Jeff Boyd, age 14, of Winston Salem, N.C., for his question:

WHAT CAUSES A CRAMP?

A cramp is a condition in which either a group of muscles or a single muscle contracts and causes discomfort or pain. Sometimes there is only a single spasm, or contraction of the muscle. Other times there may be a continued series of spasms lasting for a long period of time.

Cramps often come about when certain muscles are used too much. If you were to write for a long time, you may develop writer's cramp. A cramp can also result from hard, muscular work in a hot place. And athletes often develop cramps in the muscles they use most strenously.

Among the best known cramps are those of the stomach and intestines. These cramps may be the result of poor eating habits or from chilling the stomach. They often cause common stomach aches. Stomach and intestinal cramps are also characteristic of many diseases, so if there is any question at all about the origin of the pain, a doctor should be seen quickly.