exercise physiology 11

Body Composition

Body Build, Size, and Composition

Body build is the form or structure of the body.• Muscularity• Linearity• Fatness

Body size is determined by height and weight.

Body composition refers to the chemical composition of the body• Fat mass• Fat-free mass

Three Models of Body Composition

Adapted, by permission, from J.H. Wilmore, 1992, Body weight and body composition. In Fasting, body weight, and performance in athletes: Disorders of modern society, edited by R. Brownell and J.H. Wilmore (Baltimore, MD: Lippincott, Williams, and Wilkins), 77-93.

Did You Know . . . ?

Fat-free mass is composed of all of the body’s nonfat tissue, including bone, muscle, organs, and connective tissue. Lean body mass includes all fat-free mass along with essential fat. Lean body mass is difficult to measure, so the fat mass/fat-free mass model is most often used.

Did You Know . . . ?

Body composition is a better indicator of fitness than body size and weight. Being overfat (not necessarily overweight) has a negative impact on athletic performance. Standard height–weight tables do not provide accurate estimates of what an athlete should weigh because they do not take into account the composition of the weight. An athlete can be overweight according to those tables yet have very little body fat.

Assessing Body Composition

• Densitometry (hydrostatic weighing)• Skinfold fat thickness• Bioelectric impedance

Densitometry

• Body density = Body mass ÷ Body volume• Body mass = measured on a regular scale• Body volume = measured using hydrostatic

(underwater) weighing accounting for

water density and air trapped in the lungs

• % body fat = (495 ÷ body density) – 450

Underwater Weighing Technique to Determine Density of the Body

Tom Pantages

Dual-Energy X-Ray Absorptiometry Machine

Photo courtesy of Hologic, Inc.

Bod Pod device

Photo courtesy of Life Measurement, Inc.

Measuring Skinfold Fat Thickness at the Triceps Skinfold Site

© Human Kinetics

Bioelectric Impedance Technique for Assessing Relative Body Fat

© Human Kinetics

Did You Know . . . ?

Inaccuracies in densitometry are due to the variation in the density of the fat-free mass from one individual to another. Age, sex, and race affect the density of fat-free mass.

Body Composition and Performance

Maximizing Fat-Free Mass• Desirable for strength, power, and muscular

endurance• Undesirable for endurance or jumping sports if the

result is weight gain

Minimizing Relative Body Fat• Desirable, especially in sports in which the body

weight is moved through space• Improves speed, endurance, balance, agility, and

jumping ability

Relative Body Fat in Elite Female Track and Field Athletes

Data from J.H. Wilmore et al., 1977, “Body physique and composition of the female distance runner,” Annals of the New York Academy of Sciences 301: 764-776.

Risks With Severe Weight Loss

• Dehydration• Chronic fatigue• Disordered eating and eating disorders• Menstrual dysfunction• Bone mineral disorders

Appropriate Weight Guidelines

• Maximize performance within the specific sport • Are based on body composition• Emphasize relative body fat rather than total body mass• Use a range of relative fat values that are considered

acceptable for the athlete’s age and sex

Achieving Optimal Weight

• Combine proper diet with exercise.• Lose no more than 1.0 kg (2 lb) per week.• Reduce caloric intake to 200 to 500 kcal less than daily

energy expenditure.• Use moderate resistance and endurance training.