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Carbohydrate Attenuates Central Fatigue in Male and Female Cyclists

Beth W. Glace, MS, Ian J. Kremenic,MEng, Malachy P. McHugh, PhD, FACSM

Purpose:  Carbohydrate ingestion [C] delays fatigue during submaximal exercise.

The purpose of this study was to identify the mechanism [peripheral vs. central] by which carbohydrate ingestion delays fatigue after exhaustive cycling.

Methods:  10 men [35±2.9yrs; VO2peak 60.3±2.3 ml/Kg/min] and 5 women [43±1.6 yrs; 44.7±2.7ml/Kg/min] were assigned, in a double-blind  cross over design, to an artificially sweetened, non-caloric, electrolyte beverage [4C Totally Light 2 Go; “PL”] and to a commercially available sports drink [Gatorade; “CHO”] at a rate of 1% of body weight each hour.  Subjects cycled for 2 hours at their ventilatory threshold [64% of VO2peak] with 5, 1-minute sprints interspersed, followed by a 3-km time trial.   Intensity was then increased to the workload at their respiratory compensation threshold [84% VO2peak] and subjects were encouraged to pedal for as long as possible.  Ratings of perceived exertion [RPE] were measured throughout using a Borg scale. Blood glucose, lactate and quadriceps strength were measured pre-exercise, at one hour of cycling, post-3 km time trial and post-exhaustion.  Isometric strength testing was performed in a semi-reclined position: 1) MVC; 2) MVC with superimposed femoral nerve magnetic stimulation to measure central activation ratio [CAR]; 3) peripheral magnetic stimulation of the femoral nerve [PMS] in a 4-second pulse train on relaxed muscle. Changes in metabolic and strength measurements were analyzed with repeated measures ANOVA.

Results:  Following the 3k-time trial, voluntary strength declined by 16% in men [p=0.001] and 19% in women [p=0.015.]  Carbohydrate better maintained central activation in men [CHO CAR 94% of baseline vs. PL CAR 82% of baseline, p=0.022]. There was no evidence of peripheral fatigue, based on maintenance of PMS-elicited force, in either gender [time, p>0.1; time x drink, p>0.5.]  CHO improved time trial [p=0.005] performance in men, but not time to exhaustion [p=0.13], and improved neither performance in women [p>0.5].  Blood glucose was better maintained with CHO [effect of drink x time  p=0.02] but CHO had no effect on lactate.

Conclusion:  Carbohydrate ingestion preserves central activation during long duration cycling in men.

Author affiliations:

Nicholas Institute of Sports Medicine and Athletic Trauma, Lenox Hill Hospital, New York, NY.

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