Placebo effects of caffeine on maximal voluntary concentric force of the knee flexors and extensors

We examined the placebo effect of caffeine and the combined effect of caffeine and caffeine expectancy on maximal voluntary strength.

Fourteen men completed 4 randomized, single-blind experimental trials: (1) told caffeine, given caffeine (5 mg/kg) (CC); (2) told caffeine, given placebo (CP); (3) told placebo, given placebo (PP); and (4) told placebo, given caffeine (PC). Maximal voluntary concentric force and fatigue resistance of the knee flexors and extensors were measured using isokinetic dynamometry.

A significant and equal improvement in peak concentric force was found in the CC and PC trials. Despite participants believing caffeine would evoke a performance benefit, there was no effect of CP.

Caffeine caused an improvement in some aspects of muscle strength, but there was no additional effect of expectancy. Performance was poorer in participants who believed caffeine would have the greatest benefit, which highlights a link between expected ergogenicity, motivation, and personality characteristics. Muscle Nerve 54: 479-486, 2016.