Abstract
PURPOSE: The effects of carbohydrate intake on temporal changes in power output during cycling were examined. METHODS: Eight male cyclists (VO2max: 62 ± 6 mL[BULLET OPERATOR]kg-1[BULLET OPERATOR]min-1) completed two trials consisting of 120 min of constant load cycling at 55% Wmax, followed by a simulated 30 km time trial (TT). Subjects consumed 150 ml of a glucose-fructose solution (CHO) or a non-caloric placebo (PL) every 15 minutes during the constant-load portion of the trial, and at 7.5 km intervals during the TT. Average power output during the TT was compared between treatments, and changes in power output within trials were examined across four segments of the TT (S1 = 0-7.5 km, S2 = 7.5-15 km, S3 = 15-22.5 km, and S4 = 22.5-30 km). Power output was also averaged for three minutes immediately before and after each feeding, to determine if changes in pacing between treatments were influenced by the proximity to CHO feedings. Magnitude-based qualitative inferences were used to evaluate differences between treatments and/or time-points. RESULTS: Average TT power output during the CHO trial (242 ± 30 W) was ‘likely’ greater than PL (217 ± 40 W). In the PL trial, cycling power ‘almost certainly’ decreased between S1 (235 ± 41 W) and S2 (223 ± 38 W), and ‘likely’ decreased further during S3 (201 ± 41 W). Subsequently, cycling power ‘very likely’ increased between S3 and S4 (219 ± 43 W), but remained lower than S1 levels. By contrast, power output during the CHO trial showed no clear changes from S1 (246 ± 41 W) to S2 (242 ± 28 W). Thereafter, power output ‘possibly’ decreased during S3 (232 ± 27 W), followed by a ‘likely’ increase in power during S4 (249 ± 32 W), resulting in power levels during S4 that were similar to S1. Power output during the period immediately following each PL ingestion (210 ± 40 W) was not clearly different from the period prior to PL ingestion (213 ± 39 W); whereas power output immediately following CHO ingestion (244 ± 27 W) was ‘possibly’ increased versus pre-ingestion (236 ± 31 W). CONCLUSIONS: CHO ingestion increased average power output during a cycling TT and attenuated declines in power output over the duration of the trial, compared to PL. In addition, improvements in power output with CHO were possibly greater in the periods immediately following each feeding, potentially due to effects of CHO on the central nervous system.
Published Version
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