Do Motivational Placebo Cues Influence Resistance Training Adaptations?

The placebo effect is a psychobiological response capable of influencing physical performance. Although its impact in sports settings is well documented, few studies have investigated whether a placebo effect exists for resistance training (RT)-induced muscle strength and mass changes. This study examined whether strategies involving external motivational feedback can affect the effectiveness of RT potentiating muscle strength and lean mass gains in untrained individuals. Thirty-one volunteers (25.9 ± 4.4 years, 13 women) were assigned to either a PLACEBO group (with external motivational feedback strategies) or a N-PLACEBO group (no external motivational feedback strategies). Both groups followed the same 14-week RT protocol, but with individual load progression. Muscle strength was assessed via one-repetition maximum (1 RM), and changes in lean mass of the thigh and hip via dual-energy x-ray absorptiometry (DEXA), before (pre) and after (post) RT. A two-way repeated measures ANOVA showed significant pre-to-post increases in 1 RM and lean mass in both groups (main effect of time, p < 0.001), but no significant group-by-time interaction for muscle strength or lean mass (p > 0.05). We conclude that external motivational feedback strategies did not yield additional gains in muscle strength or lean mass of the thigh and hip in untrained individuals. Therefore, no placebo effect was observed for the analyzed outcomes.