Nieman DC. Exercise Testing and Prescription: A Health ...
Chapter 5 Body Composition
Rationale for measuring body composition <ul><li>To assess the decrease in body fat weight that occurs in response to a weight management program. </li></ul><ul><li>To help athletes determine the best body composition for performance. </li></ul><ul><li>To monitor fat and fat-free weight in patients with disease . </li></ul><ul><li>To track long-term changes that occur in body fat and fat-free mass with aging. </li></ul>
Body Composition = ratio of fat to fat-free mass (see definitions, Table 5.1). Figure 5.1a compares 2- and 4-compartment models. Figure 5.1b shows reference proportions for 4-compartment model.
The Brozek (4.57/body density – 4.142) and Siri (4.95/body density – 4.50) equations estimate percent body fat from body density. Fat free mass varies among different groups, and Table 5.2 summarizes recommended equations. Weight measurement alone cannot accurately determine body fat status (see Figure 5.2). People vary widely in somatype (or body build) (see Figure 5.3). The 1983 Metropolitan Height-Weight Table, and other weight tables, have multiple deficiencies (see Tables 5.3,5.5) and is no longer recommended.
Measuring Weight and Height (see growth charts, Figures 5.5 to 5.9). <ul><li>Body weight should be measured on a physician’s balance-beam scale with minimal clothing and no shoes. </li></ul><ul><li>Height should be measured with a stadiometer: </li></ul><ul><ul><li>No shoes, heels together, back straight, heels, buttocks, shoulders, and head touching the wall, standing as tall as possible, and looking straight ahead. </li></ul></ul><ul><ul><li>Have individual inhale deeply and hold breath. </li></ul></ul>
Body mass index (BMI) is a commonly used estimate of obesity (especially in population studies and surveys). The Quetelet Index is the most popular BMI estimate: kg/m 2 (also see Table 5.8 and Figure 5.11 for non-math methods of estimating BMI) . Table 5.7 shows the relationship between BMI and percent body fat (r=0.70, SEE 5% body fat). See Fig. 5.12 for population trends in BMI.
Table 5.9 summarizes the 1998 NHLBI Obesity Education Initiative guidelines for classifying BMI, with disease risk estimated when also related to waist circumference. (Also see CDC growth charts that classify BMI for boys and girls, aged 2-20 years, in Figures 5.13 and 5.14). Also see Box 5.1 for USDA system of classifying BMI.
The most widely used body composition estimate is the skinfold measurement technique. When performed correctly, skinfold measures provide an fairly good estimate of percent body fat (r ≥ 0.80 with underwater weighing). The goal is to measure a double fold of skin and subcutaneous tissue (with sides of skinfold approximately parallel) (Fig. 5.15). The thicker the fat layer, the wider the fold (Fig. 5.16).
Basic Rules for Taking Skinfolds <ul><li>Take skinfold measurements on the right side of the body (most skinfold equations were developed from measurements on the right side). </li></ul><ul><li>Do not take measurements when the subject's skin is moist (ensure that the skin is dry, and has no lotion). Also do not take measurements immediately after exercise or when the person being measured is overheated because the shift of body fluid to the skin will inflate normal skinfold size. </li></ul><ul><li>To reduce error during the learning phase, skinfold sites should be precisely determined, marked, and verified by a trained instructor. The largest source of error in skinfold testing is inaccurate site selection. </li></ul>
Skinfold Rules (continued) <ul><li>Firmly grasp the skinfold with the thumb and index finger of the left hand, and pull away. </li></ul><ul><li>Hold the caliper in the right hand, perpendicular to the skinfold and with the skinfold dial facing up and easily readable. Place the caliper heads ¼-½ inch away from the fingers holding the skinfold. Try to visualize where a true double-fold of skin thickness is, and place the caliper heads there. </li></ul><ul><li>Read the caliper dial to the nearest 1 millimeter within 4 seconds. During the measurement, ensure that the left thumb and forefinger maintains the shape of the skinfold. </li></ul><ul><li>Take a minimum of 2 measurements at each site (at least 15 seconds apart). If the 2 values are within 10% of each other, take the average. </li></ul>
Thigh Skinfold (see Figures 5.20 and 5.21) Vertical fold on anterior thigh, midway between inguinal crease and proximal border of patella.
Suprailiac Skinfold (Figs. 5.23 and 5.24) 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).
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).
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.
Figure 5.28 Average triceps skinfold of American males and females (mean is middle dark bar, with 15 th and 85 th percentiles)
Abdomen Skinfold Site (Fig. 5.19) Horizontal 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.
Subscapular Skinfold (Fig. 5.26) Diagonal fold just below the inferior angle of scapula.
Midaxillary Skinfold (Fig. 5.25) Horizontal fold taken on midaxillary line at level of xiphisternal junction. In the Jackson-Pollock procedure, a vertical fold is used at this site.
Medial Calf (Fig. 5.27) A vertical skinfold on the inside of the calf at the level of maximum circumference.
Figure 5.29 Body fat standards for children/youth ages 6-17 years using the triceps and subscapular skinfolds (sum). Figure 5.30 Body fat standards for children/youth ages 6-17 years using the triceps and medical calf skinfolds (sum). Table 5.10 Jackson and Pollock generalized body composition equations. Use Table 5.2 for age- and sex-specific equations to convert body density to percent body fat. Figure 5.31 Nomogram for estimating percent body fat from sum of three skinfolds.
Table 5.12 Body Fat Ranges for Ages 18 and Older ≥ 32% ≥ 25% Unhealthy range (too high) 24-31% 16-24% Acceptable range (higher end) 9-23% 6-15% Acceptable range (lower end) ≤ 8% ≤ 5% Unhealthy range (too low) Female Male Classification
<ul><ul><ul><li>Table 5.12 Average Body Fat Ranges for Elite Athletes </li></ul></ul></ul><ul><ul><ul><li>Males Females </li></ul></ul></ul><ul><li>Endurance Athletes 4-15% 12-26% </li></ul><ul><li>Athletes in Sports that </li></ul><ul><li>Emphasize Leanness 4-10% 10-19% </li></ul><ul><li>Team/Dual Sport Athletes 7-21% 18-27% </li></ul><ul><li>Power Athletes 5-20% 17-30% </li></ul>
BIA: See Table 5.14. Leg-to-Leg BIA (Fig. 5.38)
Figure 5.40 The ratio of waist-to-hip circumference (WHR) has been used to determine android vs. gynoid type of obesity. The waist circumference is the smallest circumference below the rib cage and above the umbilicus. The hip circumference is the largest circumference of the buttocks-hip area. The waist circumference alone is more commonly used than the WHR.