Causes of cramping include
[1] 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
hypocalcemia (as conditions),
restless-leg syndrome,
varicose veins,
[2] and
multiple sclerosis.
[3]
Electrolyte disturbance may cause cramping and muscle
tetany, particularly
hypokalaemia and
hypocalcaemia. This disturbance arises as the body loses large amounts of
interstitial fluid through
sweat. This interstitial fluid comprises mostly water and salt (
sodium chloride). The loss of osmotically active particles outside of
muscle cells leads to a disturbance of the
osmotic balance and therefore shrinking of muscle cells, as these contain more osmotically active particles. This causes the calcium pump between the muscle
sarcoplasm and
sarcoplasmic reticulum to short circuit; the calcium ions remain bound to the
troponin, continuing
muscle contraction.
As early as 1965, researchers observed that leg cramps and restless-leg syndrome result from excess
insulin, sometimes called
hyperinsulinemia.
[4] Hypoglycemia and
reactive hypoglycemia are associated with excess insulin (or insufficient
glucagon), and avoidance of low
blood glucose concentration may help to avoid cramps.