Body fat measurement by air displacement plethysmography: Theory, practice, procedures, and applications

Abstract

The importance of measuring body composition has increased because of the need to evaluate changes in nutritional status that can affect body reserves differentially. These changes can be detected only by using valid body composition measurement techniques. Air displacement plethysmography (ADP) has proved to be a valid method for determining body composition in adults and children. ADP measures body volume using a subtraction technique in which body volume equals reduction in the volume of a chamber resulting from the introduction of the individual into the chamber. There are two versions of the plethysmograph, one for adults and children, the BOD POD, and another version for infants, the PEA POD. Both versions correct the raw body volume measurement for the isothermal effect of skin on air and thoracic gas volume. The body volume is then converted to mass and density relationships for body fat and fat-free masses, and body fat percentage is calculated. In both formats, ADP has good reliability in terms of body volume and fat percentage and has been validated against three-compartment (3C) and four-compartment (4C) models. It has also been used to develop body composition prediction equations for methods like bioimpedance analysis (BIA) and anthropometry in a wide range of populations. Among other applications, ADP has been applied successfully to determine the relationship between body size and adiposity, to evaluate intervention programs based on diet or physical activity, and in athletes, to evaluate body composition changes related to training in different sports.