1. Rehabilitation Engineering Lab, Department of Kinesiology and Community Health, University of Illinois at Urbana-Champaign, Urbana, IL, USA
2. College of Physical Education and Sports, Beijing Normal University, Beijing, China
3. Department of Physical Education, Peking University, Beijing, China
4. College of Liberal Arts and Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, USA