DEAR DR. DONOHUE: I am a 23-year-old woman who runs at least two marathons every year. My times are pretty good. I once ran one in three hours and 15 minutes. I run year-round, but in the winter I have to use an indoor track. After my last run, I felt like I was about to faint. It took three minutes for the feeling to go away. Does this mean anything? – T.N.

ANSWER: A faint is a sudden, short loss of consciousness from which a person recovers without any special intervention. A near-faint means a person didn’t lose consciousness but experienced the signals that usually appear before a faint – dizziness, sweating and nausea.

I am going to talk about fainting, but the remarks apply to near-fainting too.

Sometimes during but more often after exercise, a series of reflexes brings on a faint. Nerves to blood vessels become active and cause the vessels to dilate. That lowers blood pressure. In addition, the natural discomfort that comes from prolonged exercise can spark a different sort of nerve response, one that slows the heart. The combination of a blood-pressure drop together with a slow heartbeat decreases blood flow to the brain. The affected person faints. People who faint crumple to the ground. That puts them in the horizontal position, which is the best thing that could happen. In that position, gravity no longer draws and keeps blood in the lower half of the body. More gets back into circulation, and the brain receives its normal blood supply. The person wakes up. This kind of faint is not usually a sign of any trouble.

There are other, less common mechanisms that bring on a faint, and they can be serious — heartbeat abnormalities and heart problems such as cardiomyopathy.

I would like to give you assurance that all is well, and I believe it is, but I can’t do that without examining you. You’ll have to see a doctor to get that guarantee.

DEAR DR. DONOHUE: I have had to stop all exercise because my heels hurt. They don’t hurt on the bottoms, but they hurt on the inner sides, the ones that face each other. I can see little bumps under the skin. What is this? – L.B.

ANSWER: It could be piezogenic (pie-EE-zoh-GIN-ik) papules. “Peizo” is Greek for pressure, and papules are small bumps. Pressure causes some of the heel tissue to pop outward.

Heel cushions and elastic stocking might help you get over this. Doctors can inject the painful area with cortisone drugs, and that often eases the pain.

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.

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