BackgroundPhysical exercise as adjunctive treatment for hospitalized patients with major depressive disorder (MDD) has been of increasing interest in the past few years. While preliminary findings are promising, these prior studies have been plagued by inclusion of participants at different stages of medication use at study entry. The present study evaluates the effects of a short (10-days) add-on endurance-training intervention in hospitalized MDD patients on antidepressant medication for less than two weeks. MethodThirty-five participants were randomly assigned to one of three study groups: aerobic exercise (n=14), placebo (stretching) exercise (n=11), or no intervention (control; n=10). The study outcome was the change in the Beck Depression Inventory (BDI-II) total score from baseline to the end of the study period. ResultsThe intent-to-treat analysis showed significant improvements in BDI-II scores for both the aerobic and the stretching groups. However, comparing pre- to post-study depression changes in these two groups, we found a large effect size in favor of aerobic exercise (Cohen's d=−1.06). No significant change in depressive symptoms was found in the control group. LimitationsThe nature of the intervention (i.e., exercise) meant blinding participants to treatments was not possible. Precise information on medication dosage was not available, and the short duration of interventions and lack of follow-up assessment were all limitations. ConclusionsEndurance-training can be a helpful adjunct treatment for hospitalized patients with severe affective disorders in the initial stages of pharmacotherapy.