1. John A. Paulson School of Engineering and Applied Sciences and Wyss Institute for Biologically Inspired Engineering, Harvard University, Cambridge, MA 02138, USA.
2. Mechanical Engineering Department, Chung-Ang University, Seoul 06974, Republic of Korea.
3. Department of Biomechanics and Center for Research in Human Movement Variability, University of Nebraska Omaha, Omaha, NE 68182, USA.