A cramp is a sudden, and involuntary muscle contraction or over-shortening; while generally temporary and non-damaging, they can cause mild-to-
excruciating pain, and a paralysis-like immobility of the affected muscle(s). Onset is usually sudden, and it resolves on its own over a period of several seconds, minutes, or hours. Cramps may occur in a skeletal muscle or smooth muscle. Skeletal muscle cramps may be caused by any combination of muscle fatigue, a lack of electrolytes (e.g., low sodium, low potassium, or low magnesium) Cramps of smooth muscle may be due to menstruation or gastroenteritis.
Causes of cramping include hyperflexion, hypoxia, exposure to large changes in temperature, dehydration, or low blood salt. Muscle cramps may also be a symptom or complication of pregnancy, kidney disease, thyroid disease, hypokalemia, hypomagnesemia or hypocalcaemia (as conditions), restless-leg syndrome, varicose veins, andmultiple sclerosis.