Air Displacement
The Bod Pod system measures body composition by determining body volume and body weight. The subject should not have exercises for the previous two hours, as they must be fully rested and hydration status and increases in muscle temperature can adversely affect the results. Body weight is measured using scales. Body volume is measured by first measuring the volume of the chamber while empty. Then the volume of the subject chamber is measured with the subject inside. By subtraction, the volume of the subject is determined. Once those body volume and weight are determined, body density can be computed and inserted into an equation to provide percent fat measurements.
Volume is determined by monitoring changes in pressure within a closed chamber. These pressure changes are achieved by oscillating a speaker mounted between the front testing chamber and a rear reference chamber, which causes complementary pressure changes in each chamber. The pressure changes are very small and are not noticed by the individual being tested.
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