This project will relate our new quantification of Freezing of Gait (FoG) in Parkinson's disease, using body worn inertial sensors (Aim I), with abnormalities in state-of-the-art, resting state, functional brain connectivity (Aim II), and determine the number of subjects needed for a future, randomized clinical trial to test the efficacy of our novel, Agility Boot Camp (ABC) rehabilitation intervention for FoG (Aim III). The technological approaches to these aims are cutting edge and will allow us to develop sensitive behavioral and brain biomarkers for gait disorders in Parkinson's disease (PD) for use in future clinical trials.