PERSONAL HEALTH : How to Get Accurate Body Fat Readings
You might feel lean and mean. But how do you stack up on a body fat test--a measure that determines what percentage of your body is muscle and what percentage is fat?
For years, athletes have undergone such testing, often submerging in a water-filled tank to undergo “hydrostatic weighing,” considered the gold standard. But in recent years, as everyday exercisers have become more interested in body fat testing, more convenient methods have appeared.
Now it’s possible to get your fat measured at health clubs, health fairs, sports medicine clinics and maybe even your doctor’s office in a matter of minutes.
Some tests introduce a tiny electrical current; others beam infrared light at your biceps. Fees range from $10 to $45. But experts disagree about how accurate the new methods are, compared to hydrostatic weighing and other traditional tests.
And some exercise physiologists fear that consumers may become obsessed with their body fat level.
The Skinny on Fat
Why bother to find out your body fat percentage, especially if you suspect it’s nothing to brag about?
For starters, it may be helpful in assessing your overall level of fitness, since body fat level is one of four fitness components. (The others are muscular strength and endurance, flexibility and cardiorespiratory fitness.)
Too much body fat puts extra strain on joints and increases the risk of heart disease, high blood pressure and diabetes, according to the American College of Sports Medicine. But too little isn’t good, either; it may mean your body’s not functioning up to its potential.
Knowing your percentage of body fat--and reassessing it periodically--is useful in gauging progress on an exercise or weight-loss program, helping to ensure that you are gaining muscle and losing fat. As you age, keeping track of body fat may inspire you to exercise to maintain a healthy muscle-fat ratio. Even if scale weight doesn’t budge, body fat may increase if people remain sedentary over the years.
People who look slender may not have low body fat levels; people who tip the scale might be right when they say, “But it’s mostly muscle.”
The Ideal(s)
Experts disagree on ideal body fat percentage. Some give leeway with age. They concur that what’s ideal for men is too low for women. Men in their 20s, for instance, should aim for a body fat rating of 14%, according to guidelines from the American College of Sports Medicine, while women in their 20s should aim for 20%. (See the accompanying chart for other age ranges and ideals.)
The Old Ways
To undergo hydrostatic weighing, you immerse in a huge tank of water, submerging your head for 30 seconds or so. The amount of water displaced is directly proportional to your body’s volume. By calculating water displacement, the percentage of fat is determined.
Another traditional test involves an instrument called a caliper that pinches and measures the thickness of your skin folds at various sites; the measurements are used to calculate body fat percentage.
The Jolt Method
A very slight and harmless electrical current is introduced into the body via electrodes placed near the hands and ankles, says Michael Singer, a spokesman for RJL Systems, near Detroit, which manufactures one such unit.
This method, called bioelectrical impedance, works on the principle that the more fluid in the body, the less resistance to the electrical signal. “Generally speaking, leaner people have more water,” Singer says. Fatter people have less water and therefore produce more resistance to the signal.
Once resistance is measured, a printout detailing the muscle-to-fat ratio can be produced.
The Infrared Approach
Another technique beams infrared light at the biceps to measure body fat. “The leaner the person, the more light will reflect,” says Tori Tunnell, a manufacturer’s spokeswoman for Futrex 5000, one such infrared test device. “It’s as harmless as standing 10 feet away from a 60-watt lightbulb,” Tunnell adds.
A digital readout then gives percentage of body fat, basing the number on an equation built into the unit.
The Research
Manufacturers contend that the new devices correlate with traditional methods. For several years, exercise physiologists have compared the new methods to the old. Study results are mixed. Most agree that hydrostatic weighing is still the most accurate, but they acknowledge that it’s not convenient or accessible for many people.
Skin-fold testing, if done by a qualified person, is good enough, contends Gay Israel, professor and director of the Human Performance Laboratory at Eastern Carolina University, Greenville, N.C.
Perspective
“The ordinary person takes it (body fat) way too seriously,” says Glen Johnson, an exercise physiologist and professor in the department of health and human performance at the University of Nebraska, Lincoln. If you want to see where you’re at, by all means get tested, he advises. But don’t obsess. And recognize there’s often a wide margin of error.
How Much Fat Makes You Fit?
What is the recommended body fat level percentage?
Age (years) Men Women 20-29 14 20 30-39 15 21 40-49 17 22 50-59 18 23 60+ 19 24
Source: American College of Sports Medicine Resource Manual for Guidelines for Exercising Testing and Prescription, second edition.
