Efficacy of adjunctive exercise for the behavioral treatment of major depression
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Exercise alone is an efficacious intervention for depression, but few studies have identified the benefits of using exercise to augment other psychosocial treatments. The purpose of the current series of studies was to examine the feasibility, acceptability, efficacy, and potential mechanism of the augmentation of behavioral activation (BA) with exercise. The starting point for this series was a meta-analysis of the strength and reliability of brain-derived neurotrophic factor (BDNF) as a putative mechanism of the mood and cognitive effects of exercise. Evaluating 29 studies, I found: (1) a moderate effect for BDNF increases following acute exercise, (2) a moderate effect for the intensification of this effect following a program of exercise, and (3) a small effect on resting BDNF following a program of exercise. Given these effects, I hypothesized that exercise added to BA would improve mood beyond that for BA combined with a control condition and that changes in BDNF would mediate these effects. In a clinical trial, 32 sedentary, depressed patients received 9 sessions of BA over 12 weeks and were randomized to receive an exercise or control (stretching) augmentation. Assessments of depression, quality of life, distress intolerance, perceived stress, cognition (memory, attention), and amount of exercise were conducted across the treatment period. Results demonstrated strong credibility ratings and completion rates comparable to other exercise interventions. The randomized treatment failed to lead to differential exercise between groups; all participants exercised more over time. Similarly, participants, regardless of condition, significantly improved on all outcome measures over time. BDNF significantly increased following acute exercise. However, the amount of exercise completed over time was not significantly related to changes in BDNF across acute episodes, nor did resting BDNF significantly improve over time. Nonetheless, effect sizes for these changes were in the moderate range, reflecting values for the literature as a whole. Finally, contrary to my hypothesis, BDNF changes were not associated with subsequent improvement in depression symptoms. Results from this trial raise questions whether BA may be a powerful enough intervention to increase exercise, thus explicit exercise prescriptions may not be necessary for patients receiving this intervention.