Exercise-Associated Hyponatremia in an Ultra-Endurance Mountain Biker: A Case Report

Symptomatic exercise-associated hyponatremia (EAH), which is relatively common among marathon runners, is an uncommon event among ultra-endurance athletes. A 44-year-old man presented to the emergency department with increased thirst after successfully completing a 100-mile mountain bike race in Leadville, Colorado. Initial laboratory tests revealed a blood sodium level of 116 mEq/L. The primary etiologic factor in EAH is fluid consumption in excess of fluid losses in prolonged exertion. Early diagnosis and management is crucial to prevent cerebral and pulmonary edema.