1. Department of Musculoskeletal Disorders and Physical Workload, The National Research Centre for the Working Environment , Lersø Parkallé 105, 2100 København Ø Denmark
2. Department of Occupational Health Sciences and Psychology, Centre for Musculoskeletal Research, University of Gävle , Kungsbäcksvägen 47, 801 76 Gävle , Sweden
3. Department of Public Health, University of Copenhagen , Øster Farimagsgade 5, 1353 København K , Denmark
4. Department of Sports Science and Clinical Biomechanics, University of Southern Denmark , Campusvej 55, 5230 Odense , Denmark