Prevalence of Exercise-Associated Hyponatremia in Male Ultraendurance Athletes

Abstract

The prevalence of exercise-associated hyponatremia (EAH) has mainly been investigated in marathoners and Ironman triathletes. The aim of this study was to investigate the prevalence of EAH in male ultraendurance athletes in other disciplines, such as ultraswimming, ultracycling, and ultramarathon running. Observational field study. "Marathon Swim" in Lake Zurich, the "Swiss Cycling Marathon," the "Swiss Bike Masters," the "100-km Lauf Biel," and the "Swiss Jura Marathon." Fifteen ultraswimmers, 28 ultra-road cyclists, 37 ultra-mountain bikers, 95 ultramarathoners, and 25 mountain ultramarathoners. Changes in body mass, plasma sodium, urinary specific gravity, and hematocrit were measured. The athletes recorded their intake of fluids. Two swimmers (13%), 3 road cyclists (10.7%), no mountain bikers (0%), 5 ultramarathoners (5%), and 2 mountain ultramarathoners (8%) developed EAH. In the mountain bikers (r = -0.41) and the 100-km ultramarathoners (r = -0.52), fluid intake was significantly and negatively related to race time. In the mountain ultramarathoners, fluid consumption increased during the race. The prevalence of EAH was no higher in ultraendurance athletes compared with existing reports on marathoners and Ironman triathletes. Of the 200 investigated ultraendurance athletes, 12 finishers (6%) developed EAH.