1 John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.
2 Wyss Institute for Biologically Inspired Engineering, Harvard University, Cambridge, MA 02138, USA.
3 Department of Biomechanics and Center for Research in Human Movement Variability, University of Nebraska at Omaha, Omaha, NE 68182, USA. walsh@seas.harvard.edu pmalcolm@unomaha.edu.
4 John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA. walsh@seas.harvard.edu pmalcolm@unomaha.edu.