Body composition

In physical fitness, body composition is used to describe the percentages of fat, bone, water and muscle in human bodies. Because muscular tissue takes up less space in our body than fat tissue, our body composition, as well as our weight, determines leanness. Two people of same sex and body weight may look completely different from each other because they have a different body composition.

The most accurate estimation of body composition is derived from body density by means of the equation of fractional densities which states that the overall density of a mixture containing more than one substance (each with a different density) can be calculated if the proportion and density of each component substance is known. For determination of body composition the body is often assumed to be composed of 4 basic substances ("four compartment model") with the general form of the equation as follows:

Where: ${\displaystyle Db}$ = overall body density, ${\displaystyle w}$ = proportion of water, ${\displaystyle f}$ = proportion of fat, ${\displaystyle p}$ = proportion of protein, ${\displaystyle m}$ = proportion of mineral, ${\displaystyle Dw}$ = density of water, ${\displaystyle Df}$ = density of fat, ${\displaystyle Dp}$ = density of protein, ${\displaystyle Dm}$ = density of mineral

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