Open Access. The published version of this work has been reproduced here according to the policies of American Physical Therapy Association. This article may be downloaded for personal use only. Permission to reproduce this article must be sought from the American Physical Therapy Association. This article was first published in the Physical therapy, 81(7): 1351-1358, 2001. The original published version can be found at http://ptjournal.apta.org/content/81/7/1351.full. Copyright (2001) American Physical Therapy Association.