Body Composition

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)

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.

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.

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.

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.

Measuring Body Composition Height–weight charts BMI –Body weight (kg) / height squared (m 2 ) –Not the same as body-fat percentage –Predictor of early mortality Waist circumference –Measurement at narrowest part of torso –Android obesity –Gynoid obesity

Risk of Premature Death Increases as BMI Increases

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

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

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

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

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) – A measure of residual lung volume is needed for greatest accuracy.

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.

The Bod Pod

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.

DXA Method: Full-Body Scan

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.

Skinfold Measures Fat and Layers of Skin

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)

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.

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.

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.

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.

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.