Usage and Features
The basic Tanita scale looks like a standard digital bathroom scale. It is flat, portable and you place it on the floor and step onto with both feet. Turn the scale on and, when prompted, input your sex, age and height using the buttons below the display monitor. Foot placement is indicated by two electrode-containing metal panels. Step on them with bare feet and the display monitor will reveal your body composition within seconds.
All Tanita scales generally function in the same way, but appearance varies among models. Some newer models have transparent electrodes so that the foot panels are not visible. Many of the professional scales feature a display monitor that is elevated on a column--a layout similar to a traditional doctor's office scale. The professional models also have a built-in printer that prints the results out on a small piece of paper. Most of the bathroom scales are battery powered, while the professional scales can usually be plugged into an outlet.
How it Works
Tanita scales analyze body composition using bioelectric impedance analysis (BIA). BIA works by sending a small electric current through your body and determining how much resistance the current encounters. The current passes through water easily and has more difficulty passing through other substances. Fat contains little water, so the more fat your body contains, the more the current is impeded. Muscle, on the other hand, has high water content allowing the current to pass through more easily. The Tanita scale can report body weight, body fat percentage, muscle mass, total body water, visceral fat, bone mass and basal metabolic rate, but the only values it actually measures are weight and total body water. It then calculates the other values based on known relationships between body substances. Since the Tanita scale really only measures water, accuracy of the results is highly dependent on how hydrated you are. Having a full bladder or being dehydrated can affect the accuracy of the test. Athletes tend to be less hydrated than non-athletes which can also skew the results. For this reason, Tanita scales often include an "athlete" setting. To get the best results, you should be normally hydrated and perform repeat testing under the same circumstances. For example, always test yourself at the same time of day and, for women, at the same time during your menstrual cycle.
What it Means
Tanita scales have about a 5 percent margin of error when compared to the gold standard tests of body composition; hydrodensitometry and DEXA (dual energy x-ray absorptiometry) testing. However, margin of error is only 1 percent when re-testing the same individual under identical circumstances. Although Tanita scales are not as precise as gold-standard techniques, they are extremely convenient and easy to use. If used correctly, Tanita scales can be an effective tool for monitoring changes in your body composition over time.
References
- Tanita
- "ACSM's Resource Manual for Guidelines for Exercise Testing and Prescription, 5th ed.;" American College of Sports Medicine; 2006
- Tanita: How BIA Works
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