What is Air Displacement Plethysmography (the Bod Pod) and how does it work?
What is Air Displacement Plethysmography (the Bod Pod) and how does it work?
Overview
Air Displacement Plethysmography (ADP), commonly known as the Bod Pod, is a body composition assessment method that uses air displacement — rather than water — to calculate body volume and density. Like hydrostatic weighing, it is primarily used in research and clinical settings.
Important: ADP is also an indirect measurement. Body density must be calculated before body composition can be estimated.
How It Works
The formula:
Body Density = Mass ÷ Volume
During the assessment:
- The client's mass (weight) is measured directly.
- The client sits inside a sealed, egg-shaped chamber (the Bod Pod).
- The system measures the volume of air in the chamber when empty.
- It then measures the volume of air remaining when the client is seated inside.
- The client's body volume is calculated by subtracting the occupied air volume from the empty chamber volume.
- Body density is derived and used to estimate body composition.
How ADP Compares to Hydrostatic Weighing
Feature | Hydrostatic Weighing | ADP (Bod Pod)
Displacement medium | Water | Air
Client gets wet | Yes | No
Measurement type | Indirect | Indirect
Typical results | Similar | Similar
Setting | Research/clinical | Research/clinical
Both methods produce comparable results. The most practical difference, as noted in training materials: "whether or not you get wet."
Notes
- The same pre-assessment protocols apply as with hydrostatic weighing: avoid eating, drinking, and exercising beforehand, as these can affect reliability.
- Always use consistent assessment procedures across sessions for the same client.
- Cost and space requirements limit ADP use primarily to research or clinical environments.
If this resolves your issue, no further action is needed.
If the problem persists, contact support and include: the assessment protocol used and any pre-assessment conditions that may have varied.
Applies to: Styku body composition education resources; Health Tech Assessment curriculum, Lesson 9