In physical fitness, body composition is used to describe the percentages of fat, bone and muscle in human bodies. The percentages of fat (body fat percent) is of most interests because it can be very helpful in judging health in addition to body weight.
In average, a healthy male's body should have 12~18 percent fat. In females the number is slightly higher; approximately 14~ 20 percent fat.
Body composition (particularly body fat percentage) can be measured in several ways. The most common method is by using a set of measurement calipers to measure the thickness of subcutaneous fat in multiple places on the body. This includes the abdominal area, the subscapular region, arms, buttocks and thighs. These measurements are then used to estimate total body fat with a margin of error of approximately four percentage points.
Another method is Bioelectrical impedance analysis (BIA), which uses the resistance of electrical flow through the body to estimate body fat.
A more accurate but less convenient method is using a large tank of water to measure body buoyancy. Increased body fat will result in greater buoyancy, while greater muscle mass will result in a tendency to sink.
Much recently, Body Composition is being estimated using cross-sectional imaging methods like Magnetic Resonance Imaging (MRI) and Computed Tomography (CT). Since MRI and CT give the most precise body composition measures to-date, many pharmaceutical companies are very interested in this new procedure to estimate body composition measures before and after drug therapy especially in drugs that might change body composition. Image Reading Center at the New York obesity reseach center in Manhattan is the only expert facility that utilizes DEXA, MRI and CT in Body Composition estimation for large research studies and pharmaceutical clinical trials.
A new technique for measuring body composition has been developed using the same principles as under water weighing. The technique uses air, as opposed to water, and is known as air displacement plethysmography (ADP). Subjects enter a sealed chamber that measures their body volume through the displacement of air in the chamber. Body volume is combined with body weight (mass) in order to determine body density. The technique then estimates the percentage of body fat and lean body mass through known equations (for the density of fat and fat free mass).
ADP is quickly becomming the preferred method for measuring human body composition in medical, research, athletic, military, and health club environments, due to the speed, accuracy, and safety of the technique.