1. Tim and Caroline Reynolds Center for Spinal Stimulation, Kessler Foundation, West Orange, NJ 07052, USA
2. Department of Bioengineering, University of Louisville, Louisville, KY 40292, USA
3. Kentucky Spinal Cord Injury Research Center, University of Louisville, Louisville, KY 40202, USA
4. Division of Physical Medicine and Rehabilitation, University of Louisville, Louisville, KY 40292, USA
5. Department of Medicine, University of Udine, 33100 Udine, Italy