Most people have experienced a cramp (also known as a charley horse). It occurs when, out of the blue, a muscle contracts violently and will not let go until it is good and ready.
A cramp usually comes as a surprise and can drop even the strongest athlete to their knees. Cramps can happen during or after exercise – up to six hours later – and during sleep (called night cramps). A cramp can last mere seconds or up to 10 minutes, and the muscle can be sore up to 24 hours later.