The assessment and treatment of chronic pain (CP) and Posttraumatic Stress Disorder (PTSD) are national priorities for the National Institute of Health (NIH) and the Veterans Health Administration (VHA) as we continue to see steep increases in the prevalence of these conditions among returning Veterans as well as relatively high rates of these conditions among civilians. Health behavior change is important in treating these conditions and proactively preventing long-term negative health sequelae, in order to benefit these individuals directly and reduce the challenges to our healthcare system. We will use an innovative translational research approach to study whether a progressive -based exercise program will help individuals suffering from CP/PTSD achieve exercise maintenance, and shared symptom reduction, through neuropeptide Y mediated improvements in putative factors known to improve exercise related self-efficacy and motivation. This study will compare the effects of a 3-month, individually prescribed progressive exercise training program on: 1) chronic pain (CP), depression and PTSD symptoms, and 2) neurobiological and related neuropsychological mechanisms by which our exercise-training paradigm may foster exercise maintenance.