DEAR DR. DONOHUE: I am 31, athletically active and love most sports. In 1996, I severely sprained my left ankle and was in a cast and on crutches for six weeks. I re-sprained the same ankle in 2003. Since then I have sprained the same ankle numerous times. Now I have pain in this ankle, sometimes minor and sometimes strong. What could fix my ankle? – J.J.

ANSWER: Recurrent ankle sprains indicate ankle instability due to permanent ligament damage. Ligaments are bands of tough fibers that span joints to keep them in place and to steady them. A sprain is a stretched or torn ligament.

Most ankle sprains involve the ligaments on the outside of the ankle. When the foot strikes the ground, ankle ligaments keep the joint aligned. However, with lax ligaments, the foot turns upon ground strike – the sole of the foot faces the opposite leg – and the ankle ligaments are stretched beyond the point of their elasticity. Ligaments are torn. Your ankle appears to have permanent ankle ligament damage that gives you ankle pain and instability.

An elastic ankle brace could help. Or you can tape your ankle before exercising. Sometimes a small, lateral heel wedge prevents the ankle from turning in when the foot hits the ground.

If you can get an elastic exercise band, found in most sporting-goods stores, you can do an ankle exercise that strengthens the joint. Sit on the floor with the legs outstretched in front of you. Loop the elastic band around the ball of the foot and hold the ends of the band in your hands. Pull the foot toward you while resisting the pull by pushing the foot away and downward.

I believe, however, you’re going to need the services of an orthopedic surgeon. Your ankle problem might be the kind that can be fixed only by reconstruction of the ankle ligaments.

DEAR DR. DONOHUE: I work in a large building that has long corridors. I don’t have any time to exercise when I get home, but I can walk the halls of my building every hour for five to 10 minutes. My boss encourages us to do this. How much walking do I have to do to get the sort of exercise that really benefits my body? – K.J.

ANSWER: You can get all the exercise you need by walking in your hourly 10-minute breaks.

How about buying a pedometer? They’re not terribly expensive. They’re in the $10 to $20 range. They’re worn at the waist and record the number of steps you take. Once there was a big push for everyone to walk 10,000 steps a day. That’s five miles, 2,000 steps being a mile. (Please don’t write. I know the distance can be determined only by knowing the length of a person’s stride, but this is only a rough estimate of distance.) If your total daily steps, including all the steps you take when you’re not formally exercising, total 10,000, you’re doing enough exercise.

If you want to know how fast to walk, the speed should be 100 to 150 steps in a minute. That’s pretty fast, and if you can’t walk at that rate, don’t worry about it.

DEAR DR. DONOHUE: I used to jog for exercise, but my knees began to bother me. I changed to speed walking, and my knees no longer bothered me. When it’s raining or snowing outside, I run up and down the stairs. I’m in my mid-60s.

Since my pulse rate is 135 beats a minute whether I walk or run the stairs, are they both equal?

Why don’t my knees bother me when I run up and down the stairs, like they did when I jogged? – F.H.

ANSWER: You can use your pulse as a guide to exercise intensity. If the two exercises raise your heartbeat to the same rate, they’re equivalent in their physical demand.

Climbing stairs on a run is very strenuous exercise. With each step, your body weight battles gravity more than it does when running on a level surface. Walking up stairs is the equivalent of running a mile in 11 minutes. You’re running up the stairs, which is even more strenuous. You’ve checked with your doctor about this, I hope.

The knee question is one I can’t answer. Most people with knee problems complain about stair climbing. Does anyone out there have an explanation for F.H.?

DEAR DR. DONOHUE: I have an unusual and slightly embarrassing question. At the peak of intense orgasm, I experience an excruciating headache. It is unbearable, but it subsides fairly quickly. It has happened three times now. Have you ever heard of this? – P.M.

ANSWER: That’s called an intercourse or coital headache. It’s a headache that occurs just as you describe. It is one of intense pain and abrupt onset that happens during or immediately after intercourse. It goes away in a few minutes.

If the headache lasts any longer, then it could be an indication of something much more serious, like a bleed in the brain.

You might be able to prevent such a headache by taking the anti-inflammatory medicine Indocin or the beta-blocker drug Inderal an hour or so before sexual relations. They’re both prescription medicines, so that gives you an opportunity to tell your doctor about the headaches.

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