The skinny on fat: ditch the scale to get a more accurate measure of your physical fitness

Muscle & Fitness/Hers, Oct, 2004 by Liz Neporent

Q: I've just started working out with weights but my weight hasn't really changed. Am I doing something wrong?

A: The number on the scale really doesn't tell you the whole story. Scales tell you little about your overall physical condition, and common weight charts don't differentiate between a lean, athletic 150-pound woman and a soft, sedentary one. In contrast, bodyfat percentage--a measure of the amount of fat you carry on your body vs. the amount of lean muscle tissue you have--is a better overall indicator of your health, physical condition and ideal weight. Experts recommend that women who want to maintain good health and reduce their risk of disease should maintain a 14%-30% bodyfat percentage. Besides health issues, you'll simply look and feel better if you stay at the lower end of that range.

There are many ways to test bodyfat percentage, all varying in convenience and accuracy. Here's the skinny on three common testing methods.

UNDERWATER WEIGHING, DONE AT A HOSPITAL OR UNIVERSITY: Considered the gold standard of bodyfat testing, this test involves getting dunked in a large tank of water, exhaling as much air as possible out of your lungs, then sitting on an underwater scale. Since fat is less dense than muscle, the more bodyfat you have, the lighter you'll be in water. A scientist uses this information to make calculations about body composition and density. The margin of error is 2%-3%.

SKINFOLD CALIPERS, DONE BY A CERTIFIED SPECIALIST: Commonly done in gyms, the tester pinches you with a spring-loaded tool called a caliper in 3-7 spots all over your body, then plugs the measurements into an equation to get an assessment of your fat-to-muscle ratio. Though human error and differences in skin quality can skew the results, this is usually a reasonably accurate measurement of bodyfat percentage.

BIOELECTRICAL IMPEDANCE SCALES, DONE AT HOME: These scales work by measuring a signal that travels through your lower body, from one foot to the other. A faster signal means you're more muscular. This is because water conducts electricity, and muscle is about 70% water; fat contains little water, so it "impedes" the signal. Although you can get a rough estimate of your bodyfat with home bioelectrical impedance devices, they're prone to error under certain conditions.

BY LIZ NEPORENT, MA, CSCS

Liz Neporent, co-author of Becoming a Personal Trainer for Dummies, is a certified personal trainer.