Predictors of Depression Treatment Response to Exercise

50 subjects with Major Depressive Disorder who are not currently receiving treatment will be enrolled in a 12-week exercise program, supervised by a trained exercise interventionist. Blood samples will be collected at baseline for analysis of inflammatory cytokines, as well as other potential biological predictors of treatment outcomes (i.e., BDNF). Assessments will gather data on potential clinical predictors of treatment outcomes (anxiety, stress, sleep). Assessments and sample collection will also occur at 3 time points during the treatment period (Weeks 4, 8, and 12) to identify mediators and correlates of treatment effects.