1. Department of Physical Medicine and Rehabilitation, University of Colorado, 13121 East 17th Avenue, Mail Stop C244, Aurora, CO 80045 (USA)
2. Radboud University Medical Center, Radboud Institute for Health Sciences, IQ Healthcare, Nijmegen, the Netherlands
3. Physical Therapy Program, Department of Physical Medicine and Rehabilitation, University of Colorado
4. Physical Therapy Program, Department of Physical Medicine and Rehabilitation, University of Colorado; Geriatric Research Education and Clinical Center, VA Eastern Colorado Healthcare System, Denver, Colorado
5. Department of Epidemiology and CAPHRI Research School, Maastricht University Medical Centre, Maastricht, the Netherlands; and Top Sector Life Sciences & Health, Health-Holland, the Hague, the Netherlands