Exercise-Associated Hyponatremia and Hydration Status in 161-km Ultramarathoners

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Department 1

Health Sciences


Purpose: This work combines and reanalyzes 5 yr of exercise-associated hyponatremia (EAH) research at 161-km ultramarathons in northern California with primary purposes to define the relationship between postrace blood sodium concentration ([Na+]) and change in body weight; to examine the interactions among EAH incidence, ambient temperature, and hydration state; and to explore the effect of hydration status on performance.

Methods: Prerace and postrace body weight and finish time data were obtained on 887 finishers, and postrace [Na+] was also obtained on a subset of 669 finishers.

Results: EAH incidence was 15.1% overall (range, 4.6%-51.0% by year) and had a significant positive relationship with ambient temperature. Of the runners with EAH, 23.8% were classified as overhydrated (weight change, >= 0), 40.6% were euhydrated (weight change,

Conclusions: EAH incidence can be high in 161-km ultramarathons in northern California. In this environment, EAH is more common with dehydration than overhydration and is more common in hotter ambient temperature conditions. Because weight loss >3% does not seem to have an adverse effect on performance, excessive sodium supplementation and aggressive fluid ingestion beyond the dictates of thirst are ill advised.


Original version is available from the publisher at: http://www.acsm.org/access-public-information/acsm-journals/medicine-science-in-sports-exercise



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