Exercise-Associated Hyponatremia and Hydration Status in 161-km Ultramarathoners
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.
Hoffman, Martin D., Tamara Hew-Butler, and Kristin J. Stuempfle. “Exercise-Associated Hyponatremia and Hydration Status in 161-km Ultramarathoners.” Medicine and Science in Sports and Exercise 45.4 (2013): 784-791.