Because methods of assessing body composition can influence how individuals feel about their body (possibly encouraging eating-disordered behaviour), it is essential that precise tools be used to measure body composition and that an expert well versed in body composition read the results. Research locales use numerous methods of body composition: underwater weighing, dual-energy X-ray absorptiometry (DEXA), bioelectrical impedance analysis (BIA), skinfold callipers, air displacement plethysmodraphy (Body Pod), dilution techniques, magnetic resonance imaging (MRI), near-infrared interactance, and magnetic resonance spectroscopy (MRS). These different methods vary in the body constituents measured, which may take account of fat-free mass, fat, bone mineral content, ectopic fat depots, etc. Field procedures generally used comprise skinfolds, body mass index (BMI), and bioelectrical impedance analysis (BIA), because these apparatuses are most convenient. Individuals with admittance to professional training facilities may also have their body composition assessed by more exact methods ordinarily used in research settings, such as those listed above.
That said, field methods for evaluating body composition are those that are handy and easy to use for assessment of numerous people in a short time period. Body mass index is a modest calculation: weight (in kilograms) divided by height in metres (squared). The subsequent number classifies the individual as underweight, normal weight, overweight, or obese. It is a suitable way to quantify obesity rates in a population but should not be used by itself to tag an individual. The problem is that it does not measure actual body composition or differentiate between fat and muscle tissue. Since muscle has larger density than fat and weighs more than fat per volume of tissue, BMI is likely to overvalue body fat levels in muscular individuals, whilst also overestimating body fat in individuals with large body frames. Skin callipers (a tool for determining skinfold width, which can then be used to estimate body fat) are frequently used for a better result. This tool takes measures by clutching a fold of skin at several sites on the body, with the thumb and forefingers dragging the fold away from the underlying muscle, then pinching it with the calliper and noting the reading within two seconds. It is easy to use (once the individual is proficient in the practice), does not necessitate much time, and is non-invasive and cheap. It should be noted though, that inter-person inconsistency is present, with results being less accurate depending on the quality of the callipers. Moreover, different sites may be used and the equations possible total over 100, thereby leading to potential errors in validity, reliability, or both.
Bioelectrical impedance consists of a way of assessing body composition via evaluating the course of a small electrical current through the body. This determines total body water, which can then be used to define total fat free mass (and indirectly, fat mass). It cannot perfectly measure short-term fluctuations in body composition nor can it precisely measure body composition in obese individuals (in whom it may undervalue body fat) and very lean individuals (in whom it may overrate body fat). Thus, the best way to measure body fat would probably be those conducted in research settings. However, as this is most often not possible, the best practical method would be either skinfold callipers, or bioelectrical impedance analysis, though all methods have their inaccuracies.
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- Campbell, Bill I., and Marie A. Spano. NSCA’s Guide to Sport and Exercise Nutrition. Champaign, IL: Human Kinetics, 2011.