Assessment of physical work load at visual display unit workstations : ergonomic applications and gender aspects

Local physical workload at visual display unit (VDU) workstations with different lay-out and computer input devices were studied among men and women. Word processing with keyboard only and a computer mouse were compared. "Mouse" operators worked longer time in strenuous working postures than "non-mouse" operators and they corrected a longer text during the given time. The intra- and inter-method reliability of a questionnaire for estimation of physical load in word-processing work was tested. Self-reported duration of VDU work and mouse use had a good intra-method reliability, and self-reports on location of keyboard and mouse on the work table had a good inter-method reliability when compared with direct measurements. In a cross-sectional study female CAD-operators reported a higher prevalence of musculoskeletal symptoms than their male colleagues despite the same education/training, work content and self-reported physical load. Location of the mouse outside an "optimal" area on the work table and/or long duration of mouse use were associated with higher prevalence of upper limb symptoms. An experimental study was designed to determine posture, muscular load and perceived exertion with six different locations of the computer mouse on the work table. A mouse location on the worktable corresponding to a relaxed, neutral posture of the arm combined with arm support was preferred. Arm support also reduced muscle load in the neck/shoulder region. Comparison of text editing with a mouse and a track-ball showed that work with the track-ball entailed lower shoulder elevation and less shoulder muscle activity, but more wrist extension than work with the mouse. Gender differences in working techniques were observed in the experimental studies and should be subject to further analyses. Development, specification and evaluation of a work table, suitable for VDU work with a non-keyboard computer input device, i.e. a mouse was carried out in collaboration with furniture manufactures, employees and employer. It was shown that the layout of a VDU work table, suitable for work with different input devices should make it possible to support the arms, to vary between sitting and standing postures and to prevent pronounced abduction and outward rotation of the shoulder.