1. Physical Medicine and Rehabilitation Service, Hunter Holmes McGuire VA Medical Center, Richmond, VA 23249, USA
2. Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, VA 23284, USA
3. Department of Biology, Virginia Commonwealth University, Richmond, VA 23284, USA
4. Department of Nursing, Old Dominion University, Norfolk, VA 23529, USA
5. Department of Physical Medicine and Rehabilitation, Virginia Commonwealth University, Richmond, VA 23298, USA