The Effect of Carbohydrate Beverage Ingestion on Central versus Peripheral Fatigue: A Placebo-Controlled, Randomized Trial in Cyclists.

OBJECTIVE

We investigated whether carbohydrate ingestion delays fatigue in endurance-trained cyclists via peripheral or central mechanisms.

METHODS

Ten men [35±9 yrs] and ten women [42±7 yrs] were assigned, in a double-blind, cross-over design to a sports drink [CHO] and placebo [PL]. Strength measures were made 3 times [pre-exercise, post-time trial and post-ride to exhaustion]: 1) Maximal voluntary contraction [MVC]; 2) MVC with superimposed femoral nerve magnetic stimulation to measure central activation ratio [CAR]; 3) femoral nerve stimulation in a 3-second pulse train on relaxed muscle. Subjects cycled 2 hours at ~65% of peak oxygen consumption [VO2peak], with 5 1-minute sprints interspersed, followed by a 3-km time trial. After strength testing, cyclists remounted their bikes, performed a brief warmup, and pedaled at ~85% VO2peak until unable to maintain workload. Changes in metabolic and strength measurements were analyzed with repeated measures ANOVA.

RESULTS

From pre-exercise to post-time trial: MVC declined in men (17%) and women (18%) [p=0.004] with no effect of beverage [p>0.193]; CAR decreased in both sexes with PL [P=0.009], the decline was attenuated by CHO in men only [time×treatment, p=0.022]; there was no evidence of peripheral fatigue in either sex with either beverage [p>0.122]. Men rode faster in the time trial with CHO [p=0.005] but did not improve performance in the ride to exhaustion [p=0.080]. In women, CHO did not improve performance in the time trial [p=0.173], or in the ride to exhaustion [p=0.930].

CONCLUSIONS

Carbohydrate ingestion preserved central activation and performance in men, but not women, during long-duration cycling.