This randomized pilot study will be conducted in men with metastatic castration resistant prostate cancer (mCRPC) within 3 months of initiating abiraterone or enzalutamide. The purpose of this pilot study is to evaluate the effects of a 12 week exercise intervention in mCRPC patients who have recently started on additional androgen suppression therapy. The investigators will also explore the effects of the exercise training on biomarkers of inflammation-hormonal status and their potential association with changes in lean mass and function.