Article of the Month
Body Composition Testing: No Weigh
By Brad Schoenfeld, CSCS, CPT
How much do you weigh? If you're like the majority of people, you can answer this question in the blink of an eye. Without a doubt, Americans are extremely weight-conscious; on average, they step on the scale almost as frequently as they brush their teeth!
However, scale weight often is a poor indicator of body composition-the percentage of a person's lean tissue (such as muscle) to fat. This is especially true for women. Due to monthly hormonal fluctuations, women are prone to retaining fluids. During the premenstrual period, it is not unusual for a woman to gain five pounds or more of water. Although this is only a temporary phenomenon, it shows up on the scale as extra weight-a fact that can be damaging to the female psyche.
The best way to accurately assess body composition is through bodyfat testing. A bodyfat test measures the actual amount of fat in your body as compared to lean tissue. The significance here is that lean tissue has a much greater density than fat and thus weighs more by volume. For example, a brick and a sponge can have the same dimensions, but the brick will be substantially heavier. Similarly, two women can both be exactly the same height and weight, yet one can wear a size six dress while the other wears a size twelve!
Recently, the medical community established guidelines for "ideal" bodyfat percentages. From a health perspective, a male's body should be comprised of about 12 to 22 percent fat. In females the number is slightly higher; approximately 18 to 28 percent fat.
There are a number of different modalities that can be used measure bodyfat. Of these modalities, three have received universal acceptance: hydrostatic weighing, skinfold testing and bioelectrical impedance. The following are the pros and cons of each:
Hydrostatic Weighing:Hydrostatic weighing is considered the "gold standard" in bodyfat assessment. In this technique, a person is submerged underwater while seated in a chair that is attached to a scale. The person holds her breath for about five seconds and her weight is recorded. The underwater weight is then plugged into a formula that estimates bodyfat percentage.
Unfortunately, the benefits of hydrostatic weighing are largely offset by its inefficiency. The test requires the supervision of highly trained laboratory technicians and can take more than an hour to complete. Because it is so labor intensive, it also is quite expensive. Thus, for most people, hydrostatic weighing is not a viable option.
Skinfold Testing:A popular alternative to underwater weighing is skinfold testing. Skinfold testing is by far the most common method used to measure bodyfat percentage. Here, folds of skin are pinched at various sites on the body and a caliper is used to measure their thickness. The resultant numbers are added together and then compared to a chart that estimates your bodyfat level. When done correctly, this method is almost as precise as underwater weighing and is much more efficient.
However, while the skinfold technique can be useful, it does have several shortcomings. First, measurements are highly dependent on the skills of the practitioner. Even slight variations in calculations can result in large discrepancies in results. Furthermore, since direct physical contact is required, many people are uncomfortable during the procedure, making it inappropriate for general screening purposes.
Bioelectrical Impedance:Perhaps the most efficient testing alternative is bioelectrical impedance. This method measures the speed at which a mild electrical current moves through the body. It is based on the presumption that electricity passes more easily through lean tissue than it does through fat. Since the device used to measure bioelectrical impedance is compact-approximately the size of a transistor radio-it allows testing to be conducted almost anywhere. A person simply grasps the handles of the unit and, within seven seconds, a readout is given.
Generally speaking, the measurements attained from bioelectrical impedance are quite accurate-usually within a few percentage points of hydrostatic weighing (although it tends to overestimate those who are very lean and underestimate those who are very obese). And, because it's fast and non-intimidating, it can be used on all populations and in any environment.
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