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Learn the factors of accurate body composition assessment

By Dan Benardot


Body composition has become an important part of athlete assessment. The amount of muscle and fat an athlete has can be predictive of performance, and bone mass assessment is important for understanding if developmental problems exist or if the athlete will face current or future risk for fracture. A periodic assessment of body composition also helps the athlete understand if the training regimen is causing the kinds of physical changes that are being sought. However, there are some important things to keep in mind when assessing body composition.

You can alter body composition by changing your diet and exercise, but these two should be considered together when making changes. Making dramatic changes in either direction is likely to cause unpredictable problems in your body composition. If you increase your training regimen, it is necessary to increase your energy intake to support the increase in energy expenditure. Putting yourself in a severe energy-deficit state by increasing exercise and maintaining or lowering energy intake is likely to lower metabolic rate, increase fat storage, and cause a breakdown of muscle to support energy needs. Eating too much is also likely to increase fat storage. It’s best to maintain energy intake throughout the day, so athletes should be careful to consume enough energy to support exercise rather than make up for an energy deficit at the end of the day.

Athletes often compare body composition values with other athletes, but this comparison is not meaningful and may drive an athlete to change body composition in a way that negatively affects both performance and health. Health professionals involved in obtaining body composition data should be sensitive to the confidentiality of this information. They should also explain to each athlete that differences in height, age, and gender are likely to result in differences in body composition, without necessarily any differences in performance. Strategies for achieving privacy and helping the athlete put the information in the proper context include the following:



  • Assess only one athlete at a time to limit the chance that the data will be shared.
  • Give athletes information on body composition using phrases such as “within the desirable range” rather than a raw value, such as saying, “Your body fat level is 18 percent.”
  • Provide athletes with information on how they have changed between assessments rather than offering the current value.
  • Increase the focus on muscle mass, and decrease the focus on body fat.
  • Use body composition values as a means of explaining changes in objectively measured performance outcomes.



Different methods for assessing body composition produce different standard results. Therefore, it is inappropriate to compare the results from one method with the results of another. If athletes are being evaluated to determine body composition change over time (an appropriate use of body composition assessment), this comparison should be made only if the same method has been used for the entire assessment period. For instance, the difference in two DEXA scans taken several months apart provides valuable information on how body composition has changed in an individual, as does the difference in two skinfold assessments. However, the difference between body composition values from a DEXA scan and a skinfold equation is not useful in determining change. Even within methods, the same prediction equations should be used to determine if an athlete’s body composition has changed between measurements.

Most athletes would like their body fat level to be as low as possible. However, athletes often try to seek a body fat level that is arbitrarily low (so low that it has nothing to do with the norms in the sport or their own body fat predisposition), and this can increase the frequency of illness, increase the risk of injury, lengthen the time the athlete needs before returning to training after an injury, reduce performance, and increase the risk of an eating disorder. Body composition values should be thought of as numbers on a continuum that are usual for a sport. If an athlete falls anywhere on that continuum, it is likely that factors other than body composition (e.g., training, skills acquisition) will be the major predictors of performance success.

Seeking arbitrarily low body fat levels or weight is an issue in sports where making weight is a common expectation. Wrestlers in particular make dangerous efforts—sometimes leading to death—to lower body fat levels and weight to be more competitive. Read more about this subject in the section on wrestling in chapter 13.

Athletes who are assessed frequently (weight or skinfold measurements recorded regularly) are fearful of the outcome because the results are often (and inappropriately) used punitively. Real changes in body composition occur slowly, so there is little need to assess athletes every week, every two weeks, or even every month. Assessing body composition two to four times each year is an appropriate frequency to determine and monitor body composition change. In some isolated circumstances when an athlete has been injured or is suffering from a disease, such as malabsorption, fever, diarrhea, or anorexia, it is reasonable for a doctor to recommend a more frequent assessment rate to control for changes in lean mass. Coaches who have traditionally obtained weight or body composition values much more frequently (e.g., weekly, monthly) should shift their focus to a more frequent assessment of objective performance-related measures.

This is an excerpt from Advanced Sports Nutrition.




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