When the muscle in a person's leg contracts on its own and remains contracted, it is known as a cramp. The most common cause of leg cramps is overuse of the muscle, such as when a person exercises too much. A person is usually also dehydrated when he overuses the leg muscles, furthering the risk of cramps. Injury to the muscle is another common cause of leg cramps, as is a lack of certain minerals. In some cases, such as night leg cramps, the cause of leg cramps is unknown.
A leg cramp can signal to a person that he is not getting enough nutrients. If someone doesn't have enough calcium in his blood, his legs may cramp as calcium helps the muscles contract properly. A person taking diuretics, or water pills, for high blood pressure may not have enough potassium, which is another cause of leg cramps. Low levels of magnesium or vitamin E can also cause leg cramps.
A lot of exercise or activity is perhaps the most common cause of leg cramps, particularly in older people. Someone can experience a cramp in the calf from swimming or an upper leg cramp after running. Leg cramps may occur after exercise if a person is not used to exercising and did not take in enough water during the activity. If someone exercises in hot weather and does not drink enough water during the activity, leg cramps may be the first sign that she is suffering from heat stroke.
Injury to the leg muscle or to the nerves surrounding the muscle is another cause of leg cramps. If someone breaks his leg, the muscles may cramp around the broken bone in an attempt to hold the bone steady and prevent excessive movement. Irritation of the nerves around the muscle may also cause a cramp in the leg.
Cramps can also occur when a person stands on a hard surface for a long period of time. Sitting for too long or lying with the legs in an awkward position can also cause them to cramp. People with flat feet may be more likely to suffer from leg cramps.
Leg cramps can be avoided by staying hydrated during exercise and by eating a diet high in nutrients such as calcium and potassium. A person should drink at least half a liter of water three hours before exercising. During exercise, she should drink a sports drink or a beverage containing electrolytes such as sodium and potassium. Stretching before working out can also keep cramps away.