A cramp is a sudden, involuntary muscle contraction or overshortening; while generally temporary and non-damaging, they can cause significant pain and a paralysis-like immobility of the affected muscle. Muscle cramps are common and are often associated with pregnancy, physical exercise or overexertion, age (common in older adults), or may be a sign of a motor neuron disorders. Cramps may occur in a skeletal muscle or smooth muscle. Skeletal muscle cramps may be caused by muscle fatigue or a lack of electrolytes such as sodium (a condition called hyponatremia), potassium (called hypokalemia), or magnesium (called hypomagnesemia). Some skeletal muscle cramps do not have a known cause. Cramps of smooth muscle may be due to menstruation or gastroenteritis. Motor neuron disorders (e.g., amyotrophic lateral sclerosis), metabolic disorders (e.g., liver failure), some medications (e.g., diuretics and inhaled beta‐agonists), and haemodialysis may also cause muscle cramps.