1. Department of Public and Occupational Health; EMGO Institute for Health and Care Research; VU University Medical Center; Amsterdam The Netherlands
2. Centre for Research in Childhood Health; Institute of Sports and Clinical Biomechanics; University of Southern Denmark; Odense M Denmark
3. Orthopaedic dep. Hospital of Lillebaelt and Institute of Regional Health Services Research; The Sport Medicine Clinic; University of Southern Denmark; Lillebaelt Denmark