Exploring the potential synergistic pharmacological and psychological effects of caffeine on exercise performance: a placebo-balanced study.

抄録

Research specifically investigating the distinct pharmacological and expectancy effects of caffeine using the deceptive placebo-balanced design remains scarce and with contradictory results. The aim of this study was to investigate the potential synergy between the pharmacological and expectancy effects of caffeine on exercise performance by using a placebo-balanced design. Sixteen physically trained athletes (11 males and 5 females; 21.7 ± 5.0 yr) participated in a study with a deceptive protocol including four randomized conditions: placebo informed-placebo ingested (control); placebo informed-caffeine ingested (pharmacological effect); caffeine informed-placebo ingested (expectancy effect); and caffeine informed-caffeine ingested (combined effects). Sixty minutes after ingestion, participants performed a countermovement jump, a standing triple jump, a medicine ball throw and a 20-m running sprint test. Relative to control, the pharmacological effect trial increased standing triple jump distance (+2.1% p = 0.032; Cohen's d= 0.59) and reduced 20-m sprint time (-0.8% p = 0.030; Cohen's d= 0.60). The combined effect trial reduced 20-m sprint time (-0.8% p = 0.021; Cohen's d= 0.64) in comparison to control. The expectancy effect trial did not modify performance in any of the performance tests with respect to control. When averaging the performance across all four tests, improvements relative to the control trial were +0.9%, +0.6% and +1.3% for pharmacological, expectancy and combined effects, respectively. The ingestion of caffeine, whether or not participants expected to receive it, improved exercise performance. This suggests that the primary driver of caffeine's ergogenic effect is its pharmacological action, with only a minor contribution from expectancy.