1. Swiss Paraplegic Research, Nottwil, Switzerland
2. Department of Health Sciences and Health Policy, University of Lucerne, Lucerne, Switzerland
3. Department of Veterans Affairs, Human Engineering Research Laboratories, VA Pittsburgh Healthcare System, Pittsburgh, Pennsylvania, USA
4. Department of Rehabilitation Science and Technology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
5. Department of Physical Medicine and Rehabilitation, University of Pittsburgh, Pittsburgh, Pennsylvania, USA