DEAR DR. DONOHUE: Lately, exercise has become a headache – literally. I belong to a gym, and I run on a treadmill, pedal a bike and lift weights. Two or three times a week, toward the end of the session, I develop a headache. What’s causing this? Would it be safe for me to take Tylenol before I exercise? – B.J.

Exercise-induced headaches are exertional headaches. There are many theories explaining why they occur.

Some say that the rise in blood pressure and the increased blood flow that come with exercise put traction on scalp arteries. Those arteries are sensitive to such changes. When they become engorged with blood whose pressure is higher than normal, they transmit pain signals that are felt as a headache.

If you suffer from migraine headaches, exercise often induces such headaches. I take it you would have told me if that was the case. For migraine headaches, medicine can be taken before exercise to prevent them.

Perhaps the biggest cause of exertional headaches is the Valsalva maneuver, which many people inadvertently and unknowingly practice during exercise. It commonly happens when lifting weights. People struggling to lift a weight close their mouths, throats and airways while they strain to maneuver the weight into position. That, in turn, raises pressure in veins and impedes blood return to the heart. Blood also congests the brain vessels and causes a headache. While straining, keep your mouth and throat open at least slightly. Make a conscious effort to exhale continuously and slowly while lifting the weight and to inhale when returning it to the starting position. Don’t hold your breath even for a second during the lift.

If you are not performing a Valsalva maneuver and if your headaches are short-lived, it is permissible to take Tylenol before exercising. However, it is not permissible to do this indefinitely, and it is not permissible to do it if your headaches last a long time. In such cases, which are admittedly rare, serious problems could be at work. Two examples are a brain tumor and a blood leak from a brain artery.

If your headaches persist, you must see a doctor.

DEAR DR. DONOHUE: I am a high-school tennis player. I am good but not great. My coach says I don’t react quickly enough after the ball has been hit back to me. He fails to say how I can learn to react more quickly. Do you have any suggestions? – K.R.

Professional tennis players wait only 400 milliseconds after their opponent has hit the ball before they begin to move to the spot where the ball is going to return. A millisecond is one-thousandth of a second. Not a very long time. Even 400 milliseconds is not much more than a blink of the eye.

Paint letters or numbers on practice tennis balls. As soon as your practice opponent’s racket strikes the ball, look for the painted number on it. This is a good way to track the ball and to react quickly in getting yourself into position for your next stroke.

When you master the above exercise, turn your back to your practice opponent and have him or her yell when he or she hits the ball. Then turn around and again concentrate on seeing the number on the ball.

I know this sounds far-out, but it works. At least I am told it works.

Incidentally, this exercise can be used as training for any sport where a ball or other object is propelled between two players.

DEAR DR. DONOHUE: I am 83 and walk about 1.5 miles each day when the weather permits. I cannot walk the pace you suggested. Is my walking doing any good? I also have a stationary bike. Does it help when weather keeps me indoors? – R.

You do not have to follow any set of rules to maintain your health. You are living proof that your exercise is more than adequate. We should follow your regimen. Keep walking just as you have been. There is no reason for you to change, and it is doing you a world of good.

Sure, the bike is an acceptable substitute for walking.

DEAR DR. DONOHUE: My niece suffers from arthritis very badly. She discovered that her arthritis might be something called HLA-B27. Her doctor confirmed it. Would you please write something about it? – J.G.

All body cells are imprinted with personal identification numbers. That’s not what they are called, but they remind me of a PIN. Those PINs tell the body which cells are its cells and which are invading aliens, germs being an example. If the cell’s or germ’s PIN is not registered in the body’s data bank, the immune system attacks it.

HLA-B27 – human leukocyte antigen B27 – is a PIN found on white blood cells (leukocytes). Some forms of arthritis are associated with this PIN. A special kind of back arthritis – ankylosing spondylitis – and the arthritis that some psoriasis patients have are found frequently in people who carry the HLA-B27 marker.

HLA-B27 is not a distinct kind of arthritis. It is a piece of evidence that can help doctors establish which variety of arthritis a patient has.

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.

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