Painful, involuntary, sustained contraction of muscle in limbs or some internal organs. Causes may be neurological, reflex, or psychological. Common muscle cramps include swimmer's cramp from overexertion in cold water, heat cramps from loss of salt in sweat, leg cramps, and occupational (e.g., writer's) cramp. Menstrual cramps are uterine muscle contractions before or during menstruation. Cramps occur in diseases including parkinsonism and Huntington chorea. Tetany is severe cramping noticed first in limb muscles.