Working harder at exercise outweighs working longer at it


If you've resolved to get in shape and lose weight, you should know that weight loss programs work best if they are based on two simple rules:

(1) Eat less and exercise more and (2) how hard you exercise is probably more important than how long you exercise.

A team of Canadian researchers has discovered that people who exercise vigorously have narrower waists and less fat beneath their skin than those who exercise at a more leisurely pace. This research confirms several previous studies showing that both rats and men who run fast lose more fat than those who run the same distance at a slower pace.

These results startle some exercise enthusiasts, because research has also shown that when you run, your body burns the same number of calories per mile, regardless of speed.

The explanation for why intense exercise helps you lose more weight has to do with what happens after you have finished exercising.

When you work out, your muscles use fuel -- sugar and fats -- for energy. More than 30 percent of that fuel is lost as heat, and you burn more calories as your body temperature rises. Also, your temperature remains high for several hours after exercising. The more intensely you work out, the higher your body temperature will rise and the longer it will remain elevated. Therefore, as time goes by, you will burn more calories long after finishing a hard workout than you will after completing a more relaxed session.

Q: I've been attending aerobic dance classes for nearly a year. Is it safe for me to keep going now that I'm pregnant?

A: A recent study by Dr. James Clapp of the University of Vermont showed vigorous exercise in the first three months of pregnancy did not increase the rate of birth defects or cause problems during pregnancy. This is welcome news since physicians have long been convinced vigorous exercise during pregnancy can increase body temperature and cause an oxygen debt, which may harm the unborn child.

Previous studies on animals and humans showed that women who exercised strenuously during their pregnancies, gave birth to smaller, but apparently healthy, babies.

High fevers in the first two months of pregnancy can lead to birth defects, particularly those involving the brain and spinal cord. After the fourth month, a high fever can lead to premature labor. Although exercise certainly can raise your body temperature dangerously high, there is no evidence that the elevated temperature caused by exercise will cause a birth defect.

If you exercised regularly before your pregnancy, you probably can continue to so do without any trouble. Be sure to talk with your doctor about it first. Exercise at a reduced pace and avoid high temperatures by exercising at a cooler time of the day, wearing lighter-weight clothing and drinking more fluids.

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

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