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

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