Muscle Cramps

A cramp is a sudden, brief, usually painful contraction of a muscle or group of muscles.

Cramps are common among healthy people, especially during or after vigorous exercise. Middle-aged and older people commonly have cramps after light exercise or during rest. 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.

Cramps may be caused by inadequate blood flow to the muscles. For example, they may occur after eating, when blood flows primarily to the digestive tract rather than to the muscles. Low blood levels of electrolytes, such as potassium, can also cause cramps. Low potassium levels (see Section 12, Chapter 155) may result from use of some diuretics or from dehydration.

Cramps can usually be prevented by not exercising immediately after eating and by gently stretching the muscles before exercising or going to bed. Stretching makes the muscles and tendons more flexible and less likely to contract spontaneously. Not consuming caffeine (for example, in coffee or chocolate) and not smoking also help to prevent cramps. Drugs that are stimulants, such as ephedrine or pseudoephedrine (a decongestant contained in many over-the-counter products), should not be used if cramps are a problem. Drinking plenty of fluids (particularly beverages that contain potassium) after exercise also helps to prevent cramps.

Most of the drugs prescribed to relieve cramps (including quinine sulfate, magnesium carbonate, and benzodiazepines such as diazepam) have not proven to be effective and can cause side effects. Calcium supplements are well tolerated, but they also have not proven to be effective. Mexiletine sometimes helps but has many side effects.