title: Hyperthermic fatigue precedes a rapid reduction in serum sodium in an ironman triathlete: a case report.
abstract: OBJECTIVE
  To monitor the hydration, core temperature, and speed (pace) of a triathlete performing an Ironman triathlon.
  
  
  METHODS
  A 35-year-old experienced male triathlete participated in the Western Australian Ironman triathlon on December 1, 2006. The participant was monitored for blood Na(+) concentration before the race (PRE), at the transitions (T1 and T2), halfway through the run (R21), and after the race (POST; 2hPOST). Core body temperature (T(c); pill telemetry) was recorded continuously, and running speed (s3 stride sensor) was measured during the run.
  
  
  RESULTS
  The participant completed the race in 11 h 38 min, in hot conditions (26.6 +/- 5.8 degrees C; 42 +/- 19% rel. humidity). His T(c) increased from 37.0 to 38.6 degrees C during the 57-min swim, and averaged 38.4 degrees C during the 335-min bike (33.5 km x h(-1)). After running at 12.4 km x h(-1) for 50 min in the heat (33.1 degrees C), T(c) increased to 39.4 degrees C, before slowing to 10.0 km x h(-1) for 20 min. T(c) decreased to 38.9 degrees C until he experienced severe leg cramps, after which speed diminished to 6 km x h(-1) and T(c) fell to 38.0 degrees C. The athlete's blood Na(+) was constant from PRE to T2 (139-140 mEq x L(-1), but fell to 131 mEq x L(-1) at R21, 133 mEq x L(-1) at POST, and 128 mEq x L(-1) at 2hPOST. The athlete consumed 9.25 L of fluid from PRE to T2, 6.25 L from T2 to POST, and lost 2% of his body mass, indicating sweat losses greater than 15.5 L.
  
  
  CONCLUSIONS
  This athlete slowed during the run phase following attainment of a critically high T(c) and experienced an unusually rapid reduction in blood Na(+) that preceded cramping, despite presenting with signs of dehydration.
authors.affiliation: School of Exercise, Biomedical and Health Sciences, Edith Cowan University, Joondalup, Australia.
authors.forename: Paul B
authors.initials: PB
authors.lastname: Laursen
authors.forename: Greig
authors.initials: G
authors.lastname: Watson
authors.forename: Chris R
authors.initials: CR
authors.lastname: Abbiss
authors.forename: Bradley A
authors.initials: BA
authors.lastname: Wall
authors.forename: Kazunori
authors.initials: K
authors.lastname: Nosaka
mesh_terms: D000328:Adult; D000450:Aldosterone / Q000097:blood; D054874:Athletic Performance / Q000502:physiology; D001642:Bicycling / Q000502:physiology; D001831:Body Temperature / Q000502:physiology; D003681:Dehydration / Q000503:physiopathology; D004326:Drinking / Q000502:physiology; D005221:Fatigue / Q000503:physiopathology*; D005334:Fever / Q000503:physiopathology*; D006801:Humans; D008297:Male; D009120:Muscle Cramp / Q000503:physiopathology; D009994:Osmolar Concentration; D012420:Running / Q000502:physiology; D012964:Sodium / Q000097:blood*; D013546:Sweating / Q000502:physiology; D013550:Swimming / Q000502:physiology; D014556:Urine / Q000502:physiology
chemical_list: D000450:Aldosterone; D012964:Sodium