Waking suddenly with a painfully tightened calf can be frightening. One moment, you are sleeping peacefully; the next, an intense muscle spasm jolts you awake, leaving your leg feeling as though it has twisted into a hard, painful knot.
These episodes are medically known as nocturnal leg cramps. They are sudden, involuntary muscle contractions that occur while a person is resting or sleeping. Although the calf muscles are most commonly affected, cramps can also develop in the feet, thighs, and other leg muscles.
A cramp may last anywhere from a few seconds to several minutes. Even after the muscle finally relaxes, tenderness, stiffness, or soreness can linger for hours and sometimes continue into the following day.
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