The effect of placebo-induced changes in expectancies on maximal force production in college students

This study used false information about a placebo (milk-sugar tablet) to induce expectancies regarding force production. Forty-two college students were assigned to a placebo/placebo (PP), placebo/no-placebo (PN), or control group, and underwent baseline testing and two trials assessing one-repetition maximum (1 RM) strength on a bench press and seated leg press. The PP and PN groups improved significantly compared to the control at Trial I for the bench press (p <=.01) and leg press (p <=.01). Disclosure of the true nature of the placebo resulted in force production declines in the PN group to levels approximating controls on the bench press (p >.05) and seated leg press (p >.05). The results suggest that placebo-associated expectancy effects played a significant part in the observed changes. Implications include information for coaches, teachers, and fitness enthusiasts about the importance of psychological factors in successful performance.