A Charley Horse in Bed

Q. Why does one get muscle cramps while sleeping or resting?

A. In most cases, there is no apparent cause for hard knots in the muscles, usually in the calves, that are not associated with vigorous exercise, medical authorities say. Nighttime attacks of leg cramps are quite common, especially in older people, and can be very painful though usually not dangerous.

Most night cramps are not associated with serious underlying diseases, but diabetes and circulatory problems are among the conditions that should be ruled out by a doctor, especially if the cramps are frequent and severe. Cramping can also be a side effect of some prescription drugs.

One popular suggested explanation for the involuntary contractions involves overactive nerve networks in the large leg muscles, but there is no conclusive evidence as to whether this is true or what the cause may be.

Other researchers suggest that cramps are an effect of dehydration, which is known to be involved in spasms after exercise. Common sense suggests drinking enough water through the day and before going to bed, as well as avoiding heavy bed covers that keep the toes from pointing up. Gentle stretching exercises may help.

If you develop a cramp, you can help relax the knotted muscle with gentle stretching and massage; walking or standing if you can manage it; and perhaps a warm bath or shower.

C. CLAIBORNE RAY

Readers may submit questions by mail to Question, Science Times, The New York Times, 620 Eighth Avenue, New York, N.Y. 10018, or by e-mail to question@nytimes.com.