1. Division of Gerontology and Geriatric Medicine, Department of Medicine, University of Maryland School of Medicine, 10 North Green Street, BT/18/GRECC, Baltimore, MD 21201, USA
2. Geriatric Research, Education and Clinical Center, Baltimore Veterans Affairs Medical Center, Baltimore, MD 21201, USA
3. Department of Physical Therapy, University of Utah, Salt Lake City, UT 84108, USA
4. Department of Exercise and Sport Science, University of Utah, Salt Lake City, UT 84112, USA
5. Department of Orthopedics, University of Utah, Salt Lake City, UT 84108, USA