The effect of caffeine ingestion on metabolism and performance during prolonged cycling
The purpose of this study was to investigate the effect of caffeine supplementation on physiological and performance parameters during 4-h of prolonged steady state cycling followed by a maximal performance time trial. Utilizing a randomized, double blind, crossover design, 11 trained endurance athletes cycled-for 4-h at ∼55% of maximal oxygen consumption (VO 2max ), 3-h after ingestion of 6 mg of caffeine-kg-1 or placebo. Subjects were also given a small carbohydrate meal 2-h prior to the 4h ride, an additional 3 mg of caffeine-kg-1 or placebo 1-h into the ride, and 1-L-h-1 of a 6% carbohydrate/electrolyte solution. Immediately after completion of the 4-h steady-state ride a maximal performance 5-km time trial was carried out. Seven days prior to each experimental trial, participants were instructed to abstain from caffeine containing products of any kind. During the 3-d preceding their first experimental trial, subjects were asked to maintain a high carbohydrate, pre-competition diet and record their food intake using a standard dietary record protocol. Subjects were also asked to record their physical activity during the 3-d preceding each experimental trial, and abstain from any exercise during the 24-h prior to their trial. Caffeine ingestion resulted in significantly elevated [FFA] at only 60-min after ingestion. This is the first study to investigate a regimen of multiple doses of caffeine in combination with carbohydrate intake during a long duration exercise bout. Given that this regimen was not associated with changes in steady state [FFA], [lactate], [glucose], RPE, respiratory or 5 km time trial performance it was concluded that caffeine intake when followed by carbohydrate ingestion, before and during exercise, does not alter indices of substrate utilization or benefit exercise performance in trained cyclists.