1. S. Romkema, OT, MSc, Department of Rehabilitation Medicine, University Medical Center Groningen, University of Groningen, Hanzeplein 1, NL-9700 RB Groningen, the Netherlands.
2. R.M. Bongers, MSc, PhD, Center of Human Movement Sciences, University Medical Center Groningen, University of Groningen.
3. C.K. van der Sluis, MD, PhD, Department of Rehabilitation Medicine, University Medical Center Groningen, University of Groningen.