Which method uses water to assess body fat percentage?

• A. Skin calipers
• B. Bioelectrical impedance monitors
• C. Hydrostatic weighing
• D. 3D body scan

Answer: (C)

Hydrostatic weighing uses water to assess body fat. It relies on Archimedes’ principle: when a person is submerged, they displace a volume of water equal to their body volume. By comparing a person’s land weight with their underwater weight, you can calculate body density (mass divided by volume). Since fat tissue is less dense than lean tissue, you convert that density into percent fat using a formula such as Siri or Brozek. This method was historically considered very accurate, though it requires special underwater weighing equipment and can be influenced by factors like residual air in the lungs and hydration. The other methods don’t involve water: skinfold measurements estimate subcutaneous fat by pinch thickness, bioelectrical impedance gauges body composition from how easily a small electrical current travels through the body, and a 3D body scan uses surface measurements to estimate fat and lean tissues.