Body Fat Percent Scales With Electrodes

Bioelectrical impedance analysis, or BIA, uses the water in your body to estimate your body-fat percentage. BIA scales contain electrodes that send a small current through your body. This method of body-fat measurement has several advantages over other measuring methods, as well as some disadvantages.

Bioelectrical Impedance

Bioelectrical impedance scales use electrodes that either are built-in to the handgrips and footpads or are external to the scale and stuck to your skin. Scales used in homes usually have built-in electrodes and are less expensive than those with external electrodes. Body fat does not contain much water, making it a bad conductor of electricity. Your fat-free bodyweight, including muscle, contains more water than body fat. A BIA scale sends a low-voltage current through your body. The body fat impedes the signal from the BIA scale. A BIA scale estimates your body fat based on how quickly and easily the voltage runs through your body.

Effectiveness

Several factors affect the accuracy of a bioelectrical impedance scale. If you are dehydrated, the signal does not run through your body as easily. The scale reads this as impedance and may overestimate your body-fat percentage. You should not eat or drink within 4 hours of the test or exercise within 12 hours. Do not consume caffeine or any other diuretic within 1 week of the test. If you follow the procedure correctly, a BIA scale has a margin of error of plus-or-minus 3 percent.

Advantages

Bioimpedance machines are more convenient to use than other machines. Hydrostatic weighing, air displacement and dual X-ray absorptiometry methods all require large, expensive pieces of technologically advanced equipment to measure body fat. BIA machines are quick and painless. You do not feel the low-current voltage that passes through your body. Hydrostatic weighing requires you to be dumped in a water tank and exhale all the air from your lungs, which can be very difficult.

Disadvantages

The accuracy of a bioelectrical impedance scale depends largely on your actions prior to the test. If you workout or drink caffeine right before the test, the results will be skewed. If the subject is unaware of the factors that affect the test, she is likely to receive unreliable results. BIA body-fat testing is most accurate for those with healthy body-fat levels. This method of testing tends to overestimate very lean individuals and underestimate obese individuals.