Understanding Body Composition and Obesity

1. chapter6 Body Composition Dixie L. Thompson

2. Important Terms Fat mass Fat-free mass Percent body fat Obesity Overweight Body fat distribution or fat patterning Android-type obesity Gynoid-type obesity

3. Obesity Is a Major Health Problem • Nearly two thirds of American adults are classified as either overweight or obese. • The following conditions are linked with obesity: • Type 2 diabetes • Coronary artery disease • Hypertension • Degenerative joint disease • Abnormal lipid profile

4. Common Techniques in Body Composition Assessment • Hydrostatic weighing • Bioelectrical impedance • Skinfold measurements • Girth measurements • Body mass index

5. Hydrostatic Weighing • Often referred to as a criterion method • 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

6. 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).

7. Formula for CalculatingHydrostatic Weight

8. Two-Compartment Density Models • 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. • Fortunately, there are two-compartment models for various populations. • Both hydrostatic weighing and air displacement plethysmography use two-compartment models.

9. 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)

10. 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. • It is critical that the person being tested is normally hydrated.

11. Skinfold Measurements • Because there is a correlation between subcutaneous fat and total body fatness, the thickness of skinfolds can be used to estimate %BF. • The accuracy is typically within 4% of hydrostatic weighing.

12. 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.

13. 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

14. 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.

15. 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

16. 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.

17. Formula for CalculatingTarget Body Weight