Rates of fluid ingestion alter pacing but not thermoregulatory responses during prolonged exercise in hot and humid conditions with appropriate convective cooling

  • J. P. DugasEmail author
  • U. Oosthuizen
  • R. Tucker
  • T. D. Noakes
Original Article


The aim of the study was to examine the effects of fluid replacement on thermoregulation and cycling performance in hot, humid conditions. Six male cyclists (PPO = 426 ± 39 W) performed six 80 km time trials. Subjects replaced 0% (0); 33% (33); 66% (66); or 100% (100) of the weight lost during an “ad libitum” trial (Ad Lib). In another condition (WET), subjects rinsed their mouths at 10 km intervals. There was no trial effect on any thermoregulatory variables or on performance. When WET, 0, 33 (“LO”) were compared to Ad Lib; 66, 100 (“HI”), power output was higher in HI (209 ± 22 vs. 193 ± 22 W, p < 0.05). Restricting fluid below ad libitum rates impaired performance (LO group). Rates greater than ad libitum did not result in further improvements. Ad libitum fluid ingestion is optimal as it prevents athletes from ingesting too little or too much fluid.


Heat Rectal temperature Temperature Cycling Performance Exercise Time trial Dehydration Anticipatory regulation Fluid balance 



We would like to acknowledge the subjects in this study for all their extraordinary commitments and for their continued support of this unit’s research. This research was funded in part by Discovery Health, The National Research Foundation of South Africa’s Technology and Human Resources for Industry Program (THRIP), Bromor Foods, and the Harry Crossley and Nelly Atkinson staff research funds of the University of Cape Town.

Conflict of interest statement

The authors have no conflicts of interest with this study and its results.


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Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  • J. P. Dugas
    • 1
    • 2
    Email author
  • U. Oosthuizen
    • 1
  • R. Tucker
    • 1
  • T. D. Noakes
    • 1
  1. 1.UCT/MRC Research Unit for Exercise Science and Sports Medicine, Department of Human BiologyUniversity of Cape Town, Sports Science InstituteCape TownSouth Africa
  2. 2.ChicagoUSA

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