Body Composition

1. Body Composition

2. Objectives • Define body composition and explain its relationship to body weight. • Calculate your BMI and classify yourself as underweight, normal, overweight, or obese. • Know what a healthy range is for body-fat percentage, as well as the health consequences of having too much or too little body fat. (continued)

3. Objectives (continued) • Explain the various methods of body composition assessment and identify each as a laboratory-based or field technique. • Calculate your ideal body weight using information from your body composition assessment. • Describe recommended strategies for losing and gaining weight.

4. Quantity Versus Quality • A scale provides the quantity but tells nothing about the quality of the body weight. • Although two people can have exactly the same height and weight, the quality of their bodies can be very different. • Body composition focuses on quality.

5. Body Composition Defined • Body composition refers to the components of the human body and their proportions. • It reflects the relative amounts of fat and fat-free mass in the body. • It is one of the health-related components of fitness.

6. Fat and Fat-Free Components • Fat-free mass includes everything other than fat. • Fat mass can be grouped into two categories: • Essential fat—crucial for normal body functioning • Men: estimated to be 3% • Women: estimated to be 12% • Nonessential fat—storage fat for energy, protection, and insulation • Percent body fat: Total body fat is usually expressed relative to body weight.

7. Measuring Body Composition • Height–weight charts • BMI • Body weight (kg) / height squared (m2) • Not the same as body-fat percentage • Predictor of early mortality • Waist circumference • Measurement at narrowest part of torso • Android obesity • Gynoid obesity

8. Risk of Premature Death Increasesas BMI Increases

9. Health Consequences of Overweight • Cardiovascular and coronary heart disease • Hypertension • High cholesterol • Diabetes and blood sugar problems • Certain types of cancers • Arthritis • Menstrual irregularities

10. Health Consequences of Underweight • Malnourishment • Fluid and electrolyte imbalances • Weak bones and osteoporosis • Muscle wasting • Kidney disorders • Reproductive disorders • Sudden death

11. Lab Methods of Body Composition Assessment • Hydrodensitometry • Air-displacement plethysmography (Bod Pod) • Dual-energy X-ray absorptiometry (DXA)

12. Field Methods of Body Composition Assessment • Skinfold method • Bioelectrical impedance analysis (BIA) • Near-infrared interactance (NIR)

13. Hydrodensitometry • Also known as underwater weighing. • Based on Archimedes’ principle. • Muscle sinks and fat floats. • Measures body volume. • Subsequent measurements: • Body density = body mass / body volume. • % body fat = (4.95 / body density) – 4.50. • A measure of residual lung volume is needed for greatest accuracy.

14. Air-Displacement Plethysmography • The Bod Pod is used to get this measure. • Body volume is measured by air displacement instead of water displacement. • This method is quicker and easier than hydrodensitometry. • To get an accurate result, the subject must wear tight-fitting clothing.

15. The Bod Pod

16. Dual-Energy X-Ray Absorptiometry (DXA) • This method uses a low-radiation X-ray to identify underlying tissue. • It measures bone mineral content and bone density as well as fat and lean tissue. • It is capable of taking regional assessments (e.g., trunk versus periphery). • It is easy for the participant. • It is costly and requires an X-ray technician.

17. DXA Method: Full-Body Scan

18. Skinfold Method • Measures folded skin and the fat trapped in the fold. • Assumes a relationship between subcutaneous fat and total body fat. • The technician needs to be skilled: • Proper site location • Pinching technique • Equation selection • Not recommended for obese participants.

19. Skinfold Measures Fatand Layers of Skin

20. Bioelectrical Impedance Analysis (BIA) • A low-level electrical current is passed through the body, and the flow of current is measured. • Water and electrolytes are primarily in the fat-free tissue (good conductor). • Resistance comes from fat (poor conductor). • Measures total body water, fat-free mass, and body fat. (continued)

21. Bioelectrical Impedance Analysis (BIA) (continued) • BIA is more comfortable than skinfold measurements for the participant and requires less skill from the technician. • It requires adhering to pretesting hydration guidelines. • This method is recommended over skinfolds for obese people. • Inexpensive home-use analyzers are available.

22. Near-Infrared Interactance (NIR) • NIR uses an infrared light and reads the amount of light reflected to determine the composition of underlying tissue. • NIR is rapid and painless for the participant and is easy for the technician to administer. • Accuracy is questionable.

23. Determining Ideal Body Weight • To find your current body-fat percentage, have your body composition measured by a trained technician. • Set a reasonable goal. Men should have 5% to 25% body fat; women, 15% to 35%. • To determine your target body weight, divide your fat-free mass by the percent of fat-free mass that you would like to have.

24. Reducing Body Fat • A body fat reduction plan should allow you to retain or gain muscle. • Weight loss should be gradual: 1 or 2 lb (.5 or 1 kg) per week.

25. Gaining Weight • The goal should be to gain muscle mass rather than fat mass. This is achieved by lifting weights. • Eat ample calories, about 400 to 500 more calories per day than your body needs.