Harger-Domitrovich, S. G., McClaughry, A. E., Gaskill, S. E., & Ruby, B. C. (2007). Exogenous carbohydrate spares muscle glycogen in men and women during 10 h of exercise. Medicine and Science in Sports and Exercise, 39, 2171-2179.

This study evaluated the effects of carbohydrate supplementation on whole-body and net muscle substrate use during 10 hours of discontinuous exercise (occupational simulations) in men (N = 7) and women (N = 6). Ss performed a graded exercise on a treadmill and cycle ergometer to determine ventilatory threshold and VO2peak. Ss received either carbohydrate [20% maltodextrin (0.6 g/kg)] or a flavored placebo drink each hour across 10 hours of exercise. Exercise intensity was ~71% of ventilatory threshold for treadmill running and ~72% of ventilatory threshold for cycle ergometry. Hourly exercise included nine minutes of upper-body ergometry, 19 minutes of cycling, and 20 minutes of treadmill walking, with a 1-minute transition between modes, followed by a 10-minute rest and feeding period. The protocol was selected to simulate arduous occupational settings.

Whole-body carbohydrate oxidation was maintained during the carbohydrate trial compared with the placebo trial. Net muscle glycogen use was 52% higher for the placebo trial than the carbohydrate trial. There were no significant gender-specific differences in glycogen use, whole-body substrate oxidation, or blood glucose values.

Implication. Carbohydrate ingestion during long-duration exercise decreases net muscle glycogen use while maintaining better whole-body carbohydrate oxidation, and potentially increasing performance in field settings.

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