Muscle cramps are a common and usually harmless condition where the muscle suddenly becomes tight and painful, from a few seconds to 10 minutes. It usually occurs in the calf muscles, although it can affect any part of your leg, including your feet and thighs.
Source: Leg cramps @ NHS Choices
- Muscle spasms and cramps @ WebMD
Excerpt: Cramps are caused by muscle spasms, involuntary contractions of one or more muscles. In addition to the foot and calf muscles, other muscles prone to spasms include the front and back of the thigh, the hands, arms, abdomen and muscles along the ribcage. Almost everyone experiences muscle cramps, which come without warning. What causes them, and what can you do to relieve them?