dixie l. thompson chapter 6 body composition. important terms fat mass - mass of fat tissues in the...
TRANSCRIPT
Dixie L. Thompson
chapter
6 Body Composition
Important TermsFat mass - mass of fat tissues in the body.
Fat-free mass - a.k.a. lean body mass.
Percent body fat - % of body composed of fat.
Obesity - abnormal excess of fat tissue.
BMI > 30, Men >25%, Women >38%
Overweight - above recommended wt range.
Body fat distribution or fat patterning
Android-type obesity - Males primarily, closely linked with CHD.
Gynoid-type obesity - mainly seen in females
Essential Fat
• amount of body fat % necessary for good health.
• Allows for temperature regulation, joint cushioning, providing energy.
• 8-12% for women
• 3-5% for men
Common Techniques in Body Composition Assessment
• Skinfold measurements• Hydrostatic weighing• Bioelectrical impedance• Girth measurements• Body mass index
SKINFOLDS
• 3 SITE, 4 SITE, 7 SITE• r=0.70-0.90 with hydrostatic weighing• Rationale: The amount of
subcutaneous fat is proportional to the amount of body fat.
• 1/3 of fat is located subcutaneously• Varies due to age, gender, ethnicity -
must choose the proper Db equation.
Thigh Skinfold (see Figures 5.20 and 5.21)Vertical fold on anterior thigh, midway between
inguinal crease and proximal border of
patella.
Nieman DC. Exercise Testing and Prescription: A Health-Related Approach. 6/e. Copyright ©2007 McGraw-Hill Higher Education. All rights reserved.
Suprailiac Skinfold
Diagonal fold just above iliac crest at
the midaxillary line.
(In the Jackson-Pollock procedure, a diagonal fold is taken with the natural angle
of the iliac crest at the anterior axillary line
immediately superior to the iliac crest).
Nieman DC. Exercise Testing and Prescription: A Health-Related Approach. 6/e. Copyright ©2007 McGraw-Hill Higher Education. All rights reserved.
Nieman DC. Exercise Testing and Prescription: A Health-Related Approach. 6/e. Copyright ©2007 McGraw-Hill Higher Education. All rights reserved.
Chest Skinfold (Fig. 5.18)
Diagonal fold, between anterior axillary fold and nipple, taken one inch from anterior axillary fold.
(In the Jackson-Pollock procedure, the chest/pectoral skinfold site is one half the distance between the anterior axillary line and the
nipple for men, and one third of this distance for women).
Nieman DC. Exercise Testing and Prescription: A Health-Related Approach. 6/e. Copyright ©2007 McGraw-Hill Higher Education. All rights reserved.
Triceps Skinfold (Fig. 5.22)
Vertical fold on posterior aspect of arm, midway between lateral projection of acromion process and inferior margin
of olecranon process.
Nieman DC. Exercise Testing and Prescription: A Health-Related Approach. 6/e. Copyright ©2007 McGraw-Hill Higher Education. All rights reserved.
Abdomen Skinfold Site (Fig. 5.19)
Vertical fold, one inch to the right side of and ½ inch below the navel.
The Jackson-Pollock procedure uses a vertical fold 2 cm to the right of the umbilicus.
Skinfolds
• Accuracy is dependant on tester
• +3.5% accuracy assuming qualified tester
• Accuracy decreases with higher levels of obesity
• Somewhat up close and personal
Accuracy in Measuring Skinfolds
To make the measurements as accurate as possible,– accurately locate the skinfold site,– accurately measure the skinfold, and– choose the appropriate equation for converting
skinfold thickness into %BF.
Hydrostatic Weighing• Often referred to as a criterion method
or gold standard.
• Based on Archimedes’ principle: A person with proportionally more lean mass will weigh more underwater than a person with less lean mass (see figure 6.1)
• Used to calculate total body density
Archimedes Principle
• Bone and Muscle Tissue are denser than water, fat tissue is less dense.
• More FFM or muscle = weighing more in water = higher Db = lower body fat %.
Formula for CalculatingHydrostatic Weight
100 mL = volume of air trapped in gastrointestinal tract that cannot be measured.
Body Density (Db) = body mass (g) / body volume (mL)
Db = Wa / {[(Wa - Ww) / Dw] - (RV + 100 mL)}where; Db = body density (g/mL)
Wa = body mass out of water
Ww = body mass underwater
Dw = density of water (g/mL)
RV = residual lung volume (mL)
100 mL = volume of air trapped in gastrointestinal tract that cannot be measured.
Siri Equation - % body fat = [(4.95 / Db) - 4.50] x 100Brozek Equation - % body fat = [(4.57 / Db) - 4.142] x 100
Two-Compartment Density ModelsNOT ON TEST
• Assume that body is divided into fat mass (FM) and fat-free mass (FFM).
• Assume a constant density of fat and fat-free tissues among individuals.
• Siri (1961) gives a common model: %BF = 495 ÷ Db– 450.
• When components of the FFM differ from the assumed values, estimation of %BF is compromised. Examples: Bone density, hydration. Bone density will vary between races.
• Fortunately, there are two-compartment models for various populations.
• Both hydrostatic weighing and air displacement plethysmography use two-compartment models.
HYDROSTATIC WEIGHING• Accurate but requires costly equipment• Time consuming and very personal• Subjects must follow pre-test guidelines
completely. (no food ingestion 4 hrs prior, smoking, caffeine, exercise).
• 5-10 trials necessary - FATIGUING • light weight clothing needed, removal of air
bubbles from suit, hair, and skin while underwater. • RV can be done before, during or after.• RV errors can cause bf to be off by 3%.
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Air-displacement plethysmography (BodPod)
$37,999 , mobile, 5 minutes• Relatively new - 1989• Must wear tight fitting swimsuit and cap• Claustrophobia a concern with some• Fitness Center and Pediatric versions
Air-Displacement• Subject sits in a calibrated "pod" and air is
displaced instead of water.
• Similar results to hydrostatic weighing
• Appears to be an accurate alternative - standard error of 2.2 - 3.7% body fat.
• "Increased research and technology should yield more accurate results in the future." In other words RV is a concern.
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Bioelectrical ImpedanceAnalysis (BIA)
• Electrical current travels more easily through tissue containing water and electrolytes.
• Fat does not contain much water; therefore, electrical flow is impeded.
• Fat can be estimated by the impedance encountered when electrical currents pass through the body.
(continued)
Bioelectrical ImpedanceAnalysis (BIA) (continued)
• There are a number of commercially available BIA devices.
• Values are typically within 4% of those obtained with hydrostatic weighing.
• It is important to choose the proper equation for estimating %BF. The relationship between % BF and impedance varies among populations.
• It is critical that the person being tested is normally hydrated.
BIA Problems
• Electrolyte status may be altered due to: • alcohol consumption (48 hrs)• food consumption (4 hrs)• recent exercise (12 hrs)• diuretic therapy (Physician approved)• menstrual cycle (avoid 3 days prior through
three days following)• Oil and lotions should be removed from the
skin
Common Girth Measurements• Waist: most narrow part of the torso
between the xiphoid process and the umbilicus
• Abdomen: circumference of the torso at the level of the umbilicus
• Hips: maximal circumference of the buttocks above the gluteal fold
• Thigh: largest circumference of the right thigh below the gluteal fold
Abdominal Obesity• A waist-to-hip ratio of ≥0.95 for
men or ≥0.86 for women is considered too high according to ACSM standards.
• A waist circumference greater than 102 cm in men or 88 cm in women significantly increases the risk of obesity-related disease.
Body Mass Index (BMI)
• Criterion used to classify adequacy of weight for height
• Does not indicate level of body fatness• Weight (in kilograms) divided by
squared height (in meters)<18.5 kg · m–2 = underweight
18.5 to 24.9 kg · m–2 = normal weight25 to 29.9 kg · m–2 = overweight
≥30 kg · m–2 = obese
Body Mass Index (BMI)
The ratio of mass to height2
BMI = body mass (kg) / body height (m)2
for example
BMI = 80 (kg) / 1.72 (m) = 27.68 kg/m2
Why Use BMI?• High BMI associated with a higher
mortality rate due to CVD, Cancer, Diabetes, and other diseases.
• Easy - Private
• No Training Involved
• Better than HT/WT tables
Why Not To Use BMI• Does not reflect actual body fat content
• Does not consider muscle weight
• +5 error rate
Calculating Target Body Weight
• It is often important to help clients determine a healthy and reasonable weight.
• Calculating target body weight requires knowledge of current body weight, %BF, and desired %BF.
Formula for CalculatingTarget Body Weight
Comparison of Two Individuals With Same Total Mass But
Different LBM
Adapted from M.L. Pollock and J.H. Wilmore, 1990, Exercise in health and disease, 2nd ed. (Philadelphia: Saunders).