1. S. van Twillert, PT, MSc, University Medical Center Groningen, Center for Rehabilitation, University of Groningen, Haren, the Netherlands.
2. K. Postema, MD, PhD, University Medical Center Groningen, Department of Rehabilitation Medicine, Center for Rehabilitation, University of Groningen, Groningen, the Netherlands.
3. J.H.B. Geertzen, MD, PhD, University Medical Center Groningen, Department of Rehabilitation Medicine, Center for Rehabilitation, University of Groningen, Groningen, the Netherlands
4. A.T. Lettinga, PT, PhD, University Medical Center Groningen, Center for Rehabilitation, University of Groningen, Haren, the Netherlands.