1. VA RR&D Maryland Exercise and Robotics Center of Excellence, Baltimore, MD, USA
2. Department of Physical Therapy and Rehabilitation Science, University of Maryland School of Medicine, Baltimore, MD, USA
3. Department of Neurology, University of Maryland School of Medicine, Baltimore, MD, USA
4. University of Maryland Rehabilitation and Orthopedics Institute (UMROI), University of Maryland School of Medicine, Baltimore, MD, USA
5. Department of Bioengineering, University of Maryland School of Engineering, College Park, MD, USA
6. Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
7. Department of Medicine, University of Maryland School of Medicine, Baltimore, MD, USA
8. Geriatrics Research, Education and Clinical Center, Baltimore Veterans Affairs Medical Center, Baltimore, MD, USA