Anita Bean's Sports Nutrition for Women by Anita Bean

Author:Anita Bean
Language: eng
Format: epub
Publisher: Bloomsbury Publishing

Bioelectrical impedance

Body composition and body fat analysers and scales available for home use are based on the principle of bioelectrical impedance. These devices determine total weight, the percentage and amount of body fat, muscle mass, water and even bone mass. While the readings can be affected by hydration levels, skin temperature and other factors, if you follow the directions and always take the reading under similar conditions, you will obtain fairly accurate results.

In this method, a mild electrical current passes through the body, either from foot to foot or foot to opposite hand. It relies on the principle that lean tissue is a good conductor of electricity, while body fat creates a higher resistance. In other words, the current moves much more easily and more quickly through lean mass, but much more slowly through fat mass. Thus the amount of current flowing through the body reflects the relative amount of body fat: the more body fat you have, the greater the resistance.

However, this method is less accurate for very lean and very fat people.

Dual energy X-ray absorptiometry (DEXA)

A DEXA scan is the most accurate method for measuring body fat. It is painless and you are not enclosed by the equipment at any stage during the scanning process. The scanner itself consists of a large, flat table, which you lie on during the scan. Beneath the table is an X-ray generator. The DEXA machine sends a thin, invisible beam of very low-dose X-rays from two different sources through the body. The amount of X-rays that come through the tissue from each of the two X-ray sources is measured by a detector. The ratios can then be used to predict total body fat, fat-free mass and total body bone mineral. The denser the tissue is, the fewer X-rays get through to the detector. This information is sent to a computer, which generates an image of the body. The procedure can take about 10–20 minutes.

Unfortunately, due to their cost and size, DEXA machines are not generally accessible to the public. They are used mostly for measuring bone density to diagnose osteoporosis, but are also used in hospital and university research departments for body composition analysis – some offer a body composition analysis for sportspeople.

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