Outcome expectancy could mediate the psychological effects of exercise-related interventions, which implies that part of the psychological benefits of physical activity could be ascribed to placebo effects. In this framed field-experiment, 89 healthy participants were studied in three groups, (1) breathing-primed (deep-breathing with an exercise-related expectancy), (2) breathing-unprimed (deep-breathing with no exercise-related expectancy), and (3) control (no intervention). Deep-breathing lasted for three minutes. Before and after deep-breathing, or sitting quietly in the control group, participants completed two questionnaires assessing their positive- and negative affect (NA) and subjective well-being (WB). In contrast to the control group, both the breathing-primed and breathing-unprimed groups showed decreased NA and increased subjective WB. The breathing-primed group reported larger changes in WB than the breathing-unprimed group, in addition to also exhibiting significant increases in positive affect. These findings support the hypothesis of the work that expectations mediate the psychological effects of deep-breathing beyond the intervention's specific effects. Therefore, future research should control for expectations related to an intervention when gauging psychological changes.
Keywords: Anticipation; conditioning; exercise; mood; placebo.