No case of exercise-associated hyponatraemia in top male ultra-endurance cyclists: the 'Swiss Cycling Marathon'

Eur J Appl Physiol. 2012 Feb;112(2):689-97. doi: 10.1007/s00421-011-2024-y. Epub 2011 Jun 9.


The prevalence of exercise-associated hyponatraemia (EAH) has been investigated in endurance athletes such as runners and Ironman triathletes, but not in ultra-endurance road cyclists. We assessed fluid intake and changes in body mass, urine specific gravity and plasma sodium concentration ([Na(+)]) in 65 ultra-endurance road cyclists in a 720-km ultra-cycling marathon, the 'Swiss Cycling Marathon'. The cyclists lost 1.5 (1.7)% body mass (P < 0.01). No athlete developed EAH. Fluid intake was associated with the change in plasma [Na(+)] (r = -0.32, P < 0.05) and the change in body mass (r = -0.30, P < 0.05). The change in plasma [Na(+)] was related to post-race plasma [Na(+)] (r = 0.63, P < 0.0001). To conclude, ad libitum fluid intake in ultra-endurance cyclists in a single-stage ultra-endurance road cycling race showed no case of EAH. Future studies regarding drinking behaviour in different ultra-endurance disciplines might give insights into why the prevalence of EAH is different in the different disciplines.

MeSH terms

  • Bicycling*
  • Humans
  • Hyponatremia / epidemiology*
  • Hyponatremia / physiopathology*
  • Male
  • Middle Aged
  • Physical Endurance*
  • Prevalence
  • Switzerland / epidemiology
  • Water-Electrolyte Balance*