title: Prevalence of exercise-associated hyponatremia in male ultraendurance athletes.
abstract: OBJECTIVE
  The prevalence of exercise-associated hyponatremia (EAH) has mainly been investigated in marathoners and Ironman triathletes. The aim of this study was to investigate the prevalence of EAH in male ultraendurance athletes in other disciplines, such as ultraswimming, ultracycling, and ultramarathon running.
  
  
  METHODS
  Observational field study.
  
  
  METHODS
  "Marathon Swim" in Lake Zurich, the "Swiss Cycling Marathon," the "Swiss Bike Masters," the "100-km Lauf Biel," and the "Swiss Jura Marathon."
  
  
  METHODS
  Fifteen ultraswimmers, 28 ultra-road cyclists, 37 ultra-mountain bikers, 95 ultramarathoners, and 25 mountain ultramarathoners.
  
  
  METHODS
  Changes in body mass, plasma sodium, urinary specific gravity, and hematocrit were measured. The athletes recorded their intake of fluids.
  
  
  RESULTS
  Two swimmers (13%), 3 road cyclists (10.7%), no mountain bikers (0%), 5 ultramarathoners (5%), and 2 mountain ultramarathoners (8%) developed EAH. In the mountain bikers (r = -0.41) and the 100-km ultramarathoners (r = -0.52), fluid intake was significantly and negatively related to race time. In the mountain ultramarathoners, fluid consumption increased during the race.
  
  
  CONCLUSIONS
  The prevalence of EAH was no higher in ultraendurance athletes compared with existing reports on marathoners and Ironman triathletes. Of the 200 investigated ultraendurance athletes, 12 finishers (6%) developed EAH.
authors.affiliation: Gesundheitszentrum St. Gallen, St. Gallen, Switzerland; Institute of General Practice and Health Services Research, University of Zurich, Zurich, Switzerland. beat.knechtle@hispeed.ch
authors.forename: Beat
authors.initials: B
authors.lastname: Knechtle
authors.forename: Markus
authors.initials: M
authors.lastname: Gnädinger
authors.forename: Patrizia
authors.initials: P
authors.lastname: Knechtle
authors.forename: Reinhard
authors.initials: R
authors.lastname: Imoberdorf
authors.forename: Götz
authors.initials: G
authors.lastname: Kohler
authors.forename: Peter
authors.initials: P
authors.lastname: Ballmer
authors.forename: Thomas
authors.initials: T
authors.lastname: Rosemann
authors.forename: Oliver
authors.initials: O
authors.lastname: Senn
mesh_terms: D000328:Adult; D056352:Athletes; D001642:Bicycling / Q000502:physiology* / Q000706:statistics & numerical data; D015992:Body Mass Index; D006801:Humans; D007010:Hyponatremia / Q000453:epidemiology* / Q000209:etiology; D008297:Male; D008875:Middle Aged; D010807:Physical Endurance / Q000502:physiology*; D015995:Prevalence; D012420:Running / Q000502:physiology* / Q000706:statistics & numerical data; D013550:Swimming / Q000502:physiology* / Q000706:statistics & numerical data