What is Ideal Body Composition? by ADA Page 3

Assessment of Body Composition

Methods for assessment of body composition are based on either a 2-component or a multicomponent model and use several different measurement techniques. Two-component models divide the body into either fat mass (all lipids within the body) or fat-free mass (the remainder after fat is subtracted). The multicomponent model divides the body into 3 or more components. For example, the 3-component model divides the body into fat mass and 2 components of fat-free mass (bone mineral and lean tissue). The criterion methods most commonly used to assess components of body composition in athletes are based on a 2-component or a multicomponent model. Though a multicomponent criterion model is preferred for assessing body composition because it provides more accurate estimates, measurement techniques required for this model are not readily available to most athletes. A 2-component criterion model typically uses hydrodensitometry (hydrostatic weighing) or plethysmography (BODPOD) measurement techniques, and a 3-component model uses dual-energy x-ray absorptiometry (DEXA) measurements. The most common methods used to measure body composition in field or clinical settings include anthropometry (skinfolds), bioelectrical impedance analysis (BIA), and near-infrared interactance. These field methods are validated using either 2-component or multicomponent criterion models (35). When using these field methods, care should be taken in choosing the appropriate validated prediction equation for estimating body composition based on an athlete’s demographics (age, sex, level of adiposity, ethnicity, and physical activity) in order to obtain accurate estimates (36).

The relative validity of any body composition field method depends on its accuracy compared with the criterion method and its reliability (reproducibility) (31). DEXA and hydrostatic weighing (hydrodensitometry) are 2 widely used criterion methods from which field methods of body composition assessment for athletes are developed (37-42). Regardless of the method used, athletes and coaches should know the errors associated with the body composition assessment method being used. With carefully applied skinfold or BIA methods, it is possible to estimate relative body fat percentage with an error of 3% to 4%, and to estimate fat-free mass within 2.5 to 3.5 kg (27,31,35). Thus, if the actual body fat percentage is 15%, then predicted values could range from 12% to 18% (assuming a 3% error). If the actual fat-free mass is 50 kg, then predicted values could range from 47.5 to 52.5 kg, assuming an error of 2.5 kg. If inappropriate prediction equations for a method are used, poor measurement techniques applied or if the measurement equipment is poorly maintained and calibrated, the errors associated with the body composition estimate will be much larger. Because of the errors associated with body composition assessment methods, it is inappropriate to set a specific body-fat percentage goal for an individual athlete. Instead, a range of target percentage of body-fat values should be recommended.

CARBOHYDRATES: How Much?; Nutrition and Performance:PART 1; Nutrition For Active Adults PART 2, Energy Needs: PART 3, Body Composition: PART 4, Carbs, Fat, Protein, REFERENCES

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© ADAF 1999. Reproduction of this fact sheet is permitted for educational purposes.

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