copyright © 2006 lippincott williams & wilkins. human energy transfer during exercise chapter 6

Copyright © 2006 Lippincott Williams & Wilkins.

Human Energy Transfer During Exercise

Human Energy Transfer During Exercise

Chapter 6Chapter 6


ObjectivesObjectives

• Identify the body’s three energy systems, and explain their relative importance to exercise intensity and duration

• Describe differences in blood lactate threshold between sedentary and trained individuals

• Outline the time course for oxygen uptake during 10 minutes of moderate exercise


Objectives (cont’d)Objectives (cont’d)

• Draw a figure showing the relationship between oxygen uptake and exercise intensity during progressively increasing increments of exercise to maximum

• Differentiate between the body’s two types of muscle fibers


Objectives (cont’d)Objectives (cont’d)

• Explain differences in the pattern of recovery oxygen uptake from moderate and exhaustive exercise, and include factors that account for EPOC from each exercise mode

• Outline optimal recovery procedures from steady-rate and non–steady-rate exercise


Energy Systems Energy Systems

• Immediate energy– ATP-PCr

• Short-term energy– Lactic acid system

• Long-term energy– Aerobic system


ATP-PCr System ATP-PCr System

• Performances of ultra-short duration (< 6 seconds) and high intensity require an immediate and rapid supply of energy– 100-m sprint– 25-m swim – Smashing a tennis ball during the serve– Thrusting a heavy weight upwards


ATP-PCr System (cont’d)ATP-PCr System (cont’d)

• High-energy phosphates — phosphagens– Stored within skeletal muscle

• Adenosine triphosphate (ATP)• Phosphocreatine (PCr)

CP + ADP C + ATP


Lactic Acid SystemLactic Acid System

• During intense exercise, intramuscular stored glycogen provides energy to phosphorylate ADP during glycogenolysis, forming lactate


Lactic Acid System (cont’d)


• Performances of short duration and high intensity that require rapid energy transfer that exceeds that supplied by phosphagens – 400-m sprint– 100-m swim – Multi-sprint sports




• The lactate threshold (LT)– The exercise intensity prior to the

abrupt increase in blood lactate– A.k.a onset of blood lactate

accumulation (OBLA)


Did You Know?Did You Know?

• World class athletes can sustain exercise intensities at 85 to 90% of their maximum capacity for aerobic metabolism before blood lactate accumulates


Lactate ShuttlingLactate Shuttling

• It has been shown that lactate produced through glycogenolysis in one cell may be shuttled to another cell to provide fuel for further oxidation

• Thus, skeletal muscle is not only a major site of lactate production but is also a primary tissue for lactate removal via oxidation


Aerobic Energy SystemAerobic Energy System

• Aerobic metabolism provides the greatest proportion of energy transfer, particularly when exercise duration extends beyond 2 to 3 minutes


Aerobic Energy System (cont’d)


• 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 at the initiation of exercise




• Maximal oxygen consumption ( )– The highest oxygen uptake achieved

despite increases in exercise intensity– Represents an individual’s capacity for

aerobically resynthesizing ATP

2maxOV


Muscle Fiber TypesMuscle Fiber Types

• Two distinct muscle fiber types exist in humans– Fast-twitch (FT) or type II muscle

fibers– Slow-twitch (ST) or type I muscle fiber


Muscle Fiber Types (cont’d)


• Type I muscle fibers are highly oxidative and are designed for prolonged endurance activities

• Type IIb muscle fibers are highly glycolytic and are designed for explosive activities




• Type IIa muscle fibers are both oxidative and glycolytic and are designed for activities that are both aerobic and anaerobic in nature


Key PointKey Point

• The body’s energy systems should be viewed along a continuum of exercise bioenergetics


Oxygen Uptake During Recovery: “Oxygen Debt”


• Oxygen consumption following exercise remains elevated for several minutes to several hours depending on the intensity and duration of exercise

• This elevation in oxygen consumption is often referred to as the “Oxygen Debt” or Excess Postexercise Oxygen Consumption (EPOC)



(cont’d)


(cont’d)• Traditional view

– Oxygen debt theory• Alactacid oxygen debt• Lactacid oxygen debt

• Modern view– EPOC theory


Optimal RecoveryOptimal Recovery

• Active aerobic exercise in recovery accelerates lactate removal

• Moderate aerobic exercise during recovery is clearly better for facilitating lactate removal compared to passive recovery

copyright © 2006 lippincott williams & wilkins. human energy transfer during exercise chapter 6

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