These cramps can be extremely painful and can even rouse you from a deep sleep. Daytime cramps are also possible in muscles throughout the body, including the thighs, back, hands and arms. Doctors suspect that muscle cramps are often related to mineral deficiencies, says Dr. Iglarsh. Magnesium and calcium in particular are believed to play central roles in muscle contraction and relaxation, so a lack of them may bring about cramps. So might shortages of potassium and sodium, which also trigger the contraction and relaxation of muscles.
Exercise can reduce the body's mineral reserves because potassium and sodium are lost in sweat.
Dehydration is also thought to cause cramps. People who are out of shape run an increased risk of getting cramps because poorly conditioned muscles get fatigued more easily, says Paul Davidson, M.D., associate clinical professor of medicine at the University of California in Greenbrae and medical director of the Fibromyalgia Clinic at Kentfield Rehabilitation Hospital in Kentfield, California. That's because swelling deprives the calf muscles of the nutrients they need. Also during pregnancy, the fetus draws on the mother's mineral stores, which may lead to depletion, she says. Your sleeping position may also be the culprit.