Carbohyrate Ingestion Immediately Before Exercise Does Not Improve 20 km Time Trial Performance in Well Trained Cyclists

This study examined the effects of carbohydrate ingestion on 20 km cycle time-trial (TT) performance in 14 well-trained cyclists (11 males, 3 females; peak oxygen uptake [VO₂peak] 4.52 ± 0.60 l/min; values are mean ± SD). All subjects performed two experimental trials on their own bicycles mounted on an air-braked ergometry system (Kingcycle™). Subjects were instructed to maintain the same training and dietary regimens before trials, which were conducted in a random order, 3 - 7 days apart, and at the same time of day for each subject. On the day of a trial, subjects reported to the laboratory and ingested an 8 ml/ kg body mass bolus of either a 6.8 g/100 ml commercial carbohydrate-electrolyte (CHO) beverage (39 ± 4 g of CHO), or a coloured, flavoured placebo. Ten min after finishing the drink, subjects commenced a 5 min warm-up at 150 W, before commencing the 20 km TT. The average power output (312 ± 40 vs 311 ± 38W) and heart-rate (171 ± 6 vs 171 ± 5 beats/min for CHO and placebo, respectively) during the two rides did not differ between treatments. Accordingly, the performance times for the two TT's were the same (27:41 ± 1:39 min:sec, for both CHO and placebo). We conclude that the ingestion of ~ 40 g of carbohydrate does not improve maximal cycling performance lasting - 30 min, and that carbohydrate availability, in the form of circulating blood glucose, does not limit high-intensity exercise of this duration.

Key words

Cycling - endurance - fluid ingestion