1. G Kwakkel, PhD, is Physiotherapist and Human Movement Scientist, Department of Physical Therapy and Research Institute for Fundamental and Clinical Human Movement Sciences, University Hospital Vrije Universiteit, PO Box 7057, 1007 MB Amsterdam, the Netherlands.
2. RC Wagenaar, PhD, is Chairman, Department of Physical Therapy, and Director, Center for Neurorehabilitation, Sargent College of Health and Rehabilitation Sciences, Boston University, Boston, Mass