Monday, August 12, 2002

Some fitness tests don't measure up


Body-fat methods can be inaccurate, but low-tech comparisons often valid

By Sarah Anchors
The Arizona Republic

        Step into an LA Fitness center, and you're facing it: body fat. The metal suitcase that looks like a spy apparatus is the Futrex-5000, which measures fat with a near-infrared light wand to the biceps.

        Enter a gym, and one of the first things trainers will do is pinch rolls with calipers, or use the light wand or another type of machine to gauge that body fat.

        Almost every gym offers body-fat measurements, sometimes as part of a free evaluation; other times there's a fee. But health officials warn that the measurements are not always accurate and suggest other ways of measuring fitness progress.

        Water-replacement, done by submerging a person several times in a pool, has long been considered the gold standard of such measuring. DEXA, an X-ray method used to measure bone density, is even better, experts say. But those tests can be expensive and are less convenient, often being done at a medical center or university laboratory.

        Near-infrared light wands give very localized assessments, just measuring the fat underneath the skin and not taking into account fat on the hips, thighs and stomach, said Wanda Howell, an associate professor at University of Arizona's Department of Nutritional Science.

        “It's easier, less invasive,” Ms. Howell says. “But we all vary so widely in regional distribution of fat” that measuring fat at the biceps isn't enough.

        Pamela Swan, an associate professor at Arizona State University's Department of Exercise and Wellness, says calipers measuring folds of fat and “electrical impedance” machines that use a mild electrical current to calculate body fat are accurate in the lab but not in the field. She did a study showing inaccurate caliper readings, compared with an X-ray method that also measures bone mass.

        “The biggest issue is making sure you have a reputable person doing the measuring,” Ms. Swan says. “I highly recommend that people don't put trust in the numbers.”

        For a reliable reading, a person must be well-hydrated but not have drunk or eaten much in the last four hours, not have exercised that day and not be sweaty, and women must be in the middle of their menstrual cycle. Most gyms don't follow these rules, she says.

        Even then there's a margin of error of 3 to 5 percentage points, depending on the measuring device and on the measurer's skill, Ms. Swan says.

        Chris Chapleau, a trainer and sales manager at World Gym in Tempe, Ariz., acknowledges that there's a margin of error, but he says body-fat tests are still a better measure of fitness than scale weights. That's because people in a fitness program might not lose much weight because they are gaining muscle, but they will lose body fat. Also, the percentage gives people proof they need to slim down.

        “People are 10, 15, 20 percent higher than they should be,” Mr. Chapleau says. “It's meant to be a scary number.”

        To minimize error, he says, people should be measured by the same certified trainer with the same instrument every four to six weeks, looking for a drop of about 2 percentage points.

        LA Fitness trainer and bodybuilder Tricia Travis thinks the machines give high readings. “They're used as a tool to sell a trainer, to sell machines,” she says.

        But Brett Bramsen, head trainer at the Scottsdale, Ariz., LA Fitness defends the system, saying he and other trainers have tested the near-infrared light machine's accuracy by comparing their own body-fat measurements using the machine and water displacement. The numbers were the same, Mr. Bramsen says. And even if the machine is off by 2 percentage points, it will be off the same amount each time you measure, so watch for the trend, he says.

        Instead of using body-fat percentage as the sole measure of fitness, go low-tech, say some fitness experts, suggesting:

        Belt test. A waistline of more than 40 inches for men and more than 35 inches for women puts a person at greater risk for heart disease, high-blood pressure, diabetes, stroke and other obesity-related diseases, according to the National Institutes of Health.

        Weight lifting. Compare amount you can lift on leg press, bench press and other exercises to what you lifted four weeks earlier.

        Clothes test. Do your clothes fit more loosely than they did than a month ago?

        Before-and-after photos. Some trainers use these to show improvement.

        Tape measure. Ms. Swan recommends measuring biceps, hips and thighs to register difference.

       



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