1. Department of Rehabilitation Medicine, Clinical Center, National Institutes of Health, Bethesda, MD;
2. Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Korea;
3. National Rehabilitation Hospital, Seoul, Korea
4. Department of Rehabilitation Medicine, Clinical Center, National Institutes of Health, Bethesda, MD;Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, Daejeon, Korea