Acute Effects of Resistance Exercise Volume on Physiological and Psychological Outcomes in Adults Diagnosed with Major Depressive Disorder: A Randomized Crossover Study

Background and Objectives: The aim of this study was to investigate the acute effects of resistance exercise volume on physiological and psychological outcomes in adults with Major Depressive Disorder (MDD). Methods: This randomized crossover trial included adults aged 18–59 years with MDD. Participants completed two resistance exercise conditions: high-volume resistance exercise (HV-RE; four sets of 10–12 RM) and low-volume resistance exercise (LV-RE; two sets of 10–12 RM). Both protocols consisted of 10 full-body exercises, with 60 s rest between sets and 90 s between exercises. Total training volume was calculated as sets x repetitions x load (kg). Blood lactate concentration was assessed at rest and 3 min post-exercise. Affective responses were measured using the Feeling Scale (FS), training self-efficacy using the Perceived Exercise Self-Efficacy Scale (PESE), and mood states using the Brunel Mood Scale (BRUMS). Results: Twenty-four participants [20 women (83.3%)] were included. Training volume (3944.8 ± 1471.5 vs. 7603.9 ± 2800.2 kg, p < 0.001, d = 1.64) and RPE (6.2 ± 1.3 vs. 8.2 ± 1.3, p < 0.001, d = 1.54) were lower in LV-RE than in HV-RE. Both conditions increased blood lactate concentration (p < 0.001, η2 = 0.77), with no between-condition differences (p = 0.184). Significant main effects of time were observed for total mood state (p < 0.001, η2 = 0.54), depression (p = 0.025, η2 = 0.20), anger (p < 0.001, η2 = 0.47), vigor (p < 0.001, η2 = 0.53), and fatigue (p = 0.037, η2 = 0.18), whereas tension and confusion did not change significantly (p > 0.05). A significant improvement in affective responses was also observed (p < 0.001, η2 = 0.44), with no significant condition × time interactions (p > 0.05). There were no significant changes in self-efficacy. Conclusions: Both resistance exercise protocols were associated with acute changes in mood states and improved affective responses, alongside increased blood lactate concentrations, with no statistically significant differences in these changes detected between conditions. LV-RE elicited lower perceived exertion than HV-RE, suggesting that lower-volume resistance exercise may be a less demanding option for adults with MDD.