1. Graduate School of Systems & Information Engineering, University of Tsukuba, Tsukuba, Japan
2. Institute of Medicine, and Center for Cybernics Research, University of Tsukuba, Tsukuba, Japan
3. Institute of Systems and Information Engineering, University of Tsukuba, Tsukuba, Japan
4. Department of Orthopaedic Surgery, Institute of Medicine, University of Tsukuba, Tsukuba, Japan