An evaluation of visual display unit placement by electromyography, posture, discomfort and preference

Abstract

Due to a dramatic increase in musculoskeletal disorders relating to computer use, a number of ergonomics recommendations have been proposed in order to combat this problem. However, some of these recommendations have been conflicting, for example, visual display unit (VDU) monitor placement. This study aimed to investigate the effects of monitor placement in a group of normal subjects. Ten male and ten female subjects within the working age range volunteered to perform a computing task for 20 min in two different VDU monitor placement conditions; high monitor position (HMP) and a low monitor position (LMP). Postural angles (gaze, head, neck, and trunk), normalised electromyography (upper trapezius and cervical and thoracic erector spinae), discomfort (upper body), and individual preference for monitor placement were determined. The results indicated that the gaze, head, neck, and trunk angles in the LMP were significantly greater (more flexed) than those in the HMP. There was a trend for lower levels of electromyographic (EMG) activity for trapezius in the HMP. There were significantly lower levels of EMG activity for cervical and thoracic erector spinae in HMP. There was no difference between the monitor placement conditions on the basis of discomfort ratings. Twelve subjects preferred the HMP compared to 7 for LMP, whilst 1 had no preference. The results of this study suggested that subjects may use a less flexed head, neck and trunk posture and less cervical and erector spinae muscle activity when working with a HMP. However, the compromise between musculoskeletal and visual criteria over prolonged work periods requires further research before a recommendation for VDU height can be justified. Relevance to industry: Visual display units are widely used in all industries. The optimisation of their placement is a critical aspect of the human-machine interaction impacting on worker health, satisfaction and performance. (C) 2000 Elsevier Science B.V.