Heat cramps

[Rihanna]

Heat cramps are severe muscle spasms resulting from a combination of prolonged exercise, heavy sweating, and excessive water replacement in extreme heat.
(See also Overview of Heat Disorders.)
Heat cramps is a mild type of heat disorder that tends to occur in healthy people who are active in the heat.
During sweating, salts (electrolytes) and fluids are lost, but drinking large quantities of water dilutes the salts, causing cramps. Heavy sweating is most likely to occur on warm days, especially during or after strenuous exertion. Heat cramps are common among all of the following:

Manual laborers, such as engine-room personnel, steelworkers, roofers, and miners
Athletes, especially mountain climbers or skiers, whose many layers of clothing may keep them from noticing their heavy sweating, and tennis players and runners who do not take time to replace salts lost in sweat
Military trainees

Heat cramps are strong contractions in muscles of the hands, calves, feet, thighs, or arms. The contractions cause muscles to become hard, tense, and painful. The pain can be mild to intense. Fever does not typically occur.
Mild heat cramps can be treated by having the person rest in a cool environment and drink beverages that contain salt or eat salty food. Drinking 1 to 2 quarts (about 1 to 2 liters) of a sports drink or water containing 2 teaspoons of salt is usually enough. Severe heat cramps are treated with fluids and salts given by vein (intravenously). Stretching the involved muscle often gives immediate relief of pain.