The Effects of Carbohydrate Loading on Muscle Glycogen Content and Cycling Performance

This study compared the effects of supplementing the normal diets of 8 endurance-trained cyclists with additional carbohydrate (CHO), in the form of potato starch, for 3 days on muscle glycogen utilization and performance during a 3-hr cycle ride. On two occasions prior to the trial, the subjects ingested in random order either their normal CHO intake of 6.15 +/- 0.23 g/kg body mass/day or a high-CHO diet of 10.52 +/- 0.57 g/kg body mass/day. The trial consisted of 2 hr of cycling at approximately 75% of VO2peak with five 60-s sprints at 100% VO2peak at 20-min intervals, followed by a 60-min performance ride. Increasing CHO intake by 72 +/- 9% for 3 days prior to the trial elevated preexercise muscle glycogen contents, improved power output, and extended the distance covered in 1 hr. Muscle glycogen contents were similar at the end of the 3-hr trial, indicating a greater utilization of glycogen when subjects were CHO loaded, which may have been responsible for their improved cycling performance.