 The investigators will determine the effects of exercising at two different intensities compared to a control non-exercise condition on neuroplastic potential in depressed and non-depressed subjects. To accomplish this aim, the investigators will have subjects ride a cycle ergometer at intensities set to elicit 35 low and 70 high of heart rate reserve 220 - age - resting heart rate x 35 or 70 resting heart rate. Prior to, and immediately after exercise participants will have their neuroplastic potential tested via transcranial magnetic stimulation TMS, blood specimens sampled, and mood changes assessed methods detailed below. These assessments will occur at these time points and then every 15 minutes for 1 hour after exercise. 