Szuhany KL, et al. - Given the implication of brain-derived neurotrophic factor (BDNF) in depression and the findings from recent meta-analysis describing reliable effects of exercise on BDNF levels, researchers here investigated if in depressed patients, increased exercise was associated with enhanced BDNF response, and whether this change mediated clinical benefits. They randomized 29 depressed, sedentary participants to receive either behavioral activation plus an exercise or stretching prescription. They performed an assessment of blood samples collected prior to (resting BDNF levels) and following an exercise test (pre-to postexercise BDNF change) at four points and identified a significant increase in BDNF across all assessment points. During an exercise program, no intensification of BDNF changes across acute exercise was observed. No change in resting BDNF levels was observed across an exercise program. Further, no association of BDNF changes with changes in depression symptoms was evident.