1. F. Ambrosio, PT, MPT, is a guest co-editor of this special series. She is associate professor, Department of Physical Medicine & Rehabilitation and the Departments of Physical Therapy, Orthopaedic Surgery, and Microbiology & Molecular Genetics, and the McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania.
2. J.A. Kleim, PhD, is a guest co-editor of this special series. He is associate professor, School of Biological and Health Systems Engineering, Arizona State University, Tempe, Arizona.