Dehydration and hyponatremia during triathlons.

In ultraendurance triathlons, dehydration and electrolyte balance are important factors in race completion and level of performance. Dehydration is the most common reason for a triathlete in the Hawaii Ironman Triathlon to need medical assistance. Hyponatremia is the predominant electrolyte disturbance. We have previously described exercise-induced hyponatremia and documented its incidence as a function of race length and state of hydration. This syndrome, dehydration plus hyponatremia, is extremely rare in races lasting less than 4 h but becomes common in races lasting longer than 8 h. Recommendations are made to help ultraendurance athletes understand and maintain proper fluid and electrolyte balance.