1. Department of Clinical Neurophysiology, Kuopio University Hospital, FI-70211 Kuopio, Finland
2. Department of Biomedical Engineering, Eindhoven University of Technology, 5600 MB, Eindhoven, The Netherlands
3. Department of Applied Physics, University of Eastern Finland, FI-70211 Kuopio, Finland
4. Division of Solid Mechanics, Department of Orthopaedics, Lund University, 221 00 Lund, Sweden
5. Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Alberta, BC, Calgary, Canada T2N 1N4