Body Composition Measured By Biolectrical Impedance
A person’s body weight is made up of a range of different components. The term to describe this is body composition. One part of this composition is lean tissue (muscle, bone and organs), and these are metabolically active. The other tissue is adipose or fat, which has no role in metabolism. Most bathroom scales will give a person the total weight of these two parts added together, but do not show the ratio of lean to fat in that weight. Standing on a scale can only tell you whether or not you are heavier than someone else, but it won’t tell you whether you have a lot of fat or a lot of muscle. This leads to some people who have a very high level of muscle weight as being classed as overweight, even if they only have a very low percentage of actual body fat. Particularly for athletes, a standard weight chart is not applicable.
There are a number of methods used to truly measure the actual percentage of body fat versus lean mass. Bio impedance analysis is one such method, but there are others as well. For instance, underwater weighing. Here, a person is weighed while submerged in water. This is based on the Archimedes Principle of displacement. According to this principle, the density of fat and fat free masses are constant. Lean tissue is denser than water and fat tissue is less dense and more buoyant. This method has long been seen as the best way of measuring composition, but new methods have been developed that are potentially even better. Due to the fact that this method is also highly complicated and cumbersome, most physicians prefer to use a skin fold measurement, which is up to 98% accurate if done by a trained professional.
A new way of measuring composition was hence necessary. This lead to the development of bioelectrical impedance. A very low level and safe current is sent through the body. The fat and fat free masses can be calculated due to the fact that current travels through tissues at different rates. It is now possible to have digital scales at home that use this method. A current passes through muscle tissue (which is high in fluids) with great ease, but it is much slower in travelling through fat tissue. Impedance describes what the level of resistance from fat tissue is. The scales then calculate the body fat percentage by adding a person’s gender, height and overall weight measurements. These measurements are very accurate and are now becoming far more common. In fact, it is likely that underwater weighing will soon disappear altogether.