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

Abstract

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. Abstract The prevalence of exercise-associated hyponatraemia (EAH) has been investigated in endurance athletes such as runners and Ironman triathletes, but not in ultraendurance 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.

Statement of the 3rd International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015

“…The reported incidence of asymptomatic EAH has ranged from 0%30 53 to 51%54 immediately post-race. In a study of an ultramarathon, 67% of the participants were hyponatraemic (asymptomatic) at some point during the race, but only 27% finished the race with serum [Na + ] <135 mmol/L (40% self-corrected prior to finishing the event) 11.…”

“…The incidence of asymptomatic EAH in Ironman triathlons in different environments has been reported to range from negligible,10 to as high as 18%57 and 25% 19. In studies on endurance cyclists, the incidence of asymptomatic EAH has ranged from 0% in a 720 km race,30 to 12% in a 109 km race 15. In a 26.4 km swim, 17% of swimmers developed asymptomatic hyponatraemia 32.…”

“…Asymptomatic EAH represents a biochemical finding, diagnosed by blood electrolyte testing for research or unrelated metabolic screening purposes 10 15 18 19 28 30 32 53–59. This group of participants presents without any discernable symptoms, or may have mild, generalised and transient symptoms commonly experienced by other participants who do not typically seek medical care following exercise.…”

“…Asymptomatic hyponatraemia is not normally detected unless an athlete has blood electrolyte concentrations tested for some other reason 10 15 18 19 28 30 32 53–59. In athletes with this incidental biochemical diagnosis, oral or intravenous hypotonic fluid intake should be restricted until the onset of urination (which suggest that AVP levels have fallen and that the urine is likely dilute) to reduce the risk of further decreasing [Na + ] with continued AVP-mediated water retention 5 6 120.…”

Energy Balance, Macronutrient Intake, and Hydration Status During a 1,230 km Ultra-Endurance Bike Marathon

“…Other studies have reported slightly higher fluid intake (530 to 670 ml/hr), but also no increased incidence of dehydration based on plasma volume changes and USG during other ultra-endurance events (Neumayr et al, 2003(Neumayr et al, , 2005Rüst et al, 2012).…”