The psychological effects of physical exercise: A controlled study of the placebo effect

Abstract

The research on well-being and physical exercise point to the possibility of a placebo effect. This study analyzes the effect of expectancy manipulation on psychological (well-being and self-esteem) and physical (agility and cardiorespiratory fitness) outcomes after a seven-week program of aerobic training. 114 undergraduate students (age M = 19.81, SD = 1.75; 86.1% women) were randomized into G1 - No Exercise (n = 13), G2 - Exercise only (n = 15), G3 - Exercise + Manipulation of expectations: No psychological effect (n = 17) and G4 - Exercise + Manipulation of expectations: Psychological effect (n = 21). Outcome measures were the Rosenberg Self-Esteem Scale, the Well-Being subscale of the Subjective Exercise Experiences Scale, the Agility T-test and the 20-meter Shuttle Run Test. Paired t-tests showed significant improvements from baseline in self-esteem, agility, and cardiovascular fitness for the exercise groups. G4 also showed a significant improvement in well-being. ANCOVA with adjustments for the baseline measures was used to test between-group differences at the end of the program. The only significant differences at posttest were between G1 and the exercise groups. The data do not support a differential effect of elevated expectations of psychological benefits on the participants' self-esteem or psychological well-being after an aerobic training program. Future research should analyze whether reinforcing expectations more frequently throughout the program might show a more robust influence.

Keywords: Physical activity; expectations; placebo; self-esteem; well-being.