CARBOHYDRATE ACTS CENTRALLY WHEN PRESERVING CYCLING PERFORMANCE
Glace, B. W., Kremenic, I. J., & McHugh, M. P. (2012). Carbohydrate attenuates central fatigue in cyclists. Presentation 2346 at the 59th Annual Meeting of the American College of Sports Medicine, San Francisco, California; May 29-June 2, 2012.
This study attempted to identify the mechanism [peripheral or central] by which carbohydrate ingestion delays fatigue after exhaustive cycling. Ss (N = 4) were assigned, in a double-blind crossover design, to an artificially sweetened, non-caloric, electrolyte beverage (placebo)] and to a commercially available sports drink (Carbohydrate, Gatorade) at a rate of 1% of body weight each hour. Ss cycled for two hours at their ventilatory threshold (approximately 66% of VO2peak) with five 1-minute sprints interspersed, followed by a 3-Km time-trial. Intensity was then increased to the workload at their respiratory compensation threshold [approximately 85% VO2peak] and Ss were encouraged to pedal for as long as possible. Ratings of perceived exertion were measured throughout using the Borg scale. Blood glucose, lactate, and quadriceps strength were measured pre-exercise, post-3K time-trial, and post-exhaustion. Isometric strength testing was performed in a semi-reclined position: 1) for maximum voluntary contraction; 2) maximum voluntary contraction with superimposed femoral nerve magnetic stimulation to measure central activation ratio (the measure of central activity); and 3) femoral nerve stimulation in a 4-second pulse train on a relaxed muscle (the measure of peripheral activity).
Post-exercise strength was 92% of baseline in the carbohydrate trial vs. 75% in the placebo trial. Preservation of strength with carbohydrate was due to better maintenance of central activation ( 91% of baseline after carbohydrate ingestion vs. placebo at 80% of baseline). There was no evidence of peripheral fatigue based on maintenance of femoral nerve stimulation-elicited force. Carbohydrate intake tended to improve time-trial and ride-to-exhaustion performance. There was no effect of drink on blood glucose or lactate.
Implication. Carbohydrate ingestion preserves performance via a central mechanism during exhaustive cycling.
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