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No Effect of Carbohydrate Ingestion on Fatigue During Long-Duration Cycling in Women

Beth W. Glace, Ian J. Kremenic, Malachy P. McHugh, FACSM. NISMAT Lenox Hill Hospital, New York, NY. (Sponsor: Malachy McHugh, FACSM)

PURPOSE: We have previously shown, in men, that carbohydrate ingestion during prolonged cycling attenuates central fatigue. The purpose of this study was to investigate the mechanisms of fatigue during cycling in women.

METHODS: 9 women [41.6±2.4 yrs; VO 2peak 46.5± 2.7 ml/Kg/min] were assigned, in a double-blind crossover 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 [62% 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 [83% 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% [p=0.002] and was not affected by beverage [p=0.19]. Further changes in strength were not seen at exhaustion. There were no differences between treatments in the decrements in CAR with CHO vs. PL [16% vs 15% loss, drink x time p=0.93]. There was also no evidence of peripheral fatigue, as PMS-elicited force tended to increase slightly after the time trial [time, p=0.08] and was not affected by beverage [p=0.94]. At exhaustion, PMS-elicited force returned to baseline in both conditions [p=0.5]. CHO affected neither time trial [p=0.17] nor ride to exhaustion performance [p=0.93]. Blood glucose was higher with CHO [effect of drink, p=0.002] and respiratory exchange ratio remained higher [time x drink, p<0.001] but CHO had no effect on lactate [p=0.38] or RPE [p=0.32].

CONCLUSION: Although we have previously found that carbohydrate ingestion preserved central activation and performance in men during long duration cycling, we did not find these effects in women.

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