A cramp is an involuntary and forcible contraction of a muscle that does not relax, according to the American Academy of Orthopaedic Surgeons. Cramps can occur in any skeletal muscle, but one of the most commonly affected muscles is the gastrocnemius in the calf of the leg. Calf cramps may be mild or severe, and can occur during the day or at night. Nocturnal leg cramps--those that occur at night--are most common in teenagers, pregnant women and people older than 50. Severe and frequent muscle cramps that are not related to exercise and do not respond to home treatment should be discussed with a health care provider.
Electrolyte Depletion
Exercising in hot weather causes loss of fluids and electrolytes--salt, potassium, magnesium and calcium--through the sweat, causing muscles to cramp. Some diuretics prescribed for high blood pressure cause the body to lose potassium, increasing the likelihood of cramps. Eating a diet that is poor in potassium, magnesium and calcium also can result in muscle cramping.
Muscle Fatigue
Over-exercising without stretching first to lengthen the muscle fibers can cause the muscles to become fatigued, depleting their oxygen supply, notes the American Academy of Orthopaedic Surgeons. Waste products build up and when the muscle begins to spasm, the spinal cord stimulates the muscle to continue contracting. Prolonged standing or sitting can cause muscle cramps at night, also known as nocturnal leg cramps.
Skeletal Disorders
Lumbar stenosis--a narrowing of the spinal vertebrae--compresses the nerves and can cause cramping pain in the legs that worsens as you walk. Flat feet and other structural problems can also contribute to cramping.
Medical Conditions
Medical conditions such as diabetes, anemia, thyroid disease, Parkinson’s disease and kidney disease can cause cramping in the calf. Patients on dialysis for kidney failure are also prone to leg cramps. Peripheral artery disease, a circulatory problem involving narrowed arteries and reduced blood flow to the limbs, causes mild to severe cramps--intermittent claudication--in the calf while walking that disappear after a few minutes of rest.
Pregnancy
Nearly 50 percent of pregnant women have muscle cramps in their legs, especially at night, reports the American Pregnancy Association. Weight gain, changes in circulation and pressure from the baby on nerves and blood vessels are possible causes of leg cramps during pregnancy.
