Effects of Adjunctive Exercise Therapy in Patients with Bipolar Depression: A Pilot Multicenter Cluster-Randomized Controlled Trial

Background/Objectives: Bipolar depression impairs psychosocial functioning, cognition, and quality of life. Evidence regarding adjunctive exercise remains limited. This pilot study evaluated the clinical and biological effects of adjunctive exercise in patients with bipolar depression. Methods: In this multicenter cluster-randomized controlled trial, 26 hospitalized patients were assigned by facility to treatment as usual plus supervised exercise (TAU + Ex) or supervised stretching (TAU + SC) for 6 weeks. Twenty-four completed the study (TAU + Ex, n = 14; TAU + SC, n = 10). Clinical outcomes and plasma tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6, IL-1β, IL-2, brain-derived neurotrophic factor (BDNF), and vascular endothelial growth factor-A (VEGF-A) were assessed at baseline and week 6. The trial was registered with the University Hospital Medical Information Network Clinical Trials Registry (UMIN-CTR; UMIN000045877; registered on 1 December 2021). Results: FAST and QIDS-SR scores improved significantly in both the exercise and stretching groups after the 6-week intervention, but no significant group × time interactions were observed. No significant group, time, or group × time effects were observed for any plasma biomarker. Before correction for multiple comparisons, nominal correlations were observed between changes in IL-1β and FAST, BDNF and FAST, and VEGF-A and Spotter performance. None remained statistically significant after Benjamini–Hochberg FDR correction. Conclusions: Adjunctive exercise therapy was not superior to active stretching. The exploratory biomarker–outcome correlations did not remain significant after correction for multiple comparisons and should be considered hypothesis-generating. Larger, adequately powered randomized controlled trials are warranted.