Answer: Swimming is at the top or near the top of exercises. The people at the Cooper Clinic in Dallas, the place where aerobics started, have shown that regular swimmers and regular runners have the lowest cholesterol, the best blood pressure and the greatest body strength for supporting physical activity. Swimmers have the lowest death rate. Furthermore, it's an exercise that puts little stress on joints. The only place where it doesn't offer great results is in the prevention of osteoporosis.

Sixty-nine is not too old to learn how to swim. I can give you a few tips, but you need a swimming coach to learn proper techniques. The local Y is a place to find such an instructor. I'm sure there are other facilities near your home, too.

Swimming burns around 600 calories an hour. Calorie burning depends, of course, on the stroke used and the intensity of the swim. The butterfly stroke and the crawl (freestyle) burn up to 750 calories an hour.

Breathing should be natural. You don't have to take a breath with each stroke. When your face is in the water, exhale through the nose and mouth. When you feel you're running out of breath, don't hold off, but take some air.

If people are into counting their heart rate (pulse) to gauge their exercise intensity, in water the heart rate doesn't rise as high as it does during land exercise. It is 10 to 15 beats a minute slower.

Dear Dr. Donohue: My wife of 58 years is 82 and 5 feet 5 inches tall. She has had a stomach like she's seven months pregnant for the past six years. She used to weigh 133 pounds. A year ago, she lost weight and went to 127 pounds, but her stomach remained the same. She has had many tests, but nothing has been found. Her doctor told her to exercise more. Three weeks ago, she came down with shingles, and her weight dropped to 122 pounds. Her stomach is the same. What can she do? — B.M.

Answer: Like you and your wife, I have to rely on her doctors to assure that nothing bad is happening in her digestive tract.

Your wife doesn't need to lose any more weight. She needs to strengthen her abdominal muscles. With age, all muscles shrink and lose strength. When that happens to abdominal muscles, abdominal organs make the abdomen protrude. She can regain some abdominal-muscle strength by sitting in a chair, slightly forward from the back of the chair. The chair should be firm and sturdy. You hold on to it so it doesn't tip over. She raises her knees, drawing them upward and inward toward the abdomen and lower chest. When she gains proficiency, she should try for 10 consecutive raises. With more proficiency, she can do a second set of 10 exercises.

She also has to work with her back. Age weakens the backbones. The lower back tends to curve inward and push the abdomen out. She can correct this by standing with her back against a wall and trying to flatten the inward curve of the lower back. She has to maintain this posture, sitting, standing and walking. It will reduce her abdominal bulge.

Dear Dr. Donohue: What professional sport has the best-conditioned athletes? — L.C.

Answer: You're going to get me into hot water. One survey states that professional hockey players have the least amount of body fat, 10 percent to 12 percent. That indicates excellent conditioning.