1. a Dept. of Community Medicine and Rehabilitation , Physiotherapy, Umeå University , SE - 901 87, Umeå, Sweden
2. b Dept. of Public Health and Clinical Medicine , Occupational and Environmental Medicine, Umeå University , SE-901 87, Umeå, Sweden
3. c Dept. of Biomedical Engineering and Informatics , University Hospital of Northern Sweden , SE - 901 85, Umeå, Sweden
4. d Occupational and Environmental Medicine Sahlgrenska Academy and University Hospital, University of Gothenburg (UGOT) , Medicinaregatan 16, Box 414, 405 30, Gothenburg, Sweden