Trying to get in shape? Then don't depend on your bathroom scales. To getthe most accurate measure of your progress, experts say, you need to track yourbody fat as well as your weight.

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"Most people focus only on losing weight, not on the fat," Cedric X.Bryant, PhD, chief exercise physiologist with the American Council on Exercise,tells WebMD.

"Preserving lean tissue and losing body fat -- that's what you need tostrive for," Bryant says. "The only way to know how you're doing isthrough some form of body-composition assessment."

You know about the old standard measuring tools, like the body mass index(BMI) and the tape measure. And thanks to today's technology wizards, some verygood new devices are available to measure your body fat.

To learn which are worth your time and money, WebMD got ratings from Bryantand from two more top exercise physiologists: Megan McCrory, PhD, an energymetabolism scientist with the Jean Mayer USDA Human Nutrition Research Centeron Aging at Tufts University in Boston; and Len Kravitz, PhD, senior exercisephysiologist for IDEA Health and Fitness Association.

The BMI Test

This is a simple calculation, using the most basic tools -- your height andweight. Plug these numbers into a BMI calculator to learn whether you areobese, overweight, or normal weight.

The BMI was developed using large, population-based studies. Though itdoesn't address percentage of body fat or muscle, it helps health careprofessionals quickly assess which patients may be at risk of health problemslinked to excess weight.

Price: None.

The verdict: Free and readily available; good for assessinghealth risks but doesn't measure body-fat percentage. If you are short, or verymuscular, results tend to be less accurate.

"It's a good starting point, a really good way to get a basic estimateof whether you are overweight or not," says Bryant. "BMI tends tocorrelate pretty closely with health risks associated with being overweight orobese."

The experts' grade: D. "The BMI doesn't give you bodyfat measurement," says McCrory. "But if gives an excellent BMImeasurement!"