This trial will also determine the relative responsiveness (compared to traditional clinical scales) of the iMOBILITY for testing the hypothesis that intensive exercise can improve mobility in PD. We will use existing instruments (Berg Balance Scale, BEST of dynamic balance, UPDRS, PDQ-39, 5 times sit-to-stand time and the Functional Performance Battery) to show there is a difference between the exercise groups. Superior responsiveness of the iMOBILITY system will be determined by larger differences with exercise intervention with the iMOBILITY system than with traditional clinical measures of mobility in PD.