DEAR DR. DONOHUE: My son plays high-school basketball. I attended one of his games with a friend who happens to be a nurse. Twice during the game, my son became quite winded and started coughing. He had to be taken out for a rest. My friend thinks he might have asthma. How do I get him tested for it? If he has it, will he have to stop athletics? That would break his heart. – K.K.

ANSWER: Your friend suggests your son might have exercise-induced asthma, and most of the people who have it have asthma attacks only upon exercising. It’s not rare. It affects up to 20 percent of the general population.

Rapid breathing engendered by exercise cools and dries the airways. That’s a stimulus for some people’s airways to abruptly narrow and obstruct the flow of air into and out of the lungs.

Coughing and wheezing are symptoms. However, many react with more subtle symptoms, like chest tightness or unwarranted fatigue. Symptoms appear during exercise or sometime after exercise. They usually go away in 30 to 60 minutes.

If your family doctor believes your son’s symptoms might be due to exercise-induced asthma, the doctor can exercise him in the office to precipitate an attack and then measure his breathing function.

If your son does have the condition, his days of playing sports are not over. One simple way of combating airway narrowing is to breathe only through the nose. The nose warms and humidifies air before it reaches the airways. If need be, asthma medicines, inhaled from a spray, can prevent these attacks. Do have your son checked. Your friend might have made a good call.

The asthma booklet provides the details of this common lung malady. Readers can order a copy by writing: Dr. Donohue – No. 602, Box 536475, Orlando, FL 32853-6475. Enclose a check or money order for $4.50 U.S./$6.50 Can. with the recipient’s printed name and address. Please allow four weeks for delivery.

DEAR DR. DONOHUE: I have played competitive tennis for 65 years, but arthritis has ended it. I now ride a recumbent stationary bike and find that 30 or 40 minutes of pedaling works up a sweat. Is this enough exercise for cardiovascular fitness? – J.C.

ANSWER: In 1995, the guidelines for cardiovascular exercise stated that 30 minutes of moderate-intensity exercise on most, if not all, days of the week was required. “Moderate-intensity” exercise is the equivalent of walking briskly or raking leaves.

Two years ago, experts upped the amount of time to one hour of exercise a day. The exercise does not have to be done all at once. It can be broken down into two 30-minute sessions or four 15-minute ones. A full hour of exercise is not feasible for many people, so some experts interpret the hour to include all physical activity, not just the time devoted to exercise alone.

Another expert panel feels that accruing 700 calories of exercise in a week suffices for cardiac conditioning. Walking at a pace of 3 miles an hour for 30 minutes, seven days a week, burns 1,050 calories. It more than fulfills that requirement.

Your exercise puts you far over that amount. Your biking burns more calories than doubles tennis and slightly less than singles tennis. You are doing just fine.

DEAR DR. DONOHUE: My exercise is treadmill running. I do it seven days a week, and I spend close to 45 minutes a day doing it.

A friend tells me I am not getting a true workout because I hold on to the side rails of the treadmill. Have I been wasting my time? – A.P.

ANSWER: When a person holds on to side rails as if for dear life, he or she takes some weight off the legs and does diminish exercise intensity. Unless you are into very precise measurements of calorie burning, you don’t have to worry about this. You are getting valuable exercise.

Many people have to hold on to the side rails to keep their balance. It’s permitted.

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.