Whole-Body Air-Displacement Plethysmography
Whole-Body Air-Displacement Plethysmography is a method for assessing body fat and lean mass, commonly using the BodPod machine. The method is similar underwater (hydrostatic) weighing, but uses air instead of water.
purpose: using air displacement technology for measuring and tracking body fat and lean mass.
equipment required: BodPod by Life Measurements Instruments, Concord, CA.
pre-test: Explain the test procedures to the subject. Perform screening of health risks and obtain informed consent. Prepare forms and record basic information such as age, height, body weight, gender, test conditions. Check and calibrate the equipment. See more details of pre-test procedures.
procedure: 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.
method: Body 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.
advantages: high level of accuracy, ease-of-use, and fast test time. Compared to underwater weighing, the Bod Pod does not require getting wet, and is well suited for special populations such as children, obese, elderly, and disabled persons.
disadvantages: The BodPod unit is very expensive ($30,000 - $40,000) and only a few facilities have it. Some research or academic institutions may offer tests for a fee.
accuracy: The manufacturers indicate that the general error range of the BOD POD is 1-2% (the same as hydrostatic weighing).
comments: The Bod Pod technology is fundamentally the same as underwater (hydrostatic) weighing, but uses air instead of water.
- Dempster P, Aitkens S: A new air displacement method for the determination of human body composition. Med Sci Sports Exerc 1995, 27:1692-1697.
- McCrory MA, Gomez TD, Bernauer EM, Molé PA: Evaluation of a new air displacement plethysmograph for measuring human body composition. Med Sci Sports Exerc 1995, 27:1686-1691.
- Fields DA, Goran MI, McCrory MA: Body-composition assessment via air-displacement plethysmography in adults and children: a review. Am J Clin Nutr 2002, 75:453-467.
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