Dixie L. Thompson chapter 6 Body Composition

Important Terms Fat 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= 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 D b = lower body fat %.

Formula for Calculating Hydrostatic 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 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) ] x 100 Brozek Equation - % body fat = [(4.57 / Db) ] x 100

Two-Compartment Density Models NOT 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 ÷ D b – 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) 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 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 % 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 Impedance Analysis (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 Impedance Analysis (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 weight 25 to 29.9 kg · m –2 = overweight ≥30 kg · m –2 = obese

Body Mass Index (BMI) The ratio of mass to height 2 BMI = body mass (kg) / body height (m) 2 for example BMI = 80 (kg) / (m) = kg/m 2

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 Calculating Target 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).