Chapter 4 Body Composition

1. Outline: Essential & Storage Fat Techniques to Assess Body Composition Determining Recommended Body Weight Importance of Regular Body Composition Assessment Chapter 4Body Composition

2. Key Terms • Body composition: The fat and nonfat components of the human body; important in assessing recommended body weight • Percent body fat: Proportional amount of fat in the body based on the person’s total weight; includes both essential and storage fat • Lean body mass: Body weight without body fat • Recommended body weight: Body weight at which there seems to be no harm to human health (healthy weight)

3. Key Terms • Overweight: An excess amount of weight against a given standard such as height or recommended percent body fat • Obesity: An excessive accumulation of body fat usually at least 30% above recommended body weight

4. Height/Weight Tables An individual might appear to be overweight according to height/weight tables but not have too much body fat Examples are football players, body builders, other athletes with large muscles Some people may look skinny or underweight when they actually are overweight because of their high body fat Physical inactivity and a constant negative caloric balance both cause a loss in lean body mass

5. Essential and Storage Fat Total fat in the human body can be classified into two types Essential fat: Minimal amount of body fat needed for normal physiological functions; constitutes about 3% of total weight in men and 12% in women Storage fat: Body fat in excess of essential fat; stored in adipose tissue

6. Typical body composition of an adult man & woman • Essential fat constitutes about 3% of the total weight in men and 12% in women

7. Body Composition Storage fat serves 3 basic functions: As an insulator to retain body heat As an energy substrate for metabolism As padding against physical trauma to the body Men tend to store fat around the waist and women around the hips and thighs

8. Research/medical facility technique Dual energy X-ray absorptiometry (DEXA) Uses very low-dose beams of X-ray energy Measures total body fat, fat distribution, bone density Techniques to Assess Body Composition: DEXA

9. Hydrostatic Weighing Underwater weighing Most common technique used for decades A person’s “regular” weight is compared with underwater weight Fat is more buoyant than lean tissue Almost all other indirect techniques have been validated against hydrostatic weighing

10. Hydrostatic Weighing

11. Air Displacement • Individual sits inside small chamber (Bod Pod) • Computerized pressure sensors determine the amount of air displaced by the person • Body volume is calculated by subtracting the air volume with the person inside the chamber from the volume of the empty chamber (air in the lungs is taken into consideration) • Body density and percent body fat are then calculated from the body volume • Less cumbersome to administer • Takes only about 5 minutes

12. The Bod Pod, used for assessment of body composition

13. Skinfold Thickness • Based on the principle that the amount of fat beneath the skin is proportional to total body fat • Reliable measurements of this tissue give a good indication of percent body fat • Skinfold test is done with pressure calipers • Several sites are measured and percent fat is estimated from the sum of the three sites using Tables 4.1 (women) and 4.2 or 4.3 (men) • All measurements should be taken on the right side of the body

14. Anatomical landmarks for skinfold measurement

15. Skinfold Thickness

16. Procedure for body fat assessment using skinfold thickness technique

17. Bioelectrical Impedance • Simpler to administer, but accuracy is questionable • Sensors are applied to the skin and a weak electrical current is run through the body to estimate body fat, lean body mass, and body water • Based on the principle that fat tissue is a less-efficient conductor of an electrical current • The easier the conductance, the leaner the individual • Body weight scales with special sensors on the surface may also be used to perform this procedure

18. Body Mass Index (BMI) • Incorporates height and weight to estimate critical fat values at which disease risk increases • BMI = Body Weight (lbs) x 705 ÷ (height in inches)2 • Example • Body Weight = 172 lbs Height = 67 inches • BMI = 172 x 705 ÷ (67)2 • BMI = 27

19. Determination of Body Mass Index (BMI)

20. Mortality risk vs. BMI • BMI is used almost exclusively to determine health risks and mortality rates associated with excessive body weight • Data indicates that disease risk starts to increase when BMI exceeds 25 • The risk also increases for individuals who are underweight (below 18.5)

21. Overweight & obesity trends in the United States, 1960-2000

22. Disease Risk According to Body Mass Index (BMI) BMI does not differentiate fat from lean body mass or note where most of the fat is located Athletes with large amounts of muscle mass can fall into the moderate or high-risk categories

23. Determining Recommended Body Weight Some evidence indicates the mortality rate for underweight people is high The body fat of a healthy thin person is near the high physical fitness standard Underweight people have extremely low body fat, compromising essential fat Normal physiological functions can be impaired if people fall below the essential fat standards of 3% for men and 12% for women

24. Because of the typical reduction in physical activity, each year the average person gains 1-2 lbs of body fat and loses a half a pound of lean tissue Typical body composition changes for adults in the United States

25. Loss of lean body mass can be offset or eliminated by combining a sensible diet with physical exercise Effects of a 6-week aerobics exercise program on body composition