The incidence of hyponatremia in prolonged exercise activity.

Hyponatremia is a medical condition characterized by decreased concentration of sodium in the blood, which may occur in participants in endurance and ultraendurance athletic events. Slower competitors and nonacclimatized individuals appear to be at greater risk of becoming hyponatremic, especially if they experience salt depletion as a result of sweating or water intoxication. Clinical signs and symptoms of hyponatremia, which can range from muscle cramps and mental confusion to convulsions and coma, may not manifest themselves until well after the end of the event. Death may occur if hyponatremia is not properly diagnosed and treated. Medical personnel treating this condition should be cautious not to confuse water intoxication with dehydration, which produces similar symptoms. To prevent hyponatremia, participants should acclimatize themselves to race conditions prior to the event. In addition, endurance athletes should be encouraged to ingest low sodium concentrate drinks during events lasting longer than 4 hours.