Can changes in body mass and total body water accurately predict hyponatremia after a 161-km running race?

Objective: To relate changes in body mass, total body water (TBW), extracellular fluid (ECF), and serum sodium concentration ([Na]) from a 161-km ultramarathon to finish time and incidence of hyponatremia.

Design: Observational.

Setting: : The 2008 Rio Del Lago 100-Mile (161-km) Endurance Run in Granite Bay, California.