A charley horse is an American term for a very painful involuntary cramp, most commonly occurring in the legs (usually located in the calf muscle) and/or foot, lasting anywhere from a few seconds to a couple of days.
A dead leg often occurs in contact sports, such as football, when an athlete suffers a knee or other blunt trauma to the lateral quadriceps causing a haematoma or temporary paresis and antalgic gait as a result of pain.
The origination of the phrase is credited to two baseball players, Jack Glasscock and Joe Quest.
[4] Charley horses have many possible causes directly resulting from high or low pH or substrate concentrations in the blood, including hormonal imbalances, dehydration, low levels of magnesium, potassium, or calcium (evidence has been mixed),[5][6][7] side effects of medication, or, more seriously, diseases such as amyotrophic lateral sclerosis and neuropathy.
[8] Charley horses seem to be most common in individuals who engage in strenuous physical activities, such as those who work in construction or play sports.