Hydrostatic weighing
Encyclopedia
Hydrostatic weighing is a method for measuring the mass density of a body.
, using the following three measurable values: The weight of the body outside the water, the weight of the completely-immersed body (a weight that may be negative if the body in question is less dense than water) and the density of the water:
Multiplying by the density of water gives
.
and percentage body fat may be estimated. This is occasionally used for assessment of obesity
. The residual volume in the lungs can add error if not measured directly. Hydrostatic weights gives body density, and percent body fat can be estimated using the Siri or Brozek formula.
Method
The following method has the advantage of needing no volume information of the body (see the note about the residual volume below). The procedure is based on Archimedes' principleArchimedes' principle
Archimedes' principle relates buoyancy to displacement. It is named after its discoverer, Archimedes of Syracuse.-Principle:Archimedes' treatise On floating bodies, proposition 5, states that...
, using the following three measurable values: The weight of the body outside the water, the weight of the completely-immersed body (a weight that may be negative if the body in question is less dense than water) and the density of the water:
Multiplying by the density of water gives
.Application
From this density information body compositionBody composition
In physical fitness, body composition is used to describe the percentages of fat, bone and muscle in human bodies. Because muscular tissue takes up less space in our body than fat tissue, our body composition, as well as our weight, determines leanness...
and percentage body fat may be estimated. This is occasionally used for assessment of obesity
Obesity
Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health, leading to reduced life expectancy and/or increased health problems...
. The residual volume in the lungs can add error if not measured directly. Hydrostatic weights gives body density, and percent body fat can be estimated using the Siri or Brozek formula.
See also
- Body compositionBody compositionIn physical fitness, body composition is used to describe the percentages of fat, bone and muscle in human bodies. Because muscular tissue takes up less space in our body than fat tissue, our body composition, as well as our weight, determines leanness...
- Composition of the human bodyComposition of the human bodyThe composition of the human body can be looked at from several different points of view.By mass, human cells consist of 65–90% water . Oxygen therefore contributes a majority of a human body's mass...