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We've learned that losing fat is more important than shedding pounds, so many of us are signing up to get our body fat tested.

But how can we tell if we're getting good tests?Take this advice from certified personal trainers Matt Blake, Mitch Bowers and Dee Tidwell, and researchers Bob Oppliger of the University of Iowa and Stephen Farrell of the Cooper Institute of Aerobic Research:

- Underwater (hydrostatic) weighing:

The most accurate of all body-fat tests, it's based on the theory that fat tissue is lighter than water. Or, the more fat a person has, the less he weighs underwater.

There are a number of questions, however, that need to be asked if you select this test, most often done at some health clubs and at universities. Expect to pay $35 or more. And to get best results you should know:

- Have you blown all the air out of your lungs? Have you smoothed the bubbles out of your swimsuit and hair? Did you empty your bladder before the test? Did you avoid eating anything that could cause excessive amounts ofintestinal gas? All can skew the results.

- If the test is being done in a swimming pool, are you the only person in the pool? If others are swimming, their waves will interfere with the scale.

- Do you get frightened by the idea of staying underwater or emptying your lungs in the water? If so, this may not be the option for you. Between 10 percent and 20 percent of people who try it find it difficult.

- Skinfold caliper test:

Nearly as accurate as underwater weighing, it's also convenient. Get it done at most health clubs, YMCAs and recreation centers. Some hospital wellness programs include caliper tests as part of general health assessments. Expect to pay about $25.

- How qualified is your tester? How much experience has she had? Does he have a four-year degree in exercise physiology or a related field? Is she a certified personal trainer? Caliper tests are only as good as the person administering them. Be especially careful at health fairs where untrained volunteers may be doing the tests.

- How many sites are being measured? You'll need a minimum of three and a maximum of six or seven. That's because people carry their fat in different places. If you measure only lean spots, for example, the results will be artificially low. Most common test sites are the front of the thigh, the back of the upper arm and an inch above the hip bone.

- Have you just worked out? Calipers are more accurate when used on cold muscles.

- If you're getting a follow-up test to measure progress, is the same person doing it each time? Testers vary slightly in how they take the test, so for the sake of continuity, have the same person do your test each time.

- Bioimpedance scales:

They pass a weak electrical current through the body and measure it on the way back out. The theory is that the signal travels faster through the water in lean tissue than through fat. Experts view this as the least accurate method because results can vary up to 10 percent depending on skin temperature and hydration.

You'll probably have to buy your own scale if you want bioimpedance testing. The American Heart Association used to offer public tests, but most chapters have since quit using them at public functions.

- Have you just eaten? Do you have a full bladder? Are you in the water-retaining stage of your menstrual cycle? Do you have saline-filled breast implants? The fluid from any of these sources will skew test results.

- Have you recently worked out vigorously enough to sweat? Have you had coffee or alcoholic beverages in the past 12 hours? Each will have temporarily dehydrated you, which means your fat content will read higher than it really is.

- Has the tester entered the right formula for you? The machine should include different formulas for men and women, adults and children, athletes and sedentary people.