Is the effect of aerobic exercise on cognition a placebo effect?

Abstract

A number of studies and meta-analyses conclude that aerobic fitness (walking) interventions improve cognition. Such interventions typically compare improvements from these interventions to an active control group in which participants engage in non-aerobic activities (typically stretching and toning) for an equivalent amount of time. However, in the absence of a double-blind design, the presence of an active control group does not necessarily control for placebo effects; participants might expect different amounts of improvement for the treatment and control interventions. We conducted a large survey to explore whether people expect greater cognitive benefits from an aerobic exercise intervention compared to a control intervention. If participants expect greater improvement following aerobic exercise, then the benefits of such interventions might be due in part to a placebo effect. In general, expectations did not differ between aerobic and non-aerobic interventions. If anything, some of the results suggest the opposite (e.g., respondents expected the control, non-aerobic intervention to yield bigger memory gains). These results provide the first evidence that cognitive improvements following aerobic fitness training are not due to differential expectations.

Figure 1. Percentage of participants expecting improvement as a function of intervention group and task for all participants.

Percentage of participants within each intervention group who believed that completion of the intervention presented to them would improve task performance. Includes both sedentary and non-sedentary participants.

Figure 2. Believed improvement amount as a function of intervention group and task type for all participants.

Mean amount of improvement participants believed completion of the intervention presented to them would create. Includes both sedentary and non-sedentary participants. Error bars represent 95% confidence intervals.

Figure 3. Percentage of participants expecting improvement as a function of intervention group and task for sedentary participants.

Percentage of participants within each intervention group who believed that completion of the intervention presented to them would improve task performance. Includes only sedentary participants.

Figure 4. Believed improvement amount as a function of intervention group and task type for all participants.

Mean amount of improvement participants believed completion of the intervention presented to them would create. Includes only sedentary participants. Error bars represent 95% confidence intervals.