European Journal of Applied Physiology

, Volume 98, Issue 1, pp 62–70 | Cite as

Effect of altered pre-exercise carbohydrate availability on selection and perception of effort during prolonged cycling

  • N. A. Johnson
  • S. R. Stannard
  • P. G. Chapman
  • M. W. Thompson
Original Article


This study assessed the effect of altered carbohydrate (CHO) availability on self-selected work rate during prolonged time-trial cycling. Eight endurance-trained men undertook two experimental cycling time-trials after glycogen-depleting exercise and 2 days of: (a) high (9.3 ± 0 g CHO kg−1 day−1) (HC) and (b) low CHO intakes (0.6 ± 0.1 g CHO kg−1 day−1) (LC), via a double-blinded crossover design. All feedback regarding performance was removed during both exercise trials. Self-selected external power output was not different during the first 2 h of exercise between experimental conditions (P > 0.05), despite reported sensations of increased tiredness before and during exercise, significantly reduced whole body CHO oxidation (P < 0.05), plasma lactate concentrations (P < 0.05) and earlier onset of fatigue during exercise in LC versus HC. Perceived exertion was not different throughout exercise between conditions (P > 0.05). Mean power output declined significantly in LC versus HC (P < 0.05) after ∼ 2 h of exercise, and was associated with significant reductions in cadence, heart rate and plasma glucose concentration (P < 0.05). These results demonstrate that when compared with time-trial cycling performed after a HC diet, reduced CHO availability does not initially alter self-selected work rate in endurance athletes who are deceived of their CHO status prior to exercise. This finding suggests that reduced work rate during exercise following lowered CHO intake may, in part, be a consequence of the subject’s awareness of dietary CHO restriction rather than solely a physiologically mediated action. Further research is required to distinguish the influence of circulating glucose and peripheral glycogen availability on pacing strategy during prolonged exercise.


Endurance exercise High fat diet Perceived exertion Fatigue Pacing strategy 



The authors wish to thank Kirsty Mehalski for her help with data collection and Pat Ruell for her technical assistance.


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Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  • N. A. Johnson
    • 1
    • 2
  • S. R. Stannard
    • 1
  • P. G. Chapman
    • 1
  • M. W. Thompson
    • 1
  1. 1.The School of Exercise and Sport ScienceThe University of SydneyLidcombeAustralia
  2. 2.School of Human Life SciencesUniversity of TasmaniaLauncestonAustralia

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