Body Composition

Body Composition To determine recommended body weight, we need to assess body composition Fat mass or percent body fat Non-fat component or lean body mass Percent body fat (fat mass) Proportional amount of fat in the body based on the person’s total weight Includes both essential fat and storage fat Lean body mass: body weight without body fat

Body Composition Recommended body weight (healthy weight) Body weight at which there seems to be no harm to human health Body composition Fat and non-fat components of the body Used to assess recommended body weight

Essential and Storage Fat Essential fat is needed for normal physiological functions 3% of total weight in men; 12% in women Storage fat is fat stored in adipose tissue Insulator to retain body heat Energy substrate for metabolism Padding against physical trauma

Typical Body Composition Figure 4.1. Typical body composition of an adult man and woman.

Techniques to Assess Body Composition Dual energy x-ray absorptiometry (DXA) Method to assess body composition that uses very low-dose beams of x-ray energy to measure total body fat mass, fat distribution pattern, and bone density SEE ± 1.8% Due to costs, DXA is not readily available to most fitness participants

Techniques to Assess Body Composition (cont’d.) Hydrostatic weighing Underwater technique to assess body composition; considered the most accurate of the body composition assessment techniques. “Regular” weight vs. underwater weight (fat buoyancy) SEE ± 2.5% Some people are aquaphobic

Techniques to Assess Body Composition (cont’d.) Air displacement Technique to assess body composition by calculating the body volume from the air replaced by an individual sitting inside a small chamber (Bod Pod) SEE ± 2.2% Percent body fat is about 5% higher than hydrostatic weighing

Techniques to Assess Body Composition (cont’d.) Skinfold thickness Technique to assess body composition by measuring a double thickness of skin at specific body sites Based on the principle that fat under the skin (subcutaneous fat) is proportional to total body fat SEE ± 3.5 percent

Calipers Used to Assess Skinfold Thickness Various types of calipers used to assess skinfold thickness

Procedure for Skinfold Measurements Figure 4.2. Procedure and anatomical landmarks for skinfold measurements.

Techniques to Assess Body Composition Girth measurements Assesses body composition by measuring circumferences at specific body sites Women: upper arm, hip, and wrist Men: waist and wrist Requires little equipment SEE ± 4%

Girth Measurements Figure 4.3. Procedure for body fat assessment according to girth measurements.

Techniques to Assess Body Composition (cont’d.) Bioelectrical impedance Assesses body composition by running a weak electrical current through the body Fat tissue is a less efficient conductor of electrical current than lean tissue Simple to administer Accuracy is questionable Measurements may be off by as much as 10%

Techniques to Assess Body Composition (cont’d.) Body mass index (BMI) Technique to determine thinness and excessive fatness that incorporates height and weight to estimate critical fat values at which the risk for disease increases BMI = [Body weight in pounds x 705 ÷ (height in inches)2]

Mortality Risk versus BMI Figure 4.4. Mortality risk versus body mass index (BMI).

Disease Risk and BMI Table 4.7. Disease Risk According to Body Mass Index (BMI)

Techniques to Assess Body Composition Location of fat is a better predictor of increased risk for disease than total body fat: Android obesity (“apple” shape) is fat stored in the trunk or abdominal area Gynoid obesity (“pear” shape) is fat stored around the hips and thighs Waist-to-Height Ratio (WtHR): keep your waist circumference (WC) half of your height

Disease Risk and Waist Circumference Table 4.8. Disease Risk According to Waist Circumference (WC)

Risk Factors: VSC, SBC, and RTP Fat Figure 4.7. Visceral (VSC) fat is a greater risk factor for heart diseases, stroke, hypertension diabetes, and cancer than subcutaneous (SBC) or retroperitoneal (RTP) fats.

Body Weight and Aging Your recommended body weight is based on your age and gender Because lean tissue decreases with age, one extra percentage point is allowed for every additional decade of life

Importance of Regular Body Composition Assessment Adults in the US tend to gain 1 to 2 pounds per year, and lose ½ pound lean tissue per year These changes can only be detected by assessing body composition periodically To make valid comparisons, use the same technique for both pre- and post-program assessments

Body Composition Changes Figure 4.9. Typical body composition changes for adults in the United States.

Assess Yourself Have you been able to maintain your body weight at a stable level during the past 12 months? Do you understand the following concepts? Body composition vs. body weight Recommended body weight Techniques for assessing body composition Effects of BMI and waist circumference on risk for disease