The body is composed of water, protein, fat, and minerals. Methods that determine body composition essentially estimate body fat and lean body mass. Because body fat is the most variable constituent in the body, there are several methods available to help estimate the total amount of body fat (essential fat and stored fat) in relation to fat free mass (muscles, bones, ligaments, tendons, and internal organs). There are two indexes, widely used by industry professionals, to help estimate body composition: the BMI (Body Mass Index) and the FFMI (Fat Free Mass Index). Unlike the BMI, which compares height to weight, the FFMI takes into account the amount of muscle mass a person has and instead, relates that to his/her height.
In the fitness industry, the most common method of determining body composition is a measurement caliper, which measures the thickness of subcutaneous fat in various places on the body. Another method is BIA (bioelectrical impedance analysis or impedance machine), which uses the resistance of electrical flow through the body to estimate body fat.
A more accurate method of determining body fat is the usage of a Body Fat Hydrostatic Water Tank. This method basically configures the body’s buoyancy capability and determines muscle mass accordingly.
A newer form of measuring body composition is called ADP (air displacement plethysmography). Air-displacement plethysmography is a non-invasive procedure that requires very little technical expertise, as opposed to the procedures required for hydrostatic weighing. ADP requires a single fiberglass unit composed of two chambers. The test chamber accommodates the subject during testing and the reference chamber contains instrumentation for measuring changes in pressure between the two chambers. The volume of the test chamber is determined by pressure changes precipitated between the test chamber and reference chamber by a moving diaphragm mounted on the common wall between the chambers. The pressure ratio relationships between the chambers are inversely related and are characterized by Boyle’s Law. Boyle’s Law (named after physicist Robert Boyle) describes the inversely proportional relationship between the absolute pressure and volume of a gas, if the temperature is kept constant within a closed system.
Body Composition is also estimated by using cross-sectional imaging methods, such as MRI (magnetic resonance imaging) and CT (computed tomography). Since MRI and CT give the most precise body composition measures to date, many pharmaceutical companies utilize them to estimate body composition before and after drug therapy, especially in drugs that might effect a patient’s body composition.