Carbohydrate Intake of 100 vs. 60 g·h⁻¹ During Prolonged Cycling Improves Durability Without Altering Muscle Glycogen Utilization in Male Endurance Athletes

PURPOSE: To investigate the effects of ingesting 60 versus 100 g CHO·h⁻¹ during prolonged cycling on durability, substrate oxidation, and muscle glycogen utilization in endurance athletes. METHODS: Fifteen trained male cyclists and triathletes completed a 15-min time trial (15-min TT) in a fresh state and following two prolonged intermittent cycling (PIC) protocols. After consuming a CHO-enriched diet for 24 hours, participants cycled for 240 min at 60 % of their fresh 15-min TT mean power output (MPO₁₅min), interspersed with high-intensity intervals. In a randomized, double-blind, crossover design, participants consumed either 60 g CHO·h⁻¹ (CHO60) or 100 g CHO·h⁻¹ (CHO100) through beverages and gels in a 1:0.8 glucose:fructose ratio. Muscle biopsies were obtained from m. vastus lateralis before and after the PIC protocols to assess glycogen content. RESULTS: 15-min TT performance was impaired after the PIC protocol in both conditions but with a greater reduction in CHO60 compared with CHO100 (-9.3 ± -2.0% vs -6.4 ± -1.7%, P= 0.025). Accordingly, MPO₁₅ was 9 W higher in CHO100 than CHO60 (P = 0.028). Muscle glycogen content decreased substantially during exercise, with similar glycogen availability after the PIC protocols between conditions (CHO60: 192 ± 99 mmol · kg -1 DW; CHO100: 209 ± 111 mmol · kg -1 DW, P = 0.56). Whole-body CHO oxidation was better preserved during the PIC protocol in CHO100 (CHO60: 2.6 ± 0.6 g·min -1 to 1.9 ± 0.4 g·min -1, CHO100: 2.6 ± 0.4 g·min -1 to 2.3 ± 0.5 g·min -1, condition x time; P = 0.047), whereas blood glucose concentrations remained stable in both conditions (CHO60: 5.6 ± 1.0 mmol·L -1 to 5.7 ± 0.9 mmol·L -1, CHO100: 6.0 ± 0.9 mmol·L -1 to 6.1 ± 0.9 mmol·L -1, effect of time; P = 0.43). CONCLUSIONS: Consuming 100 versus 60 g CHO·h⁻¹ during prolonged intermittent cycling improved durability without altering muscle glycogen utilization.