We would like to thank M.M.H.C Bijvelds, M.J.W. van Galen and A. Boekee, students at Fontys University of Applied Sciences, Department of Physiotherapy for support in patient measurements as well as F.A.M. Brooijmans, physical therapist, for using his equipment and practice. We also appreciate the assistance for patient recruitment and patient counselling of H.C.W. van Dalen, N. Verhofstad and P.P.H.L. Broos.