A cramp is a sudden, brief, usually painful contraction of a muscle or group of muscles.
Muscle cramps (also called charley horses) can occur in healthy people (usually middle-aged and older people), sometimes during rest but especially during or after vigorous exercise. They occur in younger people less often. Some people have leg cramps during sleep. These painful cramps usually affect the calf and foot muscles, causing the foot and toes to curl downward.
Having tight calf muscles is a common cause of leg cramps. Muscles become tight when they are not stretched, when people are inactive, or sometimes when fluid repeatedly accumulates (called edema) in the lower leg. Low levels of electrolytes, such as potassium, in the blood can also cause cramps. Low potassium levels may result from use of some diuretics or from other conditions that cause loss of fluids (and thus electrolytes—see Electrolyte Balance: Hypokalemia).
People who have hardening of the arteries in the legs (peripheral arterial disease) may develop calf pain with exertion. This pain is due to inadequate blood flow to muscles, not to a muscle contraction as with a cramp.
Prevention and Treatment
Preventing cramps is the best approach. The following measures can help:
Stretching helps because it makes muscles and tendons more flexible and less likely to contract spontaneously. The runner's stretch is the best stretch for preventing calf cramps. A person stands with one leg forward and bent at the knee and the other leg behind with the knee straight—a lunge position. The hands can be placed on the wall for balance. Both heels remain on the floor. The knee of the front leg is bent further until a stretch is felt along the back of the other leg. The greater the distance between the two feet and the more the front knee is bent, the greater the stretch. The stretch is held for 30 seconds and repeated 5 times. Then the set of stretches is repeated on the other side.
Most of the drugs prescribed to prevent cramps from recurring (including quinine sulfate, magnesium carbonate, and benzodiazepines such as diazepam) have not proved to be effective and can have side effects. Mexiletine (used to treat abnormal heart rhythms) sometimes helps but has many side effects. Calcium supplements are safe and have few side effects, but they also have not proved to be effective.
If a cramp occurs, stretching the affected muscle often relieves the cramp. For example, for a calf cramp, the person could use a hand to pull the foot and toes upward or do the runner's stretch. Muscle pain from inadequate blood flow is relieved by rest rather than stretching.
Last full review/revision April 2008 by Joseph J. Biundo, MD