Nobody seems to know who Charley was or what his horse had to do with it, but it hurts like hell.

The sports pages of newspapers are riddled with stories of athletes who are suddenly laid low by a severe, cramping pain in their thigh muscle, a pain otherwise known as a charley horse.

The condition starts out as an exaggerated twitch in the thigh muscle and can rapidly develop into a full-blown muscle spasm lasting anywhere from 30 seconds to one minute. A very severe charley horse, however, can last much longer.

The medical term for the condition -- fibromyositis --

refers to pain, tenderness and stiffness of the joints or muscles. The tissues of the back, neck, shoulders, chest and thighs are usually involved. A charley horse specifically affects the thigh muscles.

Any sudden blow to a muscle or any intense exercise without a proper warm-up can cause the condition.

Muscles can contract to the point of "tightness," said Alexander Kalenak, an orthopedic surgeon and sports medicine specialist at the Milton S. Hershey Medical Center of Pennsylvania State University.

"If you contract the muscle tight enough, explains Kalenak, it can also impede the flow of blood to that muscle."

Dehydration and salt imbalances in the body also affect the sensitivity of muscles.

Athletes and avid exercise fans should drink water even when they don't feel thirsty, Kalenak said. The best preventive measures, however, may not save someone from a charley horse. Treatment usually includes an immediate massage or applying heat directly to the affected area. The trick is to get the muscle to relax.

Additional support for the muscle -- such as wrapping the thigh with a bandage or wearing a special girdle to support the muscle -- may also be necessary.

The real key to avoiding a charley horse, some sports medicine experts said, is to keep muscles supple by stretching before and after exercise.

"We see the problem early in the season when athletes are trying to get back into shape," said Kalenak. "Stretching is really crucial."