1. D.L. Damiano, PT, PhD, is Chief, Functional and Applied Biomechanics Section, Rehabilitation Medicine Department, NIH Clinical Center, Bldg 10, Room 1–1469, Bethesda, MD 20892 (USA).
2. A.S. Arnold, PhD, is Research Associate, Concord Field Station, Harvard University, Bedford, Massachusetts.
3. K.M. Steele, MS, is a doctoral student in the Department of Mechanical Engineering, Stanford University School of Engineering, Stanford, California.
4. S.L. Delp, PhD, is Professor of Bioengineering and Mechanical Engineering, Stanford University Schools of Engineering and Medicine.