Foad, A. J., Beedie, C. J., & Coleman, D. A. (2008). Pharmacological and psychological effects of caffeine ingestion in 40-km cycling performance. Medicine and Science in Sports and Exercise, 40, 158-165.

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This study explored the psychological and pharmacological effects of caffeine in laboratory cycling performance. Male competitive cyclists (N = 14) performed 14 40-km time trials (eight experimental trials interspersed with six baseline trials). The experimental phase consisted of two trials for each of four experimental conditions: informed caffeine/received caffeine, informed no treatment/received caffeine, informed caffeine/received placebo, and informed no treatment/received no treatment.

Relative to baseline, a very likely beneficial main effect of receiving caffeine and a possibly beneficial main effect of being informed of caffeine were observed. A substantial interaction between belief and pharmacology indicated that caffeine exerted a greater effect on performance when Ss were informed that they had not ingested it. Belief exerted a greater influence on performance in the absence of caffeine. A possibly harmful negative placebo effect was observed when Ss were correctly informed that they had ingested no caffeine. No clinically significant changes relative to baseline were observed in mean heart rate. Clear and substantial increases in blood lactate were evident after receipt of caffeine.

Implication. Expectations about performance influence performance positively depending upon the athlete's awareness of whether they have ingested caffeine prior to the performance. When Ss think they have not received caffeine, but actually have received it, performance is enhanced. However, when Ss believe they have not received caffeine and actually have not received it, performance is inferior. Thus, caffeine effects override beliefs. It is only when there is no caffeine ingested that beliefs modify performance.

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