title: Do male 100-km ultra-marathoners overdrink?
abstract: OBJECTIVE
  Fluid overload is considered a main risk factor for exercise-associated hyponatremia (EAH). The aim of this study was to investigate the incidence of EAH in ultra-runners at the 100 km ultra-run in Biel, Switzerland.
  
  
  METHODS
  Pre- and postrace, body mass, urinary specific gravity, hemoglobin, hematocrit, plasma [Na+], and plasma volume were determined.
  
  
  RESULTS
  Of the 145 finishers, seven runners (4.8%) developed asymptomatic EAH. While running, the athletes consumed a total of (median and interquartile ranges) 6.9 (5.1-8.8) L over the 100 km distance, equal to 0.58 (0.41-0.79) L/h. Fluid intake correlated negatively and significantly with race time (r = -.50, P < .0001). Body mass decreased, plasma [Na+] remained unchanged, hematocrit and hemoglobin decreased, and urinary specific gravity increased. Plasma volume increased by 4.6 (-2.3 to 12.8) %. Change in body mass correlated with both postrace plasma [Na+] and Δ plasma [Na+]. Postrace plasma [Na+] correlated to Δ plasma [Na+]. Fluid intake was associated neither with postrace plasma [Na+] nor with Δ plasma [Na+]. Fluid intake was related to Δ body mass (r = .21, P = .012), but not to postrace body mass. Fluid intake showed no correlation to Δ plasma volume. Change in plasma volume was associated with postrace [Na+].
  
  
  CONCLUSIONS
  Incidences of EAH in 100 km ultra-marathoners were lower compared with reports on marathoners. Body mass decreased, plasma volume increased, and plasma [Na+] was maintained. Since fluid intake was related neither to Δ plasma volume nor to Δ plasma [Na+], we assume that factors other than fluid intake maintained body fluid homeostasis.
authors: Gesundheitszentrum St. Gallen, St. Gallen, Switzerland.
authors: Beat
authors: B
authors: Knechtle
authors: Patrizia
authors: P
authors: Knechtle
authors: Thomas
authors: T
authors: Rosemann
mesh_terms: D001835:Body Weight; D004327:Drinking Behavior / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D006801:Humans; D007010:Hyponatremia / Q000453:epidemiology / Q000503:physiopathology*; D008297:Male; D010953:Plasma Volume; D012420:Running / Q000502:physiology*