1. a Department of Biomedical Engineering, Virginia Commonwealth University, P. O. Box 843067, Richmond, VA 23284, USA; Physical Medicine & Rehabilitation Service, Hunter Holmes McGuire VA Medical Center, Richmond, VA 23249, USA
2. b Department of Biomedical Engineering, Virginia Commonwealth University, P. O. Box 843067, Richmond, VA 23284, USA
3. c Department of Biomedical Engineering, Virginia Commonwealth University, P. O. Box 843067, Richmond, VA 23284, USA
4. d Department of Anatomy and Neurobiology, Virginia Commonwealth University, Richmond, VA 23298, USA
5. e Department of Biomedical Engineering, Virginia Commonwealth University, P. O. Box 843067, Richmond, VA 23284, USA. glbowlin@vcu.edu