Stimulus Expectancy and Stimulus Response of Caffeine on 4-km Running Performance: A Randomized, Double-blind, Placebo-controlled and Crossover Study.

The placebo effect of caffeine has been poorly investigated in endurance exercise. Therefore, the aim of this study was to analyze the placebo effect of caffeine on 4 km running performance in amateur runners. Twenty-two healthy and recreational male runners (25.5 ± 8.4 yrs; 75.0 ± 7.1 kg; 173.7 ± 6.3 cm) underwent a deceptive experimental design consisting of three different sessions: a) control (CON) in which participants did not ingest any substance; b) placebo (PLA) in which participants ingested a capsule filled with maltodextrin but they were informed that they would receive caffeine; c) caffeine (CAF) in which participants were informed that they would receive caffeine and actually received caffeine. After 60 min for substances absorption, participants performed a 4-km test and they completed the distance as fast as possible. The time employed to cover the distance was lower in PLA (17.4 ± 1.5 min) and CAF (17.4 ± 1.4 min) than CON sessions (18.6 ± 2.8 min; P<0.05). There were no differences in the 4-km times between PLA and CAF (P>0.05) and no differences were reported between treatments for RPE (P>0.05). In conclusion, there was a placebo effect of caffeine on a 4-km maximal running trial which entailed that believing to have ingested caffeine improved performance to a similar extent than actually receiving caffeine. Therefore, the expectancy induced by caffeine may be one of the mechanisms behinds the ergogenic effect of this stimulant on endurance exercise.