Pharmacological and psychological effects of caffeine ingestion in 40-km cycling performance

Aim: To explore the psychological and pharmacological effects of caffeine in laboratory cycling performance. Method: Fourteen male competitive cyclists performed 14 40-km time trials (eight experimental interspersed with six baseline). 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. Conditions were nonrandomized. ANOVA was used to estimate main effects and interactions for mean values of power, heart rate, blood lactate, and maximal oxygen uptake. Probabilistic inferences for mean power were based on a smallest worthwhile change of 1.5%. Results: Relative to baseline, a very likely beneficial main effect of receiving caffeine (3.5%; 95% confidence interval 1.5 to 5.5%), and a possibly beneficial main effect of being informed of caffeine (0.7%; -0.7 to 2.1%) were observed. A substantial interaction between belief and pharmacology indicated that caffeine exerted effect on performance in conditions when subjects were informed that they had not ingested it, whereas belief exerted a greater influence on performance in the absence of caffeine (2.6%; -0.7 to 5.9%). A possibly harmful negative placebo (nocebo) effect was observed when subjects were correctly informed that they had ingested no caffeine (- 1.9%; -4.1 to 0.3%). 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. Data for mean oxygen uptake were unclear. Conclusion: Our data support the ergogenic efficacy of caffeine but suggest that both positive and negative expectations impact performance.