title: Hyponatraemic encephalopathy despite a modest rate of fluid intake during a 109 km cycle race.
abstract: OBJECTIVE
  To report a case of exertional hyponatraemic encephalopathy that occurred despite a modest rate of fluid intake during a 109 km cycling race.
  
  
  METHODS
  Men and women cyclists were weighed before and after the race. All subjects were interviewed and their water bottles measured to quantify fluid ingestion. A blood sample was drawn after the race for the measurement of serum Na(+) concentration.
  
  
  RESULTS
  From the full set of data (n = 196), one athlete was found to have hyponatraemic encephalopathy (serum [Na(+)] 129 mmol/l). She was studied subsequently in the laboratory for measurement of sweat [Na(+)] and sweat rate.
  
  
  CONCLUSIONS
  Despite a modest rate of fluid intake (735 ml/h) and minimal predicted sweat Na(+) losses, this female athlete developed hyponatraemic encephalopathy. The rate of fluid intake is well below the rate currently prescribed as optimum. Drinking to thirst and not to a set hourly rate would appear to be the more appropriate behaviour.
authors.affiliation: UTC/MRC Research Unit for Exercise Science and Sports Medicine, University of Cape Town, Sports Science Institute of South Africa, PO Box 115, Newlands 7725, Cape Town, South Africa. jdugas@sports.uct.ac.za
authors.forename: J P
authors.initials: JP
authors.lastname: Dugas
authors.forename: T D
authors.initials: TD
authors.lastname: Noakes
mesh_terms: D001642:Bicycling / Q000502:physiology*; D001928:Brain Diseases, Metabolic / Q000209:etiology*; D004326:Drinking / Q000502:physiology*; D015444:Exercise / Q000502:physiology; D005260:Female; D006801:Humans; D007010:Hyponatremia / Q000209:etiology*; D008875:Middle Aged; D015430:Weight Gain