DEAR DR. DONOHUE: Our 11-year-old son plays competitive basketball. After a strenuous game or practice, he often gets headaches. We took him to his doctor last year, and the doctor checked his eyesight. It turns out he is nearsighted, so we got him glasses. The headaches have continued, and they usually last one to two hours after a game or practice. Do you have any suggestions for us? – W.D.

ANSWER: Your son could be having exertional headaches.

During physical activity, blood flow to the head, brain and scalp increases, and the pressure in arteries serving those areas also increases. That’s natural and normal, and most people suffer no consequences.

For some, however, the artery distention caused by the increased blood flow and rise in pressure becomes painful, and a headache blossoms. It’s a throbbing headache, which can be on both sides of the head, or it can be centered in the back of the head.

Watch your son when he practices. See if when he shoots the ball – especially a long shot – he holds his breath. If he’s doing that, he’s creating increased vascular pressure, and that can either bring on the headache or make it worse.

If he’s not doing that, then a trial of an anti-inflammatory medicine before practice or a game could abolish the headaches. Aleve, Advil and Indocin are examples of those medicines. Use the smallest dose possible, and experiment with it. If it stops the headache, let him take it two or three days in succession. Then stop the drug and see what happens. The headaches might not return.

Even though the doctor has examined him once, it would be a good idea for him to have a second checkup. There are other causes of headache that should be considered. A previous head injury, for instance, can cause headaches well after the injury occurred.

DEAR DR. DONOHUE: I will be 86 in January 2008. My days are spent at or traveling to and from the gym. I love both aerobic and weightlifting exercise. Recent heart tests show that I have an ejection fraction of 65.

I have noticed in the past year or so that when I am on the treadmill, I perspire very little. Fellow exercisers are wringing wet with sweat.

I feel that I would be more comfortable from the cooling effect of sweat. Also, my skin is very dry.

What, if anything, can be done to enhance my sweating? – H.M.

ANSWER: Older people produce less sweat because their sweat glands don’t work as well as they did in youth. Their skin dries because oil glands also slow their production of skin oil.

You can handle the dry-skin problem with the daily use of moisturizers.

Sweating is one of the ways the body keeps its temperature from rising too high. If you are very hot and dizzy after exercising, then your temperature might be rising. I can’t give you any way to increase your sweating, but you can keep your body temperature at more normal levels by drinking cool water during your exercise.

If, on the other hand, you feel shortchanged just because your fellow exercisers sweat more, don’t sweat the lack of sweat.

Do you realize what good shape you are in? An ejection fraction of 65 indicates that your heart is pumping as strongly as the heart of a teenager.

DEAR DR. DONOHUE: You recently discussed heart-rate information. I am 65 and have a resting heart rate of 72. I have done aerobic exercise for more than 30 years. I am now on a medication that doesn’t let my heart rate rise higher than 120 beats a second. The medicine is atenolol. My maximum heart rate should be 150. Is reaching only 120 benefiting me? – J.P.

ANSWER: Your maximum heart rate should be 150 (220 minus your age). However, your maximum training heart rate should be only 131, 85 percent of 150. You’re not far from that number.

Your medicine is a beta blocker. Those drugs slow the heart. You’ll never get your heart to a predicted level, and you shouldn’t try. You’re benefiting from your exercise all the same. Stop counting your heartbeats.

DEAR DR. DONOHUE: Do blood thinners dissolve blood clots?

I am taking the blood thinner Coumadin for a clot I have in a leg vein. How long does it take to dissolve the clot? – A.S.

ANSWER: Blood thinners like Coumadin don’t dissolve blood clots. They keep the clot from growing larger and prevent other clots from arising.

Vein clots shrivel in time, or a tunnel bores its way through the clot so blood can resume flowing. Rarely, however, a clot can become a permanent obstacle to blood flow through the affected vein.

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