DEAR DR. DONOHUE: I could play tennis from sunrise to sunset if it weren’t for cramps in my calves. I don’t get them every day, but I get them enough that they’re a major nuisance. I’m in good shape and have been athletic my whole life. I am 43. What causes them? Is it the heat? How do I prevent them? – R.B.

ANSWER: A cramp is a painful, prolonged, involuntary muscle contraction. The cause is a matter of debate. Some say it’s dehydration. Others claim it’s a deficiency of sodium, potassium, magnesium or calcium. They might come on with muscle fatigue. Being in good shape ought to prevent muscle cramps, but it doesn’t. In Ironman contests during which contestants swim for 2.5 miles, ride a bike for 112 miles and run 26 miles, more than 6 percent of the participants have to seek medical help for muscle cramps. And these people are in top-notch shape.

Prevention depends on what you believe is the cause. Dehydration in hot weather could be the explanation. At least two hours before playing, and preferably three hours before, fill up with water. A sports drink with all the minerals they contain might be an even better choice.

During play, keep on drinking. If you’re a heavy sweater and lose a lot of salt, add a teaspoon of salt to a quart of water. You can tell if you’re a salt loser if you see a layer of white on your clothes after they dry. That layer is salt.

Stretch before playing. If you feel your calves beginning to twitch, stop and massage them. Massage is also good for an actual cramp. I’m told that pinching the skin between the upper lip and the nose quickly puts an end to muscle cramps.

DEAR DR. DONOHUE: I would like to know about the side aches I get when I walk or run. Why do they occur? Do I walk them off or take a break until they go away? – E.H.

ANSWER: What you call side aches, others call side stitches. Some feel they are spasms of the diaphragm – the large, thin muscle that serves as a partition between the chest and abdominal cavities and the muscle that is the principal breathing muscle. Or they might be due to too much food or fluid in the digestive tract. Some believe a decreased blood flow to the diaphragm is the cause. In truth, no one knows.

One way to get rid of them is to raise both your arms overhead while taking a deep breath. Then lower your arms while exhaling and simultaneously contracting your abdominal muscles.

Another favored treatment is to bend the knee on the side of the pain while pressing your fingers into the painful area.

Everyone gets them.

DEAR DR. DONOHUE: I work out with weights three times a week. The rest of the week I am active in my daily job. It requires lots of walking. Does it matter that I don’t get into my target zone for my heart to truly benefit? Do I need to work out my heart by serious cardio exercise during the week too? – C.A.

ANSWER: Any degree of exercise is better than no exercise, and any exercise benefits the heart.

You didn’t state your age. If you’re elderly, walking is an acceptable exercise for the heart. If you’re younger and if your doctor permits greater exertion, the faster you walk, the more of a burden you place on your heart and the better is the exercise. The “target zone” is the heart rate that provides the heart with optimum exercise. One way of obtaining it is to subtract your age from 220 and then use 65 percent of that number as the lower limit of your target zone and 75 percent of that number as the upper limit of your target zone. Take this formula with a grain of salt. It’s not as precise as you might be led to believe.

You can get a good estimate of how much exercise you’re giving your heart by perceived exertion. Does it feel like you are truly challenging your heart and your body with your exercise? That’s as good a way to determine cardiac benefits as any.

DEAR DR. DONOHUE: I had a CT scan of my abdomen, and everything on the report was OK except for this statement: “There’s a suspected splenic artery aneurysm, which is partly calcified and measures about 14 mm.”

I had another CT scan six months later and the report stated: “Examination again reveals the previously identified aneurysm which has a maximal diameter of about 16 mm.”

Neither of my doctors seems to be familiar with this condition. Any information will be greatly appreciated. I am 75 and on Coumadin. – V.P.

ANSWER: An aneurysm, no matter where it’s at, is a bulge in an artery wall – a weak spot. In the days when tires had inner tubes, a bulge of the inner tube through the tire approximates what an aneurysm is.

Aneurysms become a source of concern when they reach a certain size. In the case of a splenic artery aneurysm, the critical size is 20 mm.

Splenic artery aneurysms larger than that call for intervention. Sometimes that means surgery. At other times, the aneurysm can be obliterated by snaking a thin, pliable tube to the bulge through a surface blood vessel and releasing material that cause a clot. The clot closes off the aneurysm. It might be a trifle more difficult to achieve this procedure on someone taking the blood thinner Coumadin.

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