Physical load, psychosocial and individual factors in visual display unit work

Abstract

The overall aim of this thesis was to explore associations between physicalload, psychosocial and individual factors in visual display unit (VDU)work. Furthermore, the aim was to investigate whether perceived musculartension is a predictor of neck pain among VDU operators. The thesisis based upon five separate studies, two laboratory studies, two fieldstudies and one prospective cohort study.Several different methods were used to assess the physical load. Electromyography(EMG) was used to record muscle activity. Wrist postures andmovements were assessed by means of electrogoniometers. An instrumentedcomputer mouse was used to measure the forces applied to thecomputer mouse. Working technique was assessed with an observationprotocol. Perceived exertion, comfort, mental stress and perceivedmuscular tension were assessed with questionnaires.The results of this work are discussed in relation to a proposed model forVDU work and musculoskeletal symptoms. The first two studies (StudiesI and II) support an association between individual factors (workingtechnique and sex) and the physical load. In Study III we observed thatthe physical load increased as a result of mental stress and increasedproductivity. Besides an increase in muscle activity; increases in the forcesapplied to the computer mouse and increased repetitiveness of wristmovements were also observed. The results from the third study alsosupport an association between psychosocial factors and physical loadthrough increased physical demands. The fourth study (Study IV)supports an association between perceived muscular tension and physicalload and perceived muscular tension is hypothesized to be an early sign ofmusculoskeletal symptoms. In Study V an increased risk of developingneck pain was observed among subjects who perceived high musculartension, even when controlling for job strain, physical exposure and age.It is concluded that the physical load during VDU work is affected bypsychosocial and individual factors as well as physical demands. VDUusers who perceives muscular tension at least a few times per week appearto have an increased risk of developing neck pain.