Gyorkos, A. M., Michael, T. J., Cheatham, C. C., & Ricard, M. D. (2006). The effect of glycemic index and timing of meal on exercise to fatigue. Medicine and Science in Sports and Exercise, 38(5), Supplement abstract 1401.

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This study investigated the influence of carbohydrate (low and high glycemic index) feedings and timing of meal before exercise to fatigue. Ss (N = 5) performed a peak bike test and four experimental trials, separated by seven days. Upon arrival, Ss ingested 1 gm/kgBW of carbohydrates of a high glycemic index meal (H) or a low glycemic index meal (L) before exercise to fatigue. Ss waited 30 or 60 minutes following each test meal, totaling four experimental conditions (H30, L30, H60, L60). These conditions were completed in a counterbalanced fashion. The exercise regimen was consistent following each meal; 90 minutes cycling at 70% peak oxygen consumption (VO2peak) followed by an all-out sprint until fatigue. The subjects, for the 60-minute trial, had blood draws taken at -30, 0, +10, +30, +60, +90 minutes, and fatigue. One less blood sample was taken from the subjects waiting 30 minutes (0, +10, +30, +60, +90-min, and fatigue). Heart rate was taken at rest, every 10 minutes of exercise, and at fatigue. VO2 and respiratory exchange ratio measurements were taken for the first 30 minutes of exercise and at 10 minutes surrounding each blood draw.

No significant statistical differences were found for any of the variables between trials (H30, L30, H60, L60) including blood glucose, blood lactate, RPE, RER, VO2, and performance time.

Implication. The timing and glycemic index of meals did not influence time to fatigue. In addition, blood glucose levels remained essentially the same between conditions.

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