Objective:Brain-derived neurotrophic factor (BDNF) has recently emerged as one potential mechanism with which exercise improves mood in major depressive disorder (MDD). This study examined the relationship between changes in serum total BDNF and mood following acute exercise in MDD. It was hypothesized that acute exercise would increase BDNF in an intensity-dependent manner and that changes in BDNF would be significantly related to improvement in depressed mood post-exercise.

Methods: Twenty-four women (age: 38.6 ± 14.0 years) with MDD exercised for 30 min on a stationary bicycle at light, moderate and hard exercise intensities and performed a quiet rest session using a within-subjects, randomized and counter-balanced design. Before, 10 and 30 min after each session, participants completed the profile of mood states (POMS). Blood was drawn before and within 10 min after completion of each session and serum total BDNF (sBDNF) was measured by enzyme-linked immunosorbent assay. Acute exercise-induced changes in POMS Depression and sBDNF were analyzed via 4 session (quiet rest, light, moderate, hard) by 2 measurement (pre, post) ANOVA. Secondary analyses examined the effects of baseline mood and antidepressant usage on sBDNF.

Results: Exercise resulted in an acute improvement in depressed mood that was not intensity dependent (p > 0.05), resulting in significant acute increases in sBDNF (p = 0.006) that were also not intensity-dependent (p > 0.05). Acute changes in sBDNF were not significantly correlated to changes in POMS depression at 10 m (r = −0.171, p = 0.161) or 30 m (r = −0.151, p = 0.215) post-exercise. The fourteen participants taking antidepressant medications exhibited lower post-exercise sBDNF (p = 0.015) than the participants not currently taking antidepressants, although mood responses were similar.

Conclusion:Acute exercise is an effective mood-enhancing stimulus, although sBDNF does not appear to play a role in this short-term response. Patients who are not currently taking antidepressant medications and those who have greater pre-exercise depression may experience a greater sBDNF response to exercise, but the clinical significance of this is currently unclear. Circulating BDNF levels are unlikely to be altered by steady-state acute exercise in a linear dose-dependent manner. This does not eliminate its potential relevance in the antidepressant response to chronic exercise training, but suggests that other mechanisms are involved in the acute affective response to exercise in depression.