FAT OR FIT? NEW BODY MASS INDEX HELPS DETERMINE HEALTH, FITNESS

Above, personal trainers Larry Hagner and Jessica Berthold demonstrated the strength test for legs. Weights are added to determine how much weight someone can press in one repetition as part of the fitness assessment program.

Universal Health & Fitness Center personal trainers Larry Hagner and Jessica Berthold demonstrated the sit and reach flexibility test that determines a person's hamstring and lower torso flexibility.

Stepped on a scale lately?

Odds are, you or a friend -- or maybe all your friends -- are on a diet or thinking about starting one.

But the difference between fit and fat is more than poundage, fitness experts say, and your skinny friends aren't necessarily in good shape.

The real key to determining your fitness -- or fatness -- in body composition, says Bill Logan, director of wellness programs at St. Francis Medical Center.

Being in good shape means striking the right balance between lean muscle mass and body fat.

The scale can tell you how much you weigh, but it can't tell you what's fat and what's muscle, Logan said.

"You can step on a scale and that scale doesn't know if you're a sack of potatoes or a human being," he said.

And height-weight charts -- including the much-touted new Body Mass Index (BMI) -- aren't always reliable either, said Logan and Michelle Doughten, a fitness coordinator at Universal Health and Fitness Center.

The BMI indicator can't figure body composition, they said.

"You cannot use a height-weight chart because it doesn't take into account a person's muscle mass," Doughten said. "Body builders have a very high height-weight ratio, and if you would look at them on the height-weight chart, it would look like they're obese, and they're not."

Doughten said the BMI is "a rule of thumb, but they really don't tell you a whole lot."

Doughten and Logan use skinfold calipers to help determine body fat content.

For women, a healthy body fat content is 18 to 22 percent. For men, the range is 12 to 15 percent.

"Everyone that comes in here wanting to lose weight is so fixated on, I want to lose 30 pounds, or, I want to weigh 120, and it's not about that," Doughten said. "It's about high body fat, because a really skinny person can actually have a high body fat content."

The location of the body fat is also important, Logan said. People who are "apple-shaped" -- that is, they carry their extra weight around their stomachs and upper body -- are more at risk for heart attacks, he said.

As a general rule, though, Body Mass Index can be a good predictor of who is at risk for health problems because of excess weight, Logan said.

Excess weight is associated with high blood pressure and greater risk of heart attack, stroke, diabetes and some cancers.

The algebraic formula for figuring Body Mass Index is BMI=Kg/(m)2.

For those of us who slept through algebra, here are four easy steps for figuring your BMI.

-- Divide your weight in pounds by 2.2 to figure your weight in kilograms.

-- Divide your height in inches by 39.37 to determine your height in meters.

-- Figure the square of your height in meters.

-- Divide your weight in kilograms by the square of your height in meters.

The ideal BMI is between 19 and 22. A BMI higher than 25 is considered obese, and an indicator that weight loss is necessary.