Aerobic exercise or stretching as add-on to inpatient treatment of depression: Similar antidepressant effects on depressive symptoms and larger effects on working memory for aerobic exercise alone

Aerobic exercise (AE) has positive effects on symptom severity and cognitive symptoms of depression. Since data on AE as add-on to inpatient treatment in depression is still scarce, we conducted this double-blind randomized controlled study. Patients aged between 18 and 60 years were recruited into the study if Hamilton Depression Rating Scale 17 (HDRS-17) score was >16. Participants were randomly assigned to either AE or basic stretching activities (control), which took place 3x/week for 6 weeks. Primary outcome was depression severity as assessed with the HDRS-17 and the Beck Depression Inventory (BDI). Further physiological and psychological variables and cognitive performance were assessed as secondary outcomes. Forty-two patients were included in the analysis (exercise: n = 22; control: n = 20). Regardless of group allocation, we found a significant short-term time effect for symptom-severity (HDRS17: p<0.001, η²=0.70; BDI: p<0.001, η²=0.51), mental toughness (p<0.001, η²=0.32), physical self-description endurance score (p = 0.013, η²=0.16), cognitive flexibility (p = 0.013, η²=0.14), and body mass index (BMI) (p = 0.006, η²=0.19). Working memory showed a significant time by group interaction in favor of AE (p = 0.043, η²=0.10). Short-term effects on symptom severity, mental toughness and BMI remained stable across the 6-month follow-up period. Finally, self-reported physical activity increased significantly from baseline to follow-up (p = 0.014, η²=0.15). The sample-size is rather small. The control intervention might have been too active as to find a time by group interaction for symptom severity. AE was associated with comparably large depression alleviation vs. stretching and with add-on benefits on working memory.