Timing Carbohydrate Beverage Intake During Prolonged Moderate Intensity Exercise Does Not Affect Cycling Performance

Abstract

Carbohydrate beverages consumed during long-term exercise have been shown to attenuate fatigue and improve performance; however, the optimal timing of ingestion is unclear. Therefore, the purpose of this study was to determine if timing the carbohydrate ingestion (front-loading (FL), continual loading (CL), and end-loading (EL)) during prolonged exercise influenced exercise performance in competitive cyclists. Ten well-trained cyclists completed three separate exercise bouts on a bicycle ergometer, each lasting 2 hours at an intensity of ~67% VO2 max, followed by a 15-minute “all out” time trial. In the FL trial, participants ingested a carbohydrate beverage during the first hour and a placebo beverage during the second hour. In the CL trial, a carbohydrate beverage was ingested throughout the trial. In the EL trial, a carbohydrate beverage was ingested during the second hour and a placebo during the first hour. The amount of carbohydrate consumed (75 g) was the same among conditions. The order of conditions was single-blinded, counterbalanced, and determined randomly. Performance was measured by the work output during the 15-minute performance ride. There were no differences in work output among the three conditions during the final time trial. In the first hour of exercise, peak venous blood glucose was highest in the FL condition. In the second hour, peak venous blood glucose was highest in the EL condition. Following the time trial, venous blood glucose levels were similar among FL, CL, and EL. Overall, the timing of carbohydrate beverage consumption during prolonged moderate intensity cycling did not alter cycling performance.