Abstract
The monitoring of body mass (BM) plasma sodium concentration ([Na+]) and urinary specific gravity (U-sg) are com-monly used to help detect and prevent over- or dehydration in endurance athletes. We investigated pre-and post-race hydration status in 113 amateur 24-h ultra-runners, 100-km ultra-runners, multi-stage mountain bikers and 24-h mountain bikers, which drank ad libitum without any intervention and compared results of hyponatremic and non-hyponatremic finishers.
On average, pre-race plasma [Na+] and both pre- and post-race levels of U-sg and BM were not significantly different between both groups. However, nearly 86% of the post-race hyponatremic (exercise-associated hyponatremia, EAH) and 68% of the normonatremic (non-EAH) ultra-athletes probably drank prior the race greater volumes than their thirst dictated regarding to individual pre race U-sg levels.
Fluid intake during the race was equal and was not related to plasma [Na+], U-sg or BM changes. A significant decrease in post-race plasma [Na+], BM and an increasement in post-race U-sg was observed in EAH and non-EAH finishers.
Moreover, pre-race plasma [Na+] was inversely associated with post-race percentage change in plasma [Na+], and pre-race U-sg and urinary [Na+] with percentage change in U-sg in both groups with and without post-race EAH. Thirteen (11.5%) finishers developed post-race EAH (plasma [Na+] < 135 mM).
The incidence of EAH in ultra-endurance athletes competing in the Czech Republic was higher than reported previously.