Define Body Composition Assessment Methods - Underwater Weighing?

Underwater weighing or hydrostatic weighing is one of the most common body composition methods used in laboratory settings. It is based on densitometry i. e, the measurement of total body density (Db) and the estimation of body composition from Db. Db is the ratio of body mass to body volume (BV); BV is measured by either water displacement or air displacement. The water displacement method, known as hydro densitometry or hydrostatic weighing, has been considered as a gold standard method because it gives a relatively small technical error in the measurement of body density.

To measure body density, a pool and measuring equipment is needed. The subject is weighed in air, and then immersed in water. The difference in the upthrust displacement by water is measured. Thus, the values of total body mass; underwater weight, water temperature and residual lung volume (RV) are measured.

This method is based on Archimedes's principle which states that a submerged object is buoyed up by a force equal to the volume of the water it displaces.  This buoyant force causes the object to weigh less underwater than it does on land.  Me difference between land weight and underwater weight is used to calculate body volume and subsequently body density. Once the body density is measured, this value must be converted into body fat percentage using Siri. Equation (discussed above with 2-C model). Hydrostatic weighing or underwater weighing requires considerable subject cooperation given that multiple trials need to be performed in order to obtain an accurate estimate of underwater weight. Let us get to know about these requirements.