title: Body Weight, Serum Sodium Levels, and Renal Function in an Ultra-Distance Mountain Run.
abstract: OBJECTIVE
  To determine body weight and serum [Na] changes in runners completing an 85-km mountain run, particularly with reference to their "in-race" hydration protocols.
  
  
  METHODS
  Prospective observational cohort study.
  
  
  METHODS
  Cradle Mountain Run, Tasmania, Australia, February 2011.
  
  
  METHODS
  Forty-four runners (86% of starters) prospectively enrolled, with 41 runners (80% of starters) eligible for inclusion in final data set.
  
  
  METHODS
  Body weight change, serum sodium concentration change, and hydration plan (according to thirst vs preplanned fluid consumption).
  
  
  RESULTS
  There was 1 case of exercise-associated hyponatremia (EAH) [postrace [Na], 132 mmol/L]. This runner was asymptomatic. There was a strongly significant correlation between the change in serum [Na] and body weight change during the race. There was a significant inverse correlation between serum [Na] and volume of fluid consumed. Change of serum [Na] was not correlated with the proportion of water versus electrolyte drink consumed. Runners drinking to thirst consumed significantly lower average fluid volumes and had higher postrace serum [Na] than those complying with a preplanned hydration protocol (142 mmol/L vs 139 mmol/L). More experienced runners tended to drink to thirst.
  
  
  CONCLUSIONS
  There was a 2% incidence of EAH in this study. Serum [Na] change during an 85-km mountain run was inversely correlated with the volume of fluid consumed. The results provide further evidence that EAH is a dilutional hyponatremia caused by excessive consumption of hypotonic fluids. Drinking to thirst represents a safe hydration strategy for runners in a wilderness environment.
  
  
  CONCLUSIONS
  Drinking to thirst during endurance running events should be promoted as a safe hydration practice.
authors.affiliation: *Olympic Park Sports Medicine Centre, Melbourne, Australia; and †The Sports Medicine Practice, Hobart, Australia.
authors.forename: Bianca
authors.initials: B
authors.lastname: Scotney
authors.forename: Steve
authors.initials: S
authors.lastname: Reid
mesh_terms: D000328:Adult; D000368:Aged; D001835:Body Weight; D015331:Cohort Studies; D004327:Drinking Behavior; D060766:Drinking Water; D004573:Electrolytes; D005260:Female; D006801:Humans; D007010:Hyponatremia / Q000097:blood / Q000453:epidemiology*; D015994:Incidence; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012420:Running; D012964:Sodium / Q000097:blood*; D013648:Tasmania / Q000453:epidemiology; D013894:Thirst; D014882:Water-Electrolyte Balance; D055815:Young Adult
chemical_list: D060766:Drinking Water; D004573:Electrolytes; D012964:Sodium