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Nutrition in Physical Activity

Nutrition involves the metabolism of energy in order to produce mass or work. Thus, the endpoint of nutrition is the creation of body cell mass or adipose tissue, chemical, thermal or physical work. Therefore, no discussion of nutrition can be comprehensive without the inclusion of these outcomes. Physical fitness is defined as the ability to perform moderate-to-vigorous levels of physical activity without undue fatigue and the capability of maintaining this capacity throughout life.(Wilmore, 1988) Fitness encompasses a variety of characteristics including cardiorespiratory performance, body composition (including regional fat distribution), muscular strength and endurance, flexibility and balance. (Wilmore, 1988).

Sixty percent of Americans are not engaged in regular physical activity and 25% engage in none at all. Nearly half of Americans 12-21 years of age do not participate in regular physical activity. Physical inactivity is more prevalent among women than men, among African-Americans and Hispanics than whites, among older than younger adults, and among the less affluent than the more affluent.

This section discusses body composition and methods of measurement. The types and recommended quantities of activity for healthy people will be reviewed. General information regarding fueling for activity and sport are provided.

There are numerous methods available for determining body composition. Most commonly, caliper measures are employed. These are reasonably accurate when performed by a skilled clinician using metal (Lange, Harpenden, or Holtain) calipers. Equations are based on testing from 3-9 body sites. Equations are population-specific, i.e., for children, for athletes. This methodology is widely available.

photo of BIA attached to hand of foot of patient

Bioelectrical Impedance Analysis (BIA)

BIA is performed by a trained clinician using a hand held impedance monitor. It requires placement of electrodes on the wrist and ankle. Measures of body cell mass (lean tissue), adipose tissue, intracellular water and extracellular water are reported. It quantifies adipose tissue but does not delineate where it is deposited. Body fat percentage is calculated with a margin of error of 3-4%; fat free mass within 2.5 to 3.5 kg. The equipment is widely available.

Underwater Weighing

Underwater weighing is typically performed in a research setting. The subject is weighed in air and then weighed submerged in water. The availability of the test is very limited and the procedure is time-consuming.

Dual Energy X-ray Absorptiometry (DEXA)

DEXA measures three compartments: total body mineral (from bones), fat-free soft (lean) mass, and adipose (fat) tissue. It can measure the regional disposition as well as the total quantity of adipose. The availability of the test is very limited.

The following chart lists typical body fat percentages by age group. Body fat usually increases with age as muscle mass declines. These changes are slowed but not prevented by a regular, well-rounded activity program. It should be noted that females will have considerably more body fat than similarly fit males of the same age range. Choose gender and age below to find out the percent body fat norm, or go to the entire chart.

Typical Body Fat Percentages by Age Group

While there is wide variability in the body fat of individuals, the following chart lists some ranges for adults of varied ages. In the athletic groups listed, recreational and performance athletes demonstrate a wide range of percent body fat, even within the same sport. Fat percentage usually increases off-season. A degree of leanness conducive to peak performance or speed may not be the same percentage that is compatible with health or aesthetics.

Males (%)
Females (%)
Essential Body Fat
~ 5
~ 8
Minimal Body Fat
~ 5
~ 10-14
Athletic Groups
Fitness and Health

1. Pat Vehrs, PhD, Brigham Young University, Utah


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