as high as 40% in some sports.

Studies of female ballet dancers support this position; as a group, ballet dancers remain quite lean and have a greater incidence of menstrual dysfunction, eating disorders, and a higher mean age at menarche compared with age-matched, non-dance females. One-third to one-half of female athletes in endurance-type sports probably has some menstrual irregularity. In premenopausal women, irregularity or absence of menstrual function increases their risk of bone loss and musculoskeletal injury when they participate in vigorous exercise.

In some way, the body seems to “sense” high physical stress and inadequate energy reserves to sustain a pregnancy; in such cases, ovulation ceases. Some researchers have argued that at least 17% body fat represents a “critical level” for onset of menstruation and 22% fat as a level required to sustain normal menstruation. They argue that body fat below these levels triggers hormonal and metabolic disturbances that affect the menses.

Leanness Not the Only FactorThe lean-to-fat ratio may play a key role in normal menstrual function (perhaps through

peripheral fat's role in converting androgens to estrogens, or through leptin production in adipose tissue), but so may other factors. Many physically active females fall significantly below the supposed critical level of 17% body fat, but have normal menstrual cycles and maintain a high level of physiologic and performance capacity. Conversely, some amenorrheic athletes have average levels of body fat. In a study from one of our laboratories, we compared menstrual cycle regularity for 30 athletes and 30 nonathletes, all with less than 20% body fat. Four of the athletes and three nonathletes ranging from 11 to 15% body fat had regular cycles, whereas seven athletes and two nonathletes had irregular cycles or were amenorrheic. For the total sample, 14 athletes and 21 nonathletes had regular menstrual cycles. These data corroborate other research, and disprove the hypothesis that normal menstrual function requires a critical body fat level of 17 to 22%.

Potential causes of menstrual dysfunction include the complex interplay of physical, nutritional, genetic, hormonal, regional fat distribution, psychological, and environmental factors. An intense exercise bout triggers the release of an array of hormones, some of which have antireproductive properties. Further research needs to determine whether regular heavy


WHEN A MODEL IS NOT IDEALIn 1967, only an 8% difference existed in body weight between professional fashion models and the average American woman. Today, a model's body weight averages 23% lower than the national average. Twenty years ago, gymnasts weighed about 20 lbs more than present day counterparts. Thus, it comes as no surprise that disordered eating patterns and unrealistic weight goals (and general dissatisfaction with one’s body) remain so common among females of all ages.


exercise produces a cumulative hormonal effect sufficient to disrupt the normal menses. In this regard, when injuries in young amenorrheic ballet dancers prevent them from exercising regularly, normal menstruation resumes, even though body weight remains stable. Additional predisposing factors for reproductive endocrine dysfunction among athletes include nutritional inadequacy and an exercise-induced energy deficit with heavy training.

Based on current research, approximately 13 to 17% body fat should be regarded as an estimate of a minimal body fat level associated with regular menstrual function. The effects and risks of sustained amenorrhea on the reproductive system remain unknown. A gynecologist/endocrinologist should evaluate failure to menstruate or cessation of the normal cycle because it may reflect a significant medical condition (e.g., pituitary or thyroid gland malfunction or premature menopause.) As explained in Lecture 3, prolonged menstrual dysfunction can have profound negative effects on the density of the body's bone mass.

Methods to Assess Body Size and CompositionTwo general approaches determine the fat and fat-free components of the human body:1. Direct measurement by chemical analysis2. Indirect estimation by hydrostatic weighing, simple anthropometric measurements, and

other simple procedures including height and weight

DIRECT ASSESSMENTTwo approaches directly assess body composition. In one technique, a chemical solution

literally dissolves the body into its fat and non-fat (fat-free) components. The other technique requires physical dissection of fat, fat-free adipose tissue, muscle, and bone. Such analyses require extensive time, meticulous attention to detail, and specialized laboratory equipment, and pose ethical questions and legal problems in obtaining cadavers for research purposes.

INDIRECT ASSESSMENTMany indirect procedures assess body composition including Archimedes’ principle (also

known as underwater weighing.) This method computes percent body fat from body density (the ratio of body mass to body volume.) Other procedures use skinfold thickness and girth measurements, x-ray, total body electrical conductivity or impedance, near-infrared interactance, ultrasound, computed tomography, air plethysmography, magnetic resonance imaging, and dual energy x-ray absorptiometry.

Hydrostatic Weighing (Archimedes’ Principle)The Greek mathematician and inventor Archimedes (287-212 BC) discovered a fundamental

principle that is applied to evaluate human body composition. Here is a description of Archimedes’ findinds:

“King Hieron of Syracuse suspected that his pure gold crown had been altered by substitution of silver for gold. The King directed Archimedes to devise a method

for testing the crown for its gold content without dismantling it. Archimedes pondered over this problem for many weeks without succeeding, until one day, he

stepped into a bath filled to the top with water and observed the overflow. He thought about this for a moment, and then, wild with joy, jumped from the bath

and ran naked through the streets of Syracuse shouting, ‘Eureka! Eureka!’ I have discovered a way to solve the mystery of the King’s crown.”

Archimedes reasoned that gold must have a volume in proportion to its mass, and to measure the volume of an irregularly shaped object required submersion in water with collection of the overflow. Archimedes took lumps of gold and silver, each having the same mass as the crown, and submerged each in a container full of water. To his delight, he

Figure 3. Archimedes’ principle to determine the volume and subsequently the specific gravity of the king’s crown.


discovered the crown displaced more water than the lump of gold and less than the lump of silver. This could only mean the crown consisted of both silver and gold as the King suspected.

Essentially, Archimedes evaluated the specific gravity of the crown (i.e., the ratio of the crown's mass to the mass of an equal volume of water) compared with the specific gravities for gold and silver. Archimedes probably also reasoned that an object submerged or floating in water becomes buoyed up by a counterforce equaling the weight of the volume of water it displaces. This buoyant force helps to support an immersed object against the downward pull of gravity. Thus, an object is said to lose weight in water. Because the object’s loss of weight in water equals the weight of the volume of water it displaces, the specific gravity refers to the ratio of the weight of an object in air divided by its loss of weight in water. The loss of weight in water equals the weight in air minus the weight in water.

Specific gravity = Weight in air / Loss of weight in waterIn practical terms, suppose a crown weighed 2.27 kg in air and 0.13 kg less (2.14 kg), when

weighed underwater (Figure 3.) Dividing the weight of the crown (2.27 kg) by its loss of weight in water (0.13 kg) results in a specific gravity of 17.5. Because this ratio differs considerably from the specific gravity of gold (19.3), we too can conclude: “Eureka, the crown must be fraudulent!”

The physical principle Archimedes discovered allows us to apply water submersion or hydrodensitometry to determine the body’s volume. Dividing a person's body mass by body volume yields body density (Density = Mass ÷ Volume), and from this an estimate of percent body fat.

Determining Body DensityFor illustrative purposes, suppose a 50-kg

woman weighs 2 kg when submerged in water. According to Archimedes’ principle, a 48-kg loss of weight in water equals the weight of the displaced water. The volume of water displaced can easily be computed because we know the density of water at any temperature. In the example, 48 kg of water equals 48 L, or 48,000 cm3 (1 g of water = 1 cm3 by volume at 39.2°F.) If the woman were measured at the cold-water temperature of 39.2°F, no density correction for water would be necessary. In practice, researchers use warmer water and apply the density value for water at the particular temperature. The body density of this person, computed as mass / volume, would be 50,000 g (50 kg) / 48,000 cm3, or 1.0417 g•cm-3.

Computing Percent Body Fat, Fat Mass (FM), and Fat-Free Mass (FFM)The equation that incorporates whole body density to estimate the body's fat percentage

derives from the following three premises:Densities of fat mass (all extractable lipid from adipose and other body tissues) and fat-free

mass (remaining lipid-free tissues and chemicals, including water) remain relatively constant

Figure 4. Measuring body volume by underwater weighing.


(fat tissue = 0.90 g•cm-3; fat-free tissue = 1.10 g•cm-3), even with large variations in total body fat and the fat-free mass (FFM) components of bone and muscle.

Densities for the components of the fat-free mass at a body temperature of 37°C remain constant within and among individuals: water, 0.9937 g•cm-3 (73.8% of FFM); mineral, 3.038 g•cm-3 (6.8% of FFM); protein, 1.340 g•cm-3 (19.4% of FFM.)

The person measured differs from the reference body only in fat content (reference body assumed to possess 73.8% water, 19.4% protein, 6.8% mineral.)

The following equation, derived by Berkeley scientist Dr. William Siri, computes percent body fat from estimates of whole body density:

Siri Equation = [Percent body fat = 495 / Body density – 450]The following example incorporates the body density value of

1.0417 g•cm-3 (determined for the woman in the previous example) in the Siri equation to estimate percent body fat:

Percent body fat = 495 / Body density – 450Percent body fat = 495 / 1.0417 – 450

Percent body fat = 25.2%The mass of body fat (FM) can be calculated by multiplying

body mass by percent fat:Fat mass (kg) = Body mass (kg) x [Percent fat ÷ 100]

Fat mass (kg) = 50 kg x 0.252Fat mass (kg) = 12.6

Subtracting mass of fat from body mass yields fat-free body mass (FFM):

FFM (kg) = Body mass (kg) – Fat mass (kg)FFM (kg) = 50 kg – 12.6 kg

FFM (kg) = 37.4In this example, 25.2% or 12.6 kg of the 50 kg body mass

consists of fat, with the remaining 37.4 kg representing the fat-free mass.

Body Volume MeasurementFigure 4 illustrates measurement of body volume by

hydrostatic weighing. First, the subject's body mass in air is accurately assessed, usually to the nearest ±50 g. A diver’s belt secured around the waist prevents less dense (more fat) subjects from floating toward the surface during submersion. Seated with the head out of water, the subject then makes a forced maximal exhalation while lowering the head beneath the water. Using a snorkel and nose clip eases apprehension about submersion in some subjects. The breath is held for several seconds while the underwater weight is recorded. The subject repeats this procedure eight to twelve times to obtain a dependable underwater weight score. Even when achieving a full exhalation, a small volume of air, the residual lung volume, remains in the lungs. The calculation of body volume requires subtraction of the buoyant effect of the residual lung volume, measured immediately before, during, or following the underwater weighing.

Figure 5. Curvilinear relationship between all-cause mortality and body mass index. At extremely low BMIs, the risk for digestive and pulmonary diseases increases, while cardiovascular, gallbladder, and type 2 diabetes risk increases with higher BMIs.


Body Volume Measurement By Air DisplacementTechniques other than hydrodensitometry can measure body volume. For example the BOD

POD, a plethysmographic device for determining body volume. The technology applies the gas law stating that a volume of air compressed under isothermal conditions decreases in proportion to a change in pressure. Essentially, body volume equals the chamber’s reduced air volume when the subject enters the chamber. The subject sits in a structure comprised of two chambers, each of known volume. A molded fiberglass seat forms a common wall separating the front (test) and rear (reference) chambers. A volume-perturbing element (a moving diaphragm) connects the two chambers. Changes in pressure between the two chambers oscillate the diaphragm, which directly reflects any change in chamber volume. The subject makes several breaths into an air circuit to assess thoracic gas volume (which when subtracted from measured body volume yields body volume.) Body density computes as body mass (measured in air) ÷ body volume (measured by BOD POD.) The Siri equation converts body density to percent body fat.

Skinfold MeasurementsSimple anthropometric procedures can successfully predict body fatness. The most common

of these procedures uses skinfolds. The rationale for using skinfolds to estimate total body fat comes from the close relationships among three factors: (a) fat in adipose tissue deposits directly beneath the skin (subcutaneous fat), (b) internal fat, and (c) body density.

Girth MeasurementsGirth measurements offer an easily administered, valid, and attractive alternative to

skinfolds. Apply a linen or plastic measuring tape lightly to the skin surface so the tape remains taut but not tight. This avoids skin compression that produces lower than normal scores. Take duplicate measurements at each site and average the scores.

The Body Mass IndexClinicians and researchers frequently use body mass index (BMI), derived from body

mass in relation to stature, to evaluate the “normalcy” of one's body weight. The BMI has a somewhat higher association with body fat than estimates based simply on stature and mass.

BMI = Body mass, kg / Stature, m2

The importance of this index is its curvilinear relationship to all-cause mortality ratio: As BMI becomes larger, risk increases for cardiovascular complications (including hypertension), diabetes, and renal disease (Figure 5). The disease risk levels at the bottom of the figure represent the degree of risk with each 5-unit increase in BMI. The lowest health risk category occurs for BMIs in the range 20 to 25, with the highest risk for BMIs >40. For women,


21.3 to 22.1 is the desirable BMI range; the range for men is 21.9 to 22.4. An increased incidence of high blood pressure, diabetes, and CHD when BMI exceeds 27.8 for men and 27.3 for women.

The Surgeon General defines overweight as a BMI between 25 and 30; a BMI in excess of 30 defines obesity, a value corresponding to a moderate category of health risk. For the first time in the Unites States, overweight people (BMI over 25) outnumber people of desirable weight; shockingly, 59% percent of American men and 49% of women have BMIs that exceed 24!

The prevalence of overweight status in the United States using the BMI index is 34 million adults (15.4 million males, 18.6 million females), representing about 26% of the adult population. When analyzing the data in Figure 6 by ethnicity and sex, significantly more black, Mexican, Cuban, and Puerto Rican males and females classify as overweight compared with white males and females. Thirty-one percent of Mexican males displayed the most overweight based on BMI (31.2%), while BMI targeted 45.1% of black females as overweight.

Determine Your Body Mass Index from the following table; use weight in pounds and height in feet and inches.

Weight 100

lbs

105

lbs

110

lbs

115

lbs

120

lbs

125

lbs

130

lbs

135

lbs

140

lbs

145

lbs

150

lbs

155

lbs

160

lbs

165

lbs

170

lbs

175

lbs

180

lbs

185

lbs

190

lbs

195

lbs

200

lbs

205

lbsHeight

5'0" 20 21 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 405'1" 19 20 21 22 23 24 25 26 26 27 28 29 30 31 32 33 34 35 36 37 38 395'2" 18 19 20 21 22 23 24 25 26 27 27 28 29 30 31 32 33 34 35 36 37 375'3" 18 19 19 20 21 22 23 24 25 26 27 27 28 29 30 31 32 33 34 35 35 365'4" 17 18 19 20 21 21 22 23 24 25 26 27 27 28 29 30 31 32 33 33 34 355'5" 17 17 18 19 20 21 22 22 23 24 25 26 27 27 28 29 30 31 32 32 33 345'6" 16 17 18 19 19 20 21 22 23 23 24 25 26 27 27 28 29 30 31 31 32 335'7" 16 16 17 18 19 20 20 21 22 23 23 24 25 26 27 27 28 29 30 31 31 325'8" 15 16 17 17 18 19 20 21 21 22 23 24 24 25 26 27 27 28 29 30 30 315'9" 15 16 16 17 18 18 19 20 21 21 22 23 24 24 25 26 27 27 28 29 30 305'10" 14 15 16 17 17 18 19 19 20 21 22 22 23 24 24 25 26 27 27 28 29 295'11" 14 15 15 16 17 17 18 19 20 20 21 22 22 23 24 24 25 26 26 27 28 296'0" 14 14 15 16 16 17 18 18 19 20 20 21 22 22 23 24 24 25 26 26 27 286'1" 13 14 15 15 16 16 17 18 18 19 20 20 21 22 22 23 24 24 25 26 26 276'2" 13 13 14 15 15 16 17 17 18 19 19 20 21 21 22 22 23 24 24 25 26 266'3" 12 13 14 14 15 16 16 17 17 18 19 19 20 21 21 22 22 23 24 24 25 266'4" 12 12 13 14 15 15 16 16 17 18 18 19 19 20 21 21 22 23 23 24 24 25

In June 1998, the National Institutes of Health released the first Guidelines for identifying, evaluating, and treating obesity based on BMI values. The new classifications (2000) based on BMI are as follows:

Classification BMI Score


Underweight <18.5Normal 18.5-24.9Overweight 25.0-29.9Obesity Class I 30.0-34.9Obesity Class II 35.0-39.9Extreme Obesity

>40

The above guidelines have fueled controversy because previous guidelines established overweight at a BMI of 27 (not 25). The lowering of the demarcation value propels an additional 30 million Americans into the overweight category. This now means that 555 of the U.S. population qualify as overweight.

The following table uses the BMI to predict disease risk. A high BMI links to increased risk of death from all causes, hypertension, cardiovascular disease, dyslipidemia, diabetes, sleep apnea, osteoarthritis, and female infertility.

Competitive athletes and body builders with a high BMI due to increased muscle mass, and pregnant or lactating women, should not use BMI to infer overweightness or relative disease risk. Also, the BMI does not apply to growing children or frail and sedentary elderly adults.

BMI and Health RiskBMI Score Health Risk

>25 Minimal25 - 27 Low27 - 30 Moderate

30 - <35 High35 - <40 Very High

>40 Extremely High

Limitations of BMI for AthletesAs with height-weight tables, the BMI fails to consider the body's proportional composition.

Specifically, factors other than excess body fat (bone and muscle mass, and even the increased quantity of plasma volume induced by exercise training) affect the BMI equation. A high BMI could lead to an incorrect interpretation of overfatness in lean individuals, when in fact genetic makeup or exercise training caused the high BMI.

The possibility of misclassifying someone as overweight using BMI standards applies particularly to large-size, field-event athletes, bodybuilders, weightlifters, upper-weight class wrestlers, and professional football players. In contrast to professional football players, the average player in the NBA has a BMI of only 24.5. This relatively low BMI places them in the very-low-risk category and keeps them out of the overweight category, although they would be classified overweight by the height-weight standards.

Bioelectrical Impedance Analysis (BIA)A small, alternating current flowing between two electrodes passes more rapidly through

hydrated fat-free body tissues and extracellular water compared with fat or bone tissue due to the greater electrolyte content (lower electrical resistance) of the fat-free component. Consequently, impedance to electric current flow relates to the quantity of total body water, which in turn relates to fat-free body mass, body density, and percent body fat.

Figure 6. Dual-energy X-ray absorptiometry. Anorexic female (two left images) and a typical female (two right images) whose body fat averages 25%. The anorexic weighed 44.4 kg (97.9 lb) with a percentage body fat of 7.5%.


Using this technique, person lies on a flat, nonconducting surface. Source electrodes attach on the dorsal surfaces of the foot and wrist, and Sink electrodes attach between the radius and ulna and at the ankle.

A painless, localized electrical current is introduced, and the impedance (resistance) to current flow between the source and detector electrodes is determined. Conversion of the impedance value to body density (adding body mass and stature, sex, age, and sometimes race, level of fatness, and several girths to the equation - computes percent body fat.

Dual-Energy X-Ray Absorptiometry

Dual-energy x-ray absorptiometry (DXA), a high-technology procedure routinely used to assess bone mineral density permits quantification of fat and muscle around bony areas of the body, including regions without bone present. DXA has become an accepted clinical tool for assessing spinal osteoporosis and related bone disorders. DXA does not require assumptions about the biological constancy of the fat and fat-free components inherent when using hydrostatic weighing.

With DXA, two distinct x-ray energies (short exposure with low-radiation dosage) penetrate into bone and soft tissue areas to a depth of about 30 cm. Specialized computer software reconstructs an image of the underlying tissues. The computer-generated report quantifies bone mineral content, total fat mass, and fat-free body mass. Selected body regions can also be pinpointed for more in-depth analysis (Figure 6.)

Average Values for Body CompositionTable 1 lists average values for percent body fat in men and women throughout the United

States. Values representing ±1 standard deviation provide some indication of the variation or spread from the average; the column headed “68% Variation Limits” indicates the range for percent body fat that includes one standard deviation, or about 68 of every 100 persons measured. For example, the average percent fat of 15.0% for young men from the New York sample includes the 68% variation limits from 8.9 to 21.1% body fat. Thus, for 68 of every 100 young men measured, percent fat ranges between 8.9 and 21.1%. Of the remaining 32 young men, 16 would possess more than 21.1% body fat, while the 16 other men would have a body fat percentage less than 8.9. In general, percent body fat for young adult men averages between 12 and 15%, whereas the average fat value for women falls between 25 and 28%.

Table 1. Average percent body fat for younger and older women and men. Taken from the literature.

Group Age Range

Heightcm

Weightkg

%Fat 68%Variation Limits

Younger WomenNorth Carolina,

1962New York, 1962

17-2516-3019-23

165.0167.5165.9

55.559.058.4

22.928.721.9

17.5-28.524.6-32.917.0-26.9


California, 1968California, 1970Air Force, 1972New York, 1973North Carolina,

1975Army recruits,

1986Massachusetts,

1994Average

17-2917-2217-2617-2517-2517-3017.1-26.3

164.9164.1160.4166.1162.0165.3164.6

58.655.859.057.558.657.757.8

25.528.726.224.628.421.825.4

21.0-30.122.3-35.323.4-33.322.2-31.123.9-32.916.7-27.8

Older WomenMinnesota, 1953

New York, 1963

North Carolina, 1975

Massachusetts, 1993

Average

31-4543-6830-4040-5033-5031-5034.7-50.5

163.3160.0164.9163.1162.9165.2163.3

60.760.959.656.458.058.963.9

28.934.228.634.429.725.230.2

25.1-32.828.0-40.522.1-35.329.5-39.523.1-36.519.2-31.2

Younger MenMinnesota, 1951Colorado, 1956Indiana, 1966California, 1968New York, 1973Texas, 1977Army recruits,

1986Massachusetts,

1994Average

17-2617-2518-2316-3117-2618-2417-2517-3017.1-26.3

177.8172.4180.1175.7176.4179.9174.7178.2176.9

68.168.375.574.171.474.670.576.372.5

11.813.512.615.215.013.415.612.913.8

5.9-11.88.3-18.88.7-16.56.3-24.28.9-21.17.4-19.4

10.0-21.27.8-18.9

Older MenIndiana, 1996

North Carolina, 1976

Texas, 1977Massachusetts,

1993Average

24-3840-4827-5027-5931-50

29.8-49

179.0177.0

180.0177.1178.3

76.680.5

85.377.580.0

17.822.323.727.119.922.2

11.3-24.316.3-28.317.9-30.123.7-30.513.2-26.5


Determining Goal Body MassExcess body fat detracts from good health, physical fitness, and athletic performance.

However, no one really knows the optimum body fat or body mass for a particular individual. Inherited genetic factors greatly influence body fat distribution, and certainly impact long-term programming of body size. Average values for percent body fat for young adults approximate 15% for men and 25% for women. Women and men who exercise regularly or train for athletic competition have lower percent body fat. In contact sports and activities requiring muscular power, successful performance usually requires a large body mass with average to low body fat. In contrast, weight-bearing endurance activities require a lighter body mass and minimal level of body fat. Proper assessment of body composition, not body weight, should determine an athlete's ideal body mass. Goal body mass should coincide with optimizing sport-specific measures of physiologic functional capacity and exercise performance. A “goal” body mass target that uses a desired (and prudent) percentage of body fat can be computed as follows:

Goal body mass = Fat-free body mass / (1.00 – % fat desired)Suppose a 120-kg (265-lb) shot-put athlete, currently with 24% body fat, wishes to know

how much fat weight to lose to attain a body fat composition of 15%. The following computations provide this information:

Fat mass = body mass, kg x decimal %body fatFat mass = 120 kg x 0.24Fat mass = 28.8 kgFat-free body mass = body mass, kg – fat mass, kgFat-free body mass = 120 kg – 28.8 kgFat-free body mass = 91.2 kg

Goal body mass = Fat-free body mass, kg / 1.00 – decimal %body fatGoal body mass = 91.2 kg / (1.00 – 0.15)Goal body mass = 91.2 kg / 0.85Goal body mass = 107.3 kg (236.6 lb.)

Desirable fat loss = Present body mass, kg – Goal body mass, kgDesirable fat loss = 120 kg –107.3 kgDesirable fat loss = 12.7 kg (28.0 lb.)

If this athlete lost 12.7 kg of body fat, his new body mass of 91.2 kg would have a fat content equal to 15% of body mass. These calculations assume no change in fat-free body mass during weight loss. Moderate caloric restriction plus increased daily energy expenditure induces loss of body fat (and conservation of lean tissue.)

Obesity

Obesity: A Long-Term ProcessObesity frequently begins in childhood. For these children, the chances of becoming obese

adults increase three-fold compared with children of normal body mass. Simply stated, a child generally does not “grow out of” obesity. “Tracking” body weight through generations indicates that obese parents likely give birth to overweight children, who grows into an obese adults whose offspring’s often become obese.

Excessive fatness also develops slowly through adulthood, with ages 25 to 44 the years of greatest fat accretion. In one longitudinal study, fat content of 27 adult men increased an average of 6.5 kg over a 12-year period from age 32 to 44 years. Women gain the most weight; about 14% gained 13.6 kg (30 lb) between ages 25 and 34. The typical American man


(beginning at age 30) and woman (beginning at age 27) gains between 0.2 to 0.8 kg (0.5 - 1.75 lb) of body weight each year until age 60, despite a progressive decrease in food intake! Whether “creeping obesity” during adulthood reflects a normal biologic pattern remains unknown.

Not Necessarily OvereatingIf obesity existed as a singular disorder, with gluttony and overindulgence as causative

factors, decreasing food intake would surely be the most effective way to permanently reduce weight. Obviously, other influences, such as genetic, environmental, social, and perhaps racial are involved. Specific factors that predispose a person to excessive weight gain include eating patterns, eating environment, food packaging, body image, biochemical differences related to resting metabolic rate, basal body temperature, variations in dietary-induced thermogenesis, amount of spontaneous activity or “fidgeting,” quantity and sensitivity to satiety hormones, levels of cellular adenosine triphosphatase, lipoprotein lipase, and other enzymes, presence of metabolically active brown adipose tissue, and daily physical activity.

Regardless of the specific causes of obesity and their interactions, the treatment procedures devised so far - diets, surgery, drugs, psychological methods, and exercise, either alone or in combination - have not been particularly successful on a long-term basis. Nonetheless, optimism exists that researchers will someday devise an effective way to prevent and treat this national health affliction.

Genetics Play a RoleWhile genetic makeup does not necessarily cause obesity, it does lower the threshold for its

development; it contributes significantly to differences in weight gain for individuals fed identical daily caloric excess. Figure 7 presents data from a large number of individuals representing nine different types of relations. Genetic factors determine about 25% of the variation among people in percent body fat and total fat mass, while the larger percentage of variation relates to a transmissible (cultural) effect. In an obesity-producing environment (sedentary and stressful, with easy access to food), the genetically susceptible individual gains weight, possibly lots of it. Athletes with a genetic propensity for obesity fight a constant battle to achieve and maintain an optimal body mass and composition for competitive performance.

Figure 7. Total transmissible variance for body fat.

Figure 8. Genetic model for obesity. A malfunction of the satiety gene affects production of the satiety hormone leptin. Underproduction of leptin disrupts proper function of the hypothalamus (step#3), the center responsible for regulating the body’s fat level.


A Mutant Gene?Research with a strain of mice that enlarge to five times normal size provides evidence to

support the important genetic contribution to body weight and body fat deposition. The mutation of a gene, called obese or simply ob, probably disrupts hormonal signals that

regulate the animal’s appetite, metabolism, and fat storage, causing energy balance to tip towards fat accumulation.

Figure 8 proposes that the ob gene, normally activated in adipose tissue, produces leptin, a body fat-signaling satiety hormone that influences the appetite control center in the hypothalamus. Normally, leptin’s action blunts the urge to eat when caloric intake provides sufficient energy to maintain ideal fat stores. In this way, body fat level and the brain become intimately “connected” through a physiological pathway that regulates caloric intake. A defective gene causes inadequate leptin production. As a result, the brain receives an improper assessment of the body’s adipose status, and the urge to eat outstrips the energy need to maintain a desirable body fat level. This biological control mechanism fits nicely with the setpoint theory to explain excessive body fat accumulation. This also clarifies why obese individuals find it extremely difficult to sustain significant losses in body fat.

Physical Activity: An Important Component

Older men and women who maintain physically active lifestyles blunt the “normal” tendency to gain fat during adulthood. For young and middle-aged men who exercised regularly, time spent in physical activity related inversely to body fat level - the more exercise the less body fat. Surprisingly, no relationship emerged between body fat and caloric intake. This suggests that less demanding training, not greater food intake, produced the greater body fat levels among the active middle-aged men compared to younger, more active counterparts.


Health Risks Of ObesityConsiderable research links obesity to diverse health risks in children, adolescents, and

adults. Clear associations exist between obesity and hypertension, diabetes, and various lipid abnormalities (dyslipidemia), in addition to increased risk of cerebral and vascular diseases, alterations in free fatty acid metabolism, and atherosclerosis. However, health risks do not confront every obese person, suggesting that obesity represents a nonuniform, heterogeneous condition. Indeed, evidence accumulated over the last 15 years confirms the heterogeneous nature of obesity, not only its cause (s) but also its complications. Nevertheless, obesity should be viewed as a chronic medical condition because multiple biologic hazards of premature illness and death exist at surprisingly low levels of excess body fat. Some researchers believe that even modest obesity powerfully predicts heart disease risk, equal to cigarette smoking, elevated blood lipids, physical inactivity, and hypertension. Staggering economic expenses arise from obesity-related medical complications; by the year 2000, 12% of the cost of illness in the US will relate directly or indirectly to excessive body fatness.

How Fat Is Too Fat?Three criteria can evaluate a person’s level of body fatness:

1. Percent body fat2. Fat patterning3. Fat cell size and number

Percent BodyThe demarcation between normal body fat levels and obesity often becomes arbitrary. The

“normal range” of body fat in adult men and women has been identified as at least plus or minus one unit of variation (standard deviation) from the average population value. That variation unit equals –5% body fat for men and women between the ages 17 and 50 years. Within this statistical boundary, overfatness corresponds to any percent body fat value above the average value for age and sex, plus 5 percentage points. For young men, whose fat mass averages 15% of total body mass, the borderline for obesity equals 20% body fat. For older men, average percent fat equals about 25%. Consequently, a body fat content in excess of 30% represents overfatness for this group. For young women, obesity corresponds to a body fat content above 30%, while for older women borderline obesity begins at 37% body fat.

A problem with these age-specific demarcations for obesity lies in the assumption that men and women “normally” become fatter with aging. However, this does not necessarily occur for physically active older men and women. If lifestyle actually accounts for the greatest portion of body fat increase during adulthood, then the criterion for overfatness could justifiably represent the standard for younger men and women: above 20% for men and above 30% for women.


THE RISKS OF BEING YOUNG AND FATChildhood obesity represents a more significant adult health risk than obesity developed in adulthood. A 55-year follow-up indicates that individuals who became overweight in childhood or adolescence had significantly greater risk of a broad range of adverse health effects compared to normal-weight counterparts. Surprisingly, with the exception of diabetes, these effects were independent of the children’s eventual weight as an adult.

Figure 9. Male and female fat patterning including the waist-to-hip girth ratio threshold for significant health risk.


Gradations of obesity progress from the upper limit of normal (20% for men and 30% for women) to as high as 50 to 70% of body mass. Common terms for gradations in obesity include pleasantly plump for those just above the cut-off, to moderately obese, excessively obese, massively obese, and morbidly obese. The last category includes people who weigh in the range of 170 to 275 kg (385 to 600 lb) and whose fat content exceeds 55%. In such cases, body fat can exceed fat-free body mass, and obesity becomes life threatening.

Fat PatterningFat cells (adipocytes) display remarkable diversity depending on their anatomic location.

Some cells efficiently “capture” excess nutrient calories from the bloodstream and synthesize them into triglycerides for storage, while other adipocytes not only accumulate triglycerides but readily release this form of stored energy for use by other tissues. This explains why

certain fat deposits exhibit resistance to reduction and others expand and contract readily in response to the body’s energy balance. Research now indicates that the patterning of adipose tissue distribution, independent of total body fat and body weight, alters the health risk from obesity.

Studies using MRI and CT-scanning to precisely discriminate subcutaneous from visceral (intra-abdominal) adipose tissue (V-AT) show that V-AT accumulation in excess of 130 cm2 relates to an altered metabolic profile that includes:

Hyperinsulinemia Insulin resistance and glucose

intolerance Hypertriglyceridemia Reduced high-density lipoprotein

(HDL) cholesterol concentrations Increased apolipoprotein B, the

regulatory protein constituent of the harmful LDL cholesterol

Excessive insulin production and depressed insulin sensitivity that characterizes V-AT obesity not only increases risk for noninsulin dependent diabetes mellitus, but also risk for ischemic heart disease. Thus, visceral obesity represents an additional component of the insulin-resistant, dyslipidemic syndrome, which represents the most prevalent cause of coronary artery disease in industrialized countries.


STANDARDS FOR OVERFATNESSMen - above 20% body fat

Women - above 30% body fat


The notion that body fat distribution represents an important component in the clinical assessment of obese patients first emerged in 1947, and has been confirmed in subsequent epidemiological studies. A preferential abdominal fat accumulation, first described as android obesity (male-pattern or central obesity), exists largely among overweight patients with hypertension, type 2 diabetes, and coronary heart disease. This contrasts to the lower health risks of gynoid obesity (female-pattern or peripheral obesity), where the majority of excess fat deposits in the body’s gluteal and femoral regions. Figure 9 shows examples of the apple (android) and pear (gynoid) body shape types.

The waist-to-hip girth ratio (WHR) (Figure 9) often represents the initial clinical assessment of V-AT. Ratios exceeding 0.80 for women and 0.95 for men indicate excessive visceral fat accumulation, which predicts increased risk of death from coronary artery disease and other illnesses. An elevated waist-to-hip girth ratio predicts health risk with greater accuracy than the popular measurement of body mass index (BMI).



1. Archimedes’ principle

2. Body mass index

3. Body volume

4. Density

5. Desirable body mass

6. Essential fat

7. Fat mass

8. Skinfold

9. Fat-free body mass

10. Hydrostatic weighing

11. Lean body mass

12. Minimal weight


13. Overweight

14. Reference man

15. Reference woman

16. Sex-specific fat

17. Specific gravity

18. Storage fat

19. Underweight

20. Android obesity

21. Gynoid obesity

22. Obesity

STUDY QUESTIONS

Gross Composition of the Human BodyList three major structural components of the human body and their percentage as represented by the reference man and woman. (Hint: Refer to Figure 18.1 in your textbook.)

Structural Component Reference Man Reference Woman1.


2.

3.

Reference Man and Reference WomanCompare body mass, stature, total fat, and storage and essential fat for the reference man and women.

Reference Man Reference Women

Stature, cm

Body mass, kg

Total fat, kg

Total fat, %

Storage fat, kg

Storage fat, %

Essential fat, kg

Essential fat, %

Essential and Storage FatEssential FatGive the function and location of essential fat and sex-specific essential fat in humans.

Function Location

Essential fat

Sex-specific fat

Storage FatGive the function and location of storage fat in humans.

Function

Location


Fat-Free Body Mass and Lean Body MassWhat is the suggested “healthy” lower level of percent body fat in males?

Minimal Body MassWhat is the suggested “healthy” lower level of percent body fat in females?

Underweight and ThinWhat precisely is meant by the terms “underweight" and "thin?”

Underweight

Thin

Leanness, Exercise, and Menstrual IrregularityDescribe the lower limit of body fat believed required for maintaining normal menstrual function?

Leanness Not the Only FactorList four factors associated with menstrual dysfunction.

1. 2.

3. 4.

Methods to Assess Body Size and CompositionList two general procedures to evaluate body composition.

1.

2.

Direct AssessmentDescribe a major limitation of the direct method of body composition assessment in humans.


Indirect AssessmentList three indirect procedures commonly used to assess body composition.

1. 3.

2.

Hydrostatic Weighing (Archimedes’ Principle)State Archimedes principle of water displacement.

Determining Body DensityComplete the formula: Specific gravity = ______________÷______________.

Calculate the approximate body volume of a person weighing 50 kg and 2 kg when submerged underwater.

Computing Percent Body Fat and Mass of Fat and Fat-Free TissueCompute the percent body fat of a person whose body density equals 1.0742 g/cc.

Give the equation and compute the fat mass for a person weighing 63.4 kg with body fat of 10.8%.

Equation

Fat mass

Body Volume MeasurementWrite the equation to compute body volume by hydrostatic weighing.

Body Volume Measurement By Air DisplacementExplain the principle underlying the use of the BOD POD for body volume determinations.

Skinfold MeasurementsThe close relationship between these three variables provides the rationale for using skinfold measurements to predict body composition.


1. 3.

2.

Girth MeasurementsList two advantages of girth measurements over skinfolds to assess body fat.

1.

2.

The Body Mass IndexWrite the formula to compute body mass index.

Limitations of BMI For AthletesGive one limitation of the BMI and its importance to athletes?

Limitation

Importance to athletes

Average Values for Body CompositionGive the average percent body fat for college age males and females.

Males Females

Determining Goal Body MassWrite the equation to compute desirable body mass.

A 20-year old man weighs 89 kg with 22% body fat. If this man reduces body fat to a desired 12% level, determine (a) his new body mass, and (b) total fat mass lost? Assume all weight loss represents fat.

New body mass

Total fat loss

ObesityObesity: A Long-Term Process


Discuss the trend for weight gain in adult men and women as they age.

Not Necessarily OvereatingList three factors that predispose a person to excessive weight gain.

1. 3.

2.

Genetics Play a RoleHow much of the variation in weight gain among individuals can be accounted for by genetic factors?

A Mutant Gene?Describe the role of the mutant “obese” gene in the obesity development.

Physical Activity: An Important ComponentDiscuss how increases in body fat with age relate to physical inactivity than age itself.

Health Risks of ObesityDoes excess body weight or excess body fat relate more strongly to heart disease risk?

How Fat is Too Fat?List three criteria for evaluating a person’s level of body fatness.

1. 3.

2.

Percent BodyWhat percent body fat level indicates borderline obesity in adult men and women?

Men


Women

Fat PatterningList the 2 types of fat patterning

1.

2.


PRACTICE QUIZ1. Essential body fat:

a. same for males and femalesb. women have morec. men have mored. non-existente. none of the above

2. FFM:a. fat free massb. fat massc. body mass minus lean body massd. same for males and femalese. none of the above

3. Minimal body mass:a. same for males and femalesb. women’s lowerc. men’ lowerd. body mass minus fat free masse. none of the above

4. Archimedes’ principle:a. evaluates specific gravityb. evaluates body fatc. predicts optimal body weightd. does not apply to humanse. none of the above

5. Body density:a. weight divided by FFMb. weight divided by fatc. weight divided by volumed. volume divided by weighte. none of the above

6. BMI:a. mass ÷ stature squaredb. mass ÷ volumec. same as body surface aread. determines amount of body fate. none of he above

7. True: False. Goal body mass = FFM ÷ FM:a. Trueb. False

8. Leptin:a. satiety hormoneb. enzyme responsible for fat

hypercellularityc. found in muscle cellsd. only found in individuals with

high BMI’se. none of the above

9. True or False: FFM = Body mass – fat massa. Trueb. False

10. Dyslipidema:a. found in leptin cellsb. enzyme found in the obesec. lean individuals don’t produce

this type of fatd. lipid abnormalitiese. none of the above

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