Irving S. Scher, Ph.D., P.E., Principal at Guidance Engineering and Affiliate Scientist in the Applied Biomechanics Laboratory at the University of Washington, Seattle, Washington, USARichard M. Greenwald, Ph.D., President of Simbex, Lebanon, New Hampshire, USA, and Adjunct Professor, Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, USANicola Petrone, Ph.D., Department of Industrial Engineering, University of Padova, Italy.