To burn fat, you have to work harder


December 01, 1992|By Dr. Gabe Mirkin | Dr. Gabe Mirkin,Contributing Writer

When you run, you burn 100 calories per mile, whether you run fast or slow. You keep essentially the same physical form when you run fast or slow, using the same motions and burning the same number of calories per mile.

Scientists recently studied two groups of men. One group ran 2 miles slowly -- in 35 minutes -- and burned 200 calories during their workout. The second group ran 2 miles fast -- in 17 minutes -- and burned the same 200 calories, but the faster group lost far more body fat. Why does intense exercise make you more lean?

A recent study conducted at the University of Virginia in Charlottesville tells us why. The more intensely you work out, the more growth hormone your body produces. Growth hormone causes your body to shed fat and build muscle.

What does this mean to the average person who exercises just to control weight? It means you should exercise more intensely once or twice a week. Every time you pick up the pace, however, your muscle fibers are injured. To avoid serious injury, you must allow at least 48 hours for recovery before you exercise intensely again. You should not work out intensely with the same muscle group more often than twice a week.

Those in an aerobic dance class can spend two days a week going more intensely. On the other days, exercise at a more leisurely pace or take the day off.

You can even get rid of extra body fat by lifting weights once or twice a week -- this will cause your body to increase its production of growth hormone markedly.


Q: Should a woman wear a bra when she exercises?

A: She can if she wants, but it isn't necessary. There is no evidence that exercising without a bra will damage or stretch the breast.

Breasts are held in place by the natural elasticity of the skin, and nothing else. There are fibrous bands, called Cooper's ligaments, that extend from the skin through the fat of the breast to the muscles underneath. But these ligaments have nothing to do with holding up the breast. Their function is to separate the breast into compartments.

On the other hand, breasts can bounce during exercise. The larger the breast, the more it bounces. This motion stretches the skin and can cause pain. All you have to do to stop the discomfort is to stop the motion.

Slight padding in a sports bra can help protect the breast from trauma. Snug-fitting bras can help decrease breast motion during exercise.

Q: Are electric blankets safe?

A: Several scientific articles have raised a question about whether sleeping under an electric blanket might increase your chances of developing cancer. But there is not enough evidence yet for you to throw away your electric blanket.

Twelve studies show that electrical workers who are routinely exposed to very high magnetic fields are at increased risk for developing leukemia. The incidence of leukemia is so low, however, and the increase in frequency so small that you cannot conclude electric blankets also cause cancer just because they also produce weak magnetic fields. Most electrical workers also are exposed to toxic chemicals that are far more likely to cause cancer.

Research shows children born to mothers who used electric blankets during their pregnancies were at slightly increased risk of developing leukemia and brain tumors. The studies found only a modest increase for a rare disease, so the incidence is extremely low. It may be the heat generated by the electric blankets caused the cancers -- several studies show extra heat during pregnancy can damage unborn children.

Since the studies that do show a weak association between electric blankets and health problems were done on children and pregnant women, those people probably should not use electric blankets. But others can choose for themselves. If you're concerned, you might substitute a good goose-down comforter.

Dr. Mirkin is a practicing physician in Silver Spring specializing in sports medicine and nutrition.

United Feature Syndicate

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