1. Department of Rehabilitation Medicine; Seoul National University Bundang Hospital, Seoul National University College of Medicine; 82, Gumi-ro 173, Bundang-gu, Seongnam-si Gyeonggi-do 13620 Republic of Korea
2. Department of Physical Medicine and Rehabilitation; Vanderbilt University Medical Center; Nashville Tennessee USA
3. Department of Physiology; University of Puerto Rico School of Medicine; San Juan Puerto Rico