In this article, you’ll learn about Hydrostatic weighing and how to check body fat with hydrostatic weighing. Hydrostatic weighing, which is also called underwater weighing, is considered the benchmark for measuring body composition. When compared with cadaver assessments, there is only a 1.5 to 2.0% margin of error. Most of the other methods of measuring body composition are based on formulas derived from underwater weighing research. The concept behind hydrostatic weighing is based on the Archimedes Principle, which provides the following equation:
This technique originally measured the amount of water displaced when a pers« was completely submerged and exhaled all available air from the lungs [leaving only the residual volume (RV) and a small volume of air in the gastrointestinal tract]. Fat tissue is less dense than lean tissue and displaces more water despite weighing less. The body is weighed on an underwater scale. As water buoyancy (i.e.‚ the counterforce of water) reduces body weight significantly, and air and fat mass increase buoyancy, their respective contributions to underwater weight have to be determined. To minimize errors with this protocol, the RV should be measured in water. This volume can be 100 to 200 mL lower underwater due to the non-compressible nature of water that helps compact the Iungs. Given the costs, equipment, and expertise needed to accurately measure RV, mathematical calculations are often used to estimate RV, which may introduce a margin of error of 300 to 400 mL. For every 100 mL error in the estimation of RV, the percent body1 error changes by 0.7%.
Hydrostatic weighing is not a practical approach for the standard fitness center. The apparatus is expensive and takes up a lot of room, testing takes a considerable amount of time and expertise, and many people feel uncomfortable remaining submerged underwater after they have exhaled all available air from their Iungs. This evaluation t is often found in elite clinical settings and in many colleges and universities.
Where to Get a Hydrostatic Underwater Weighing Test
Many universities offer hydrostatic weight tests and several companies offer testing for the public. Some, such as Body Fat Test provides mobile hydrostatic body composition testing service. The lack of easy access to this testing makes is less than ideal to use, especially since bioelectric impedance measurement is now widely available.