DEAR DR. DONOHUE: I am 27 and have been physically active all my life. I am pregnant and wonder if I can continue to be active during my pregnancy. My mother insists I should do nothing. She says exercise harms the fetus. Is that so? – R.K.

ANSWER: The only one who can give a woman the definite answer for the safety of exercise during pregnancy is her doctor. However, the answer for most women is: Yes, exercise is not only safe during pregnancy – it is encouraged. That’s especially true for women who have been physically active since long before their pregnancy.

Exercise during pregnancy keeps a woman from gaining too much weight. It helps keep blood sugar controlled. Blood sugar often rises during pregnancy. Exercise also maintains blood pressure in normal ranges. It prevents muscles from getting flabby.

Most pregnant women are able to perform 30 to 45 minutes of moderate-intensity exercise daily. Good pregnancy exercises include brisk walking, low-impact aerobics, swimming and stationary biking.

From the fourth month of pregnancy on, women should not exercise while lying on their backs. In that position the enlarging uterus can obstruct the flow of blood back to the heart. That causes a drop-off in the volume of blood pumped with each heartbeat.

Pregnant women should not exercise to the point of exhaustion. They should avoid becoming overheated and dehydrated.

Doing nothing is not a good way to prepare for delivery.

DEAR DR. DONOHUE: What is the appropriate rest time between sets of exercise? – R.G.

ANSWER: When a person has exercised a muscle to the point where it cannot perform another lift, it takes close to five minutes for the muscle to fully recover. However, a person doesn’t have to wait five minutes before beginning another set of lifts.

In only half a minute, nearly half the muscle’s energy has returned. In two minutes, about 95 percent has returned. If a person is engaged in lifting heavy weights, a rest of two to three minutes between sets of lifts is sufficient.

If a person is lifting light weights, less rest time is needed.

DEAR DR. DONOHUE: I am a 16-year-old girl, and I am attempting to gain weight. However, I seem to be cursed with a small rear and thighs. Is there any way that I can put weight on those areas without putting it in the middle region? – A.G.

ANSWER: There’s no way a person can direct calories for storage to a specific body area, nor is there any way that a person can siphon off stored calories from a specific body area. People believe that if they perform sit-ups, they’ll lose stomach fat – not so.

You can, however, build muscle in a specific area, and that will increase the size of that area.

For the buttocks, stand with a lightly weighted barbell behind your neck and resting on your shoulders. Your feet should be slightly apart. Step forward with the left foot and then genuflect with the right leg until the right knee touches the ground. Rise and repeat the exercise by stepping forward with the right foot and genuflecting with the left leg. When you’re getting the hang of this, do only a few repetitions with each leg. Gradually increase the number and gradually increase the amount of weight on the barbell.

For the thighs, squats are a good exercise. Stand in the same position as above, with a lightly weighted barbell resting in the same manner on your shoulders. Keep the back straight and bend the knees until the thighs are parallel to the ground. You need not bend any further. Don’t have the buttocks touch the heels. Such a deep bend puts too much stress on the knees.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from www.rbmamall.com.