1. State Key Laboratory of Virtual Reality Technology and System, School of Biological Science and Medical Engineering, Beihang University, Beijing, China
2. Department of Rehabilitation, Affiliated Hospital of Binzhou Medical College, Binzhou, Shandong, China
3. Department of Kinesiology and Community Health, Rehabilitation Engineering Laboratory, University of Illinois at Urbana--Champaign, Urbana, IL, USA
4. Key Laboratory of Human Motion Analysis and Rehabilitation Technology of the Ministry of Civil Affairs, School of Biological Science and Medical Engineering, and the State Key Laboratory of Virtual Reality Technology and System, Beihang University, Beijing, China