No Case of Exercise-Associated Hyponatremia in Male Ultra-Endurance Mountain Bikers in the 'Swiss Bike Masters'

10.4077/CJP.2011.AMM050

Beat Knechtle；Patrizia Knechtle；Thomas Rosemann

fluid intake ； electrolyte disorder ； plasma sodium ； body mass changes

The Chinese Journal of Physiology

54卷6期（2011 / 12 / 01）

2 - 7

英文

Exercise-associated hyponatremia (EAH) has mainly been investigated in runners and triathletes. In mountain bikers, EAH was studied in two multi-stage races, but not in a single stage race. The aim of this study was to investigate the prevalence of EAH in a single-stage mountain bike ultra-marathon. In the 'Swiss Bike Masters' over 120 km with a climb of ~ 5,000 m in altitude, we determined pre and post race body mass, hematocrit, plasma sodium concentration ([Na(superscript +)]), and urinary specific gravity in 37 cyclists. Athletes recorded their fluid intake while racing. No athlete developed EAH. The cyclists drank on average (means ± SD) 0.7 ± 0.2 l/h. Fluid intake was significantly and negatively related to race time (r = -0.41, P ＜ 0.05), but showed no association with post race plasma [Na(superscript +)], the change in plasma [Na(superscript +)], post race body mass, or the change in body mass. The athletes lost 1.4 kg body mass (P ＜ 0.05), plasma [Na(superscript +)] decreased by 0.7% (P ＜ 0.05), plasma volume increased by 1.4% and urinary specific gravity increased by 0.4% (P ＜ 0.05). The change in body mass was neither related to post race plasma [Na(superscript +)] nor to the change in plasma [Na(superscript +)]. The decrease in plasma [Na(superscript +)] was not related to fluid intake. The change in plasma [Na(superscript +)] was related to post race plasma [Na(superscript +)] (r = 0.40, P ＜ 0.01). Ad libitum fluid intake showed no case of EAH in a single-stage mountain bike ultra-marathon. In contrast to previous findings, the faster athletes drank more than the slower ones.

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