JOURNAL OF SOUND AND VIBRATION Journal of Sound and Vibration 298 (2006) 492–498 The association between whole body vibration exposure and musculoskeletal disorders in the Swedish work force is confounded by lifting and posture Mats Hagberg a,Ã , Lage Burstro¨m b , Anna Ekman a , Rebecka Vilhelmsson a a Occupational and Environmental Medicine, Sahlgrenska Academy and University Hospital, UGOT, Go¨teborg, Sweden b National Institute for Working Life—North, Umea˚, Sweden Received 7 May 2006; received in revised form 13 May 2006; accepted 8 June 2006 Available online 1 August 2006 Abstract This was a cross-sectional study based on material representing the Swedish work-force from a survey conducted in 1999, 2001 and 2003 by Statistics Sweden. Exposure to whole body vibration (WBV) was prevalent among agricultural, forestry, fishery workers and among plant and machinery operators based on a sample of 40,000 employed persons. Approximately 70% responders, that are 9798 persons answered both the interview and the questionnaire for the analysis of exposure–response. Exposure to WBV at least half the working time was associated with prevalence ratios above two for musculoskeletal symptoms in the low back, neck, shoulder/arm and hand among workers. When the exposure factors lifting and frequent bending were added to a multivariate analysis, surprisingly the magnitude of association was low between low back symptoms and WBV exposure. Interestingly, the relation between WBV exposure and symptoms in the neck, shoulder/arm and hand had the same or higher magnitude of association even when the possible confounders were in the model. For the neck, low back and shoulder/arm there was a visible increase in prevalence ratio (as high as 5 times) when combined exposures of WBV, lifting, frequent bending, twisted posture and noise were included in the analysis. r 2006 Elsevier Ltd. All rights reserved. 1. Introduction Whole body vibration (WBV) is mechanical energy oscillations which are transferred to the human body as a whole. This occurs usually through a supporting system such as a seat or platform. In a postal questionnaire to a random community sample Palmer and co-workers found that the most common sources of occupational exposure to WBV in the United Kingdom were cars, vans, forklift trucks, lorries, tractors, buses, and loaders [1]. In the European directive WBV means ‘‘the mechanical vibration that, when transmitted to the whole body, enters risks to the health and safety of workers, in particular lower back, morbidity and trauma of the spine’’ [2]. In a review by NIOSH 1997 the conclusion was that there was strong evidence for a positive association between exposure to WBV and back disorders [3]. A majority of studies reviewed in the NIOSH document demonstrated a dose–response relationship between exposure to WBV and low back disorders [3]. ARTICLE IN PRESS www.elsevier.com/locate/jsvi 0022-460X/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jsv.2006.06.024 Ã Corresponding author. Tel.: +46 31 77 36 305; fax: +46 31 40 97 28. E-mail address: mats.hagberg@amm.gu.se (M. Hagberg).