For the heraldic device, see cramp (heraldry); for the band, see The Cramps

Cramps are unpleasant, often painful sensations caused by contraction or over-shortening of muscles. Cramps can be caused by cold, overexertion or low calcium level in blood (especially for adolescents where they need calcium for both blood and bone maturing). Illness or poisoning can also cause cramps, particularly in the stomach, which is referred to as colic if it fits particular characteristics.

Causes

There are a number of causes of cramping: hyperflexion; hypoxia; exposure to large changes in temperature; dehydration; low blood salt; or low blood calcium. Muscle cramps may also be a symptom/complication of pregnancy, kidney disease, thyroid disease, hypokalemia or hypocalcemia (as conditions), restless legs syndrome, varicose veins, and multiple sclerosis.Muscle Cramps at WebMD

Electrolyte disturbance may cause cramping and tetany of muscles, particularly hypokalaemia (a low level of potassium) and hypocalcaemia (a low level of calcium). This disturbance arises as the body loses large amounts of interstitial fluid through sweat. This interstitial fluid is composed mostly of water and table salt (NaCl). The loss of osmotically active particles outside muscle cells leads to a disturbance of the osmotic balance and swelling of muscle cells as these contain more osmotically active particles. This causes the calcium pump between the muscle lumen and sarcoplasmic reticulum to short circuit and the calcium ions remain bound to the troponin and the muscle contraction is continued. This may occur when the lactic acid is high in the cells.

As early as 1965 it has been observed that leg cramps & restless legs syndrome can be a result of excess insulin, sometimes called hyperinsulinemia. Hypoglycemia & reactive hypoglycemia are also known to be associated with excess insulin insufficient glucagon and avoidance of low blood glucose concentration may help avoid cramps.

Iatrogenic causes

Statins are known to cause myalgia and cramps among other possible adverse reactions or side effects including substantially lowering blood glucose concentration1. Additional factors increasing probability for these adverse side effects are physical exercise, age, female gender, history of cramps and hypothyroidism. Up to 80% of athletes using statins suffer significant muscular adverse effects including cramps, the rate appears to be approximately 10-25% in typical population using statins. In some cases these adverse effects will disappear after switching to a different statin, however they should not be ignored if they persist as they can, in rare cases, develop into a more serious problem. Coenzyme Q10 supplementation can be helpful to avoid some statin related adverse effects but currently there is not enough evidence to prove effectiveness in avoiding myopathy or myalgia.