National Academy of Sports Medicine (NASM) Certified Sports Nutrition Coach Practice Test

Hydrostatic weighing is based on the two-compartment model of body composition assessment. This model divides body composition into two primary components: fat mass and lean body mass.

In hydrostatic weighing, an individual's body density is measured while they are submerged in water. This method relies on Archimedes' principle, which states that the buoyant force on an object submerged in a fluid is equal to the weight of the fluid displaced by that object. By measuring the weight of a person in air and the weight of the same person underwater, it provides a means to calculate body density. From this density, one can estimate the proportions of fat mass and lean mass based on their respective densities.

Understanding the two-compartment model is essential as it focuses specifically on differentiating between fat mass, which is less dense and therefore contributes less to total body weight in water, and lean body mass, which includes muscle, bones, and water that are denser than fat. This distinction is vital for assessing overall health and fitness, making hydrostatic weighing a valuable tool in sports nutrition and body composition assessment.