title: Change in serum sodium concentration during a cold weather ultradistance race.
abstract: OBJECTIVE
  To investigate change in serum sodium concentration and its potential causes during a cold weather ultradistance race.
  
  
  METHODS
  Descriptive research.
  
  
  METHODS
  A 100-mile (161-km) race over a snow-packed course in the Alaskan wilderness. Athletes competed in 1 of 3 divisions: foot, bike, or ski.
  
  
  METHODS
  Twenty athletes (11 runners, 6 cyclists, 3 skiers) volunteered for the study.
  
  
  METHODS
  None.
  
  
  METHODS
  Subjects were weighed and had blood drawn for hematocrit, serum sodium, serum aldosterone, and plasma arginine vasopressin concentrations pre- and postrace. Fluid and sodium intake were determined by race dietary analysis.
  
  
  RESULTS
  Serum sodium concentration decreased significantly prerace (140.8 +/- 1.2 mmol/L) to postrace (138.4 +/- 2.2 mmol/L), although no athletes were classified as hyponatremic. Mean weight loss was significant during the race (-1.2 kg), although 1 athlete maintained his weight, and 3 athletes gained small amounts of weight (0.2 kg, 0.2 kg, and 0.5 kg, respectively). Hematocrit decreased significantly prerace (42.2 +/- 3.5) to postrace (40.3 +/- 4.1). Plasma arginine vasopressin and serum aldosterone increased significantly during the race (2.6 +/- 0.7 to 6.0 +/- 4.6 pg/mL and 5.1 +/- 2.6 to 40.8 +/- 25.1 ng/dL, respectively). Fluid consumption was 300 +/- 100 mL/h, and sodium intake was 310 +/- 187 mg/h.
  
  
  CONCLUSIONS
  Decreased serum sodium concentration after a cold weather ultradistance race was due to fluid overload caused by excessive fluid consumption. Current recommendations that ultradistance athletes consume 500 to 1000 mL/h may be too high for athletes competing in the extreme cold.
authors.affiliation: Health and Exercise Sciences Department, Gettysburg College, Pennsylvania 17325, USA. kstuempf@gettysburg.edu
authors.forename: Kristin J
authors.initials: KJ
authors.lastname: Stuempfle
authors.forename: Donald R
authors.initials: DR
authors.lastname: Lehmann
authors.forename: H Samuel
authors.initials: HS
authors.lastname: Case
authors.forename: Sherri Lind
authors.initials: SL
authors.lastname: Hughes
authors.forename: Deborah
authors.initials: D
authors.lastname: Evans
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D000450:Aldosterone / Q000097:blood; D001127:Arginine Vasopressin / Q000097:blood; D001642:Bicycling / Q000502:physiology*; D001835:Body Weight / Q000502:physiology; D003080:Cold Temperature; D004032:Diet; D004326:Drinking / Q000502:physiology; D005260:Female; D006400:Hematocrit; D006801:Humans; D008297:Male; D010807:Physical Endurance / Q000502:physiology; D012420:Running / Q000502:physiology*; D012865:Skiing / Q000502:physiology*; D012964:Sodium / Q000008:administration & dosage / Q000097:blood*; D014882:Water-Electrolyte Balance / Q000502:physiology
chemical_list: D001127:Arginine Vasopressin; D000450:Aldosterone; D012964:Sodium