Nonplacebo controls to determine the magnitude of ergogenic interventions: a systematic review and meta-analysis.

Marticorena, Felipe Miguel; Carvalho, Arthur; de Oliveira, Luana Farias; Dolan, Eimear; Gualano, Bruno; Swinton, Paul; Saunders, Bryan

Abstract

Introduction: Placebos are used as a control treatment that is meant to be indistinguishable from the active intervention. However, where substantive placebo effects may occur, studies that do not include a non-placebo control arm may underestimate the overall effect of the intervention (active plus placebo components). This study aimed to determine the relative magnitude of the placebo effect associated with nutritional supplements (caffeine and extracellular buffers) by meta-analysing data from studies containing both placebo and non-placebo control sessions. Methods: Bayesian multilevel meta-analysis models were used to estimate pooled effects and express the placebo effect as a percentage of the overall intervention effect. Results: Thirty-four studies were included, with the median pooled effect size (ES0.5) indicating a very small (ES0.5=0.09 [95%CrI:0.01 to 0.17]) improvement in performance of placebo compared to control. There was no moderating effect of exercise type (capacity or performance), exercise duration or training status. The comparison between active intervention and control indicated a small to medium effect (ES0.5=0.37 [95%CrI:0.20 to 0.56]). Expressed in relative terms, the placebo effect was equivalent to 25% [75%CrI:16 to 35%] and 59% [75%CrI:34 to 94%] of the total intervention effect for buffers and caffeine. Conclusion: These results demonstrate a very small, but potentially important placebo effect with nutritional supplementation studies. A substantive proportion of supplement effects may be due to placebo effects, with the relative proportion influenced by the magnitude of the overall ergogenic effect. Where feasible, intervention studies should employ non-placebo control-arm comparators to identify the proportion of the effect estimated to come from placebo effects and avoid underestimating the overall benefits that the physiological plus psychobiological aspects associated with an intervention provide in the real world.

Citation

MARTICORENA, F.M., CARVALHO, A., DE OLIVEIRA, L.F., DOLAN, E., GUALANO, B., SWINTON, P. and SAUNDERS, B. 2021. Nonplacebo controls to determine the magnitude of ergogenic interventions: a systematic review and meta-analysis. Medicine and science in sports and exercise [online], 53(8), pages 1766-1777. Available from: https://doi.org/10.1249/MSS.0000000000002635

• Journal Article Type: Review
• Acceptance Date: Feb 4, 2021
• Online Publication Date: Feb 12, 2021
• Publication Date: Aug 31, 2021
• Deposit Date: Feb 8, 2021
• Publicly Available Date: Feb 13, 2022
• Journal: Medicine and science in sports and exercise
• Print ISSN: 0195-9131
• Electronic ISSN: 1530-0315
• Publisher: Lippincott, Williams & Wilkins
• Peer Reviewed: Peer Reviewed
• Volume: 53
• Issue: 8
• Pages: 1766-1777
• DOI: https://doi.org/10.1249/MSS.0000000000002635
• Keywords: Exercise; Nutrition; Physiology; Belief; Expectation; Neurobiological
• Public URL: https://rgu-repository.worktribe.com/output/1187319