Air plethysmography is a non-invasive method used to measure body composition, particularly body fat and lean mass. It works by assessing changes in air pressure within a sealed chamber as a person enters it. The volume of air displaced by the body is calculated, allowing for an accurate estimation of body density. This technique is often used in clinical and research settings to monitor health and fitness. It is considered a reliable alternative to other methods like DEXA scans or underwater weighing, providing valuable information without the need for radiation or water immersion.