Placebo effects in psychological outcomes of exercise
Lindheimer, Jacob Benjamin
MetadataShow full item record
This dissertation quantified the population placebo effect in psychological outcomes of exercise training and examined the role of expectations as a mechanism for post-exercise improvements in mood and cognition after acute cycling exercise. In a systematic review and meta-analysis of 9 eligible studies, 52 and 41 effects were used to calculate mean effect sizes for placebo-control and exercise-control comparisons. The placebo effect [Δ = 0.20 (95% CI -0.02, 0.41)] was found to account for over half of the true effect of exercise on psychological outcomes [Δ = 0.37 (95% CI 0.11, 0.63)]. Placebo effects were larger for (i) subjective compared to objective outcomes and (ii) low intensity exercise placebos compared to other placebo types. An experiment was conducted to measure placebo effects in a single bout of acute exercise. A balanced placebo design was used to compare the psychological effects of light intensity active and passive (placebo) cycling in the presence and absence of information designed to lead participants to expect a decrease in anxiety and an increase in feelings of energy and performance on a working memory task. Demand characteristics were attenuated by blinding participants to the purpose of the study and test administrators to the information condition assignment. Statistically significant main between-group effects for cycling condition (active, passive) and information (information, no information) were not found before or after statistical adjustments for hypothesized effect size moderators. The results suggest that (i) the placebo effect accounts for over half of the observed effect of exercise training on psychological outcomes, (ii) a single exposure to information about the anxiolytic, energy and memory benefits of acute exercise is inadequate for changing expectations about those benefits and subsequent responses to acute active or passive cycling, and (iii) passive cycling appears to be a useful comparison group in experiments examining the psychological consequences of acute exercise, especially those seeking to minimize placebo responses.