Bioelectrical Impedance Analysis (BIA) The
BIA technique works by sending a small electrical current through the body and measuring the body’s resistance to it. Fat-free tissues, where most body water is located, are good conductors of electrical current, whereas fat is not (see the box “Using BIA at Home”). Thus, the amount of resistance to electrical current is related to the amount of fat-free tissue in the body (the lower the resistance, the greater the fat-free mass) and can be used to estimate percent body fat.
Bioelectrical impedance analysis has an error rate of about ±4-5%. To reduce error, follow the manufacturer’s instructions carefully and avoid overhydration or underhydration (more or less body water than normal). Because measurement varies with the type of BIA analyzer, use the same instrument to compare measurements over time.
Advanced Techniques: DEXA and TOBEC Dualenergy X-ray absorptiometry (DEXA) works by measuring the tissue absorption of high- and low-energy X-ray beams.
Taking skinfold measurements with calipers.
Using bioelectrical impedance analysis to estimate percent body fat.
Using BIA at Home
Scientists can use several techniques to accurately measure body composition. As described in the chapter, these techniques include underwater weighing, air displacement, and Dual-energy X-ray absorptiometry (DEXA). These methods, however, are costly and require technical expertise.
Bioelectrical Impedance Analysis BIA The Photo Gallery
You can estimate your body fat and fat-free weight simply and accurately, at home, without the help of a technician. All you need is a digital home scale with a built-in bioelectrical impedance analyzer (BIA) or a hand-held BIA unit. BIA works by measuring the resistance in the body to a small electric current. Electricity flows more slowly through fat tissue than through muscle, so the more fat you have, the more slowly such a current will flow through your body. Conversely, a current will pass through your body more quickly if you have more fat-free (muscle) weight.
To use a BIA scale or hand-held unit, just stand on the scale with bare feet or grasp the handles with each hand. As it checks your weight, the BIA unit sends a low-voltage electrical current through your body and analyzes the speed at which the current travels. Checking your weight and body composition takes no longer than checking your weight alone. Most BIA units can remember your last weight and body composition measurement, making it easy to compare the measurements from day to day or week to week. Some scales can remember measurements for multiple people, as well. A study of 22 weight-trained men showed that BIA compared favorably to underwater weighing for measuring body composition. Measurements of fat and lean mass are most valuable for measuring changes in body composition during diet and exercise programs.
Popular BIA scales and hand-held BIA devices are manufactured by Taylor, Whynter, Omron,
RemedyT, and Tanita. These scales and devices are available in most department stores and online, and cost between $50 and $200, depending on features.
The procedure has an error rate of about ±2%. Total body electrical conductivity (TOBEC) estimates lean body mass by passing a body through a magnetic field. These methods are often used in sophisticated research projects but are seldom available to the average person. We mention them because they are often used for comparison with some of the field tests described in this chapter.
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