1. Human Engineering Research Laboratories, VA Pittsburgh Healthcare System, Pittsburgh, PA 15206, USA
2. Department of Rehabilitation Science and Technology, University of Pittsburgh, Pittsburgh, PA 15260, USA
3. Department of Kinesiology and Community Health, University of Illinois at Urbana-Champaign, Champaign, IL 61820, USA
4. Amsterdam Rehabilitation Research Center, Reade, 1040 HG Amsterdam, The Netherlands
5. University of Groningen, University Medical Center Groningen, Center for Human Movement Sciences, 9700 AB Groningen, The Netherlands
6. Rehabilitation Engineering Research Program, Minneapolis VA Healthcare System, Minneapolis, MN 55417, USA
7. Department of Physical Medicine and Rehabilitation, Program in Rehabilitation Science, University of Minnesota, Minneapolis, MN 55455, USA