Advancing the understanding of placebo effects in psychological outcomes of exercise: Lessons learned and future directions

Abstract

Despite the apparent strength of scientific evidence suggesting that psychological benefits result from both acute and chronic exercise, concerns remain regarding the extent to which these benefits are explained by placebo effects. Addressing these concerns is methodologically and at times conceptually challenging. However, developments in the conceptualisation and study of placebo effects from the fields of psychology, neuroscience, pharmacology, and human performance offer guidance for advancing the understanding of placebo effects in psychological responses to exercise. In clinical trials, expectations can be measured and experimentally manipulated to better understand the influence of placebo effects on treatment responses. Further, compelling evidence has shown that the contribution of placebo effects and their underlying neurobiological mechanisms to treatment effects can be measured without administering a traditional placebo (e.g. inert substance) by leveraging psychological factors such as expectations and conditioning. Hence, the purpose of this focused review is to integrate lessons such as these with the current body of literature on placebo effects in psychological responses to exercise and provide recommendations for future research directions.

Keywords: Behaviour; cognition; health; methodology; neuroscience.

Figure 1.

Distinguishing treatment effects from placebo effects and non-specific effects requires the inclusion of a placebo and no-treatment control group. Panel A shows the observed effect of exercise, which is estimated by comparing the change in the exercise group to the control group. Panel B shows the placebo effect, which is estimated by comparing the change in the placebo group to the control group. Panel C shows that the true effect of exercise can be estimated by subtracting the placebo effect from the observed effect of exercise. In a meta-analysis of nine randomised controlled studies that included an exercise, placebo, and control group, approximately half of the observed effect of exercise on psychological outcomes was attributed to placebo effects (Lindheimer et al., 2015).