Heesch, M., Mieras, M., & Slivka, D. (2013). The performance effect of early versus late carbohydrate feedings during prolonged exercise. Medicine & Science in Sports & Exercise, 45(5), Supplement abstract number 575.

This study determined how the timing of isoenergetic carbohydrate feedings during prolonged cycling affects performance in a subsequent 10-km cycling time-trial in recreationally trained male cyclists (N = 8). Ss completed four experimental trials consisting of cycling continuously for two hours at 60% of VO2peak, followed immediately by a self-paced 10-km time-trial. Ss received 250 mL of beverage every 15 minutes during the two-hour exercise. The four conditions included no carbohydrate ingestion, early carbohydrate ingestion, late carbohydrate ingestion, or carbohydrate ingestion throughout. Trials were completed in a randomized, counterbalanced order. All trials in which carbohydrate was ingested were isoenergetic. Blood samples were obtained at 0, 60, and 120 minutes of cycling as well as at the conclusion of the time-trial.

10-km time-trial time to completion was faster in the carbohydrate ingestion throughout and late carbohydrate ingestion when compared to the no-ingestion control trial. The control and early ingestion trials were not different. After 60 minutes of cycling, serum glucose concentrations were higher in the ingestion throughout trial and early ingestion trial when compared to the other two conditions. After 120 minutes of cycling, serum glucose concentrations were higher in the ingestion throughout and late ingestion trials when compared to the other two conditions.

Implication. Carbohydrate ingestion late and throughout exercise can improve subsequent 10-km time-trial performance while early ingestion does not.

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