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Br J Sports Med 39:e38 doi:10.1136/bjsm.2005.018820
  • Electronic pages

Hyponatraemic encephalopathy despite a modest rate of fluid intake during a 109 km cycle race

  1. J P Dugas1,
  2. T D Noakes1
  1. 1UTC/MRC Research Unit for Exercise Science and Sports Medicine, University of Cape Town, Sports Science Institute of South Africa, Cape Town, South Africa
  1. Correspondence to:
 J P Dugas
 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; jdugassports.uct.ac.za
  • Accepted 30 March 2005

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.

Footnotes

  • Competing interests: none declared

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