Bioimpedance analysis is a procedure using an instrument that is capable of automatically measuring body composition. By then entering the data on body weight and fat mass into a special formula that corrects the Quetelet index with the data on body fat, it is possible to obtain the so-called metabolic index.

How bioimpedance analysis works

  The instrument to be used is called a bioimpedance meter, and consists of two small electrodes. To use it, one of them must be attached to the right ankle and the other to the left wrist (or vice versa). The measurement should be performed with the athlete to be examined lying supine (‘on the stomach’). The bio-impedance meter will pass an imperceptible electric current from one electrode to the other, through the body, and measure the time it takes for the charge to travel the distance. Now, since the human body is essentially made up of only three ‘elements’ (cells, fat and water), and since the electric current takes a different amount of time to pass through each of them, the instrument is able to return the percentage value of each.

The bioimpedance meter

  On the market, there are very cheap bioimpedance tests on the market, as well as extremely expensive ones., for professional instruments. There are also so-called impedancescales, i.e. instruments that, in measuring weight, also detect fat mass and, as I said before, possibly also cell and water mass. In this case, the electrodes are placed in the area where the feet rest. Some believe that impedance scales are less reliable than classical bioimpedance meters, as the latter take their measurements while standing in a decubitus position (lying down). Standing, in fact, implies that part of the water inside the body, due to the action of gravity, moves downwards, invalidating, at least partially, the result.

The metabolic index

  The Quetelet index, as we have already seen, gives an indication of weight in relation to height, but does not distinguish between the various body components. Well, Di Pasquale’s metabolic index (MIDx) makes it possible to correct this indication with the data, obtainable through bioimpedance analysis, on the percentage of fat mass. The formula for the calculation is:

The higher the metabolic index, the leaner and more muscular you are; the lower it is, the fatter and fatter you are.