E M Roos1, M A Risberg2, C B Little3. 1. Center for Muscle and Joint Health, Department of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark. Electronic address: eroos@health.sdu.dk. 2. Department of Sport Medicine, Norwegian School Sport Sciences and Division of Orthopedic Surgery, Oslo University Hospital, Norway. 3. Raymond Purves Bone and Joint Research Laboratory, Kolling Institute, University of Sydney at Royal North Shore Hospital, St Leonards, NSW, Australia.