Leading Article

Sports Medicine

, Volume 24, Issue 2, pp 73-81

Carbohydrate-Loading and Exercise Performance

An Update
  • John A. HawleyAffiliated withSports Science Institute of South Africa, incorporating the Liberty Life Chair of Exercise and Sports Science, the Medical Research Council and the University of Cape Town Bioenergetics of Exercise Research Unit, Department of Physiology, University of Cape Town Medical School Email author 
  • , Elske J. SchabortAffiliated withSports Science Institute of South Africa, incorporating the Liberty Life Chair of Exercise and Sports Science, the Medical Research Council and the University of Cape Town Bioenergetics of Exercise Research Unit, Department of Physiology, University of Cape Town Medical School
  • , Timothy D. NoakesAffiliated withSports Science Institute of South Africa, incorporating the Liberty Life Chair of Exercise and Sports Science, the Medical Research Council and the University of Cape Town Bioenergetics of Exercise Research Unit, Department of Physiology, University of Cape Town Medical School
  • , Steven C. DennisAffiliated withSports Science Institute of South Africa, incorporating the Liberty Life Chair of Exercise and Sports Science, the Medical Research Council and the University of Cape Town Bioenergetics of Exercise Research Unit, Department of Physiology, University of Cape Town Medical School

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Summary

This review suggests that there is little or no effect of elevating pre-exercise muscle glycogen contents above normal resting values on a single exhaustive bout of high-intensity exercise lasting less than 5 minutes. Nor is there any benefit of increasing starting muscle glycogen content on moderate-intensity running or cycling lasting 60 to 90 minutes. In such exercise substantial quantities of glycogen remain in the working muscles at the end of exercise. However, elevated starting muscle glycogen content will postpone fatigue by ≈20% in endurance events lasting more than 90 minutes. During this type of exercise, exhaustion usually coincides with critically low (25 mmol/kg wet weight) muscle glycogen contents, suggesting the supply of energy from glycogen utilisation cannot be replaced by an increased oxidation of blood glucose. Glycogen supercompensation may also improve endurance performance in which a set distance is covered as quickly as possible. In such exercise, high carbohydrate diets have been reported to improve performance by 2 to 3%.