Muscle Spasms, Cramps, and Charley Horses

2. Why Muscle Spasms Happen

A muscle can become tired and cramp up when overused. A nocturnal leg cramp that tightens up at night while lying still, for instance, could be due to a long period of inactivity or, ironically, overuse of a muscle. A lack of electrolytes, water, or other minerals can irritate muscles, which can also lead to spasms. When a muscle fails to receive adequate blood supply, contractions can occur when the muscles are suddenly asked to become active.