1M.E. Mueller Laboratory of Biomechanics, University of Bern, Bern, Switzerland
2Orthopedic Biomechanics Laboratory, Department of Orthopaedic Surgery, Charles A. Dana Research Institute, Beth Israel Hospital, 330 Brookline Avenue, Boston, MA 02215, U.S.A.
3Harvard Medical School, 330 Brookline Avenue, Boston, MA 02215, U.S.A.
4Department of Civil and Mechanical Engineering, M.I.T., Cambridge, MA 02139, U.S.A.
5Division of Applied Sciences, Harvard University. Cambridge. MA 02138. U.S.A.