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

Introduction: We examined the placebo effect of caffeine and the combined effect of caffeine and caffeine expectancy on maximal voluntary strength. Methods: Fourteen men completed 4 randomized single-blind experimental trials: 1) Told caffeine, given caffeine (5mg.kg) (CC); 2) Told caffeine, given placebo (CP); 3) Told placebo, given placebo (PP); 4) Told placebo, given caffeine (PC). Maximal voluntary concentric force and fatigue resistance of the knee flexors and extensors was measured using isokinetic dynamometry. Results: 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. Conclusion: Caffeine caused an improvement in some aspects of muscle strength, however there was no additional effect of expectancy. Performance was poorer in participants who believed caffeine would have the largest benefit, which highlights a link between expected ergogenicity, motivation, and personality characteristics. Publisher statement: This is the peer reviewed version of the following article: Tallis, J. , Muhammad, B. , Islam, M. and Duncan, M.J. (2016) Placebo effects of caffeine on maximal voluntary concentric force of the knee flexors & extensors. Muscle & Nerve, volume 54 (3): 479-486, which has been published in final form at http://dx.doi.org/10.1002/mus.25060 This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.