Final answer:
Air displacement plethysmography or Bod Pod measures the two main components of body composition: fat mass and lean mass by estimating body density using changes in air pressure.
Step-by-step explanation:
Air displacement plethysmography, often recognized by the brand name Bod Pod, measures the body composition, specifically by determining the body's fat and lean mass. This technique uses changes in air pressure within the chamber to determine the volume of the person inside it. By measuring a person's mass and volume, the Bod Pod calculates body density and, in turn, body composition.
Body composition, as determined by the Bod Pod, is a two-component model which quantifies the amounts of fat mass and lean mass. Fat mass refers to all the body's fat tissue, while lean mass encompasses the weight of muscles, bones, organs, and other non-fat tissues. This method is particularly useful as it provides quick, noninvasive measurements and is a suitable alternative to underwater weighing and other traditional methods like the skin-fold test or bioelectrical impedance analysis (BIA).