Researchers suggest slow excercises have low impact on fat and fitness HURRY UP AND WEIGHT

August 16, 1994|By Colleen Pierre, R.D. | Colleen Pierre, R.D.,Special to The Sun

In recent years, more people have turned to slower-paced workouts -- the so-called "fatburner" classes -- as a way to lose weight. But a growing number of health experts say it's simply a myth that light exercise will melt away the pounds faster than strenuous exercise.

The idea behind these classes sounds reasonable. In the early stages of exercise, before the body is fully revved up, the greatest percentage of calories burned comes from fat. As the workout picks up, the body burns more carbohydrates.

So it would seem logical that a full workout at a low-aerobic pace would burn more fat and take off more weight -- and everyone from "Fit or Fat" author Covert Bailey to the inter-national association that certifies aerobics instructors jumped on the bandwagon.

But this simply isn't so.

If your goal is to lose weight, doctors say, the key is not what kind of fuel the body uses during exercise -- fat or carbohydrates. It is how many calories you burn, and whether you eat enough to replace them.

The only way to take off pounds is to burn more calories than you take in.

"Finding where the fuel is coming from has spiraled into misinformation promoted by aerobics instructors and other professionals in the industry," says Dave Petrie, director of the Human Performance Laboratory of Union Memorial Hospital's Sports Medicine Center. Mr. Petrie has been noticing this trend for about a year. Patients who came to him for fitness evaluations often ranked low in aerobic conditioning despite investing a lot of time in regular exercise. Worse yet, they weren't losing weight.

In talking with patients, he discovered that they had slowed their workouts to a snail's pace to take advantage of fat burning. What they'd really done, he said, was limit their aerobic fitness, burn fewer calories and make it harder -- not easier -- to lose weight.

Reasonable stress from exercise -- that is, raising the heart rate to between 60 and 85 percent of maximal heart rate -- is healthy, Mr. Petrie says.

It strengthens the heart so it pumps harder and delivers more oxygen to muscles and more nutrients to the body. Not to mention that such aerobic conditioning makes people feel great, while it reduces their risks for heart attacks.

Local aerobics instructors, however, defend the "slower is better" approach, especially as a boon to beginners.

'Fatburner' classes

Twenty percent of the aerobics classes at Merritt Fitness Center in Towson are called "fatburner" classes. Kim Thomas, Merritt's director of aerobics, says she finds many people afraid to try aerobics because they can't last for an hour.

"I tell them it's OK to go at a slower pace, because you won't burn out so fast," she says.

Health experts say that is sound advice for beginners. But working out hard for 10 or 15 minutes, then dropping out, doesn't burn many calories of any kind and can be discouraging. Therefore, a bargain must be struck between going long and going fast.

Many newcomers need a breaking-in period. In a sense, they're in training for exercise, gradually tuning body parts to be able to tolerate a more normal level of activity.

Jack Wilmore, Ph.D., professor of kinesiology and health education at the University of Texas at Austin, agrees that a breaking-in period is needed for beginner exercisers. But he also agrees it shouldn't be an end in itself.

He was a member of the 1992 panel of the American College of Sports Medicine and the Centers for Disease Control, which reached a consensus that some people are so sedentary that a total of 30 minutes a day of any kind of activity, even gardening or strolling to the store, would improve their health.

"But that message was not intended for people who have already started," he says. "Even more [exercise] than that will provide considerably more benefits."

The fallacy of the notion that low-impact workouts help lose weight, he notes, is revealed in one fact.

"Sleep! That's when you burn the highest percentage of fat," Dr. Wilmore says.

Slow burning

He adds that slow-paced workouts don't burn many calories, and that even during the early fat-burning stages of exercise the number of grams of fat the body uses up is very low.

The numbers bear this out. Thirty minutes of walking at 3 mph will burn 260 calories, 50 percent (130 calories) from fat, and 50 percent (130 calories) from carbohydrates.

Pick up the pace to 4 mph for that same 30 minutes and the individual can burn 350 calories, 40 percent (140 calories) from fat, and 60 percent (210 calories) from carbohydrates.

"Exercise in and of itself has little effect on weight loss," Dr. Wilmore notes. "It's a part of a total program, but [losing weight] can't be done without altering diet. Either composition or total number of calories have to be altered."

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