The prevalence of computer use is rapidly increasing, with a corresponding rise in computer related musculoskeletal disorders. The main risk factors associated with keyboard and mouse use are static and awkward postures of the upper extremity and the repetitive nature of keyboard and mouse tasks.
The aim of this thesis was to examine two issues related to computer use, symptom prevalence related to mouse use and the use of forearm support during keyboard and mouse use. The overall goal of the thesis was to provide recommendations for workstation setup and working posture for computer use.
An epidemiological study was conducted to determine the whether a relationship existed between computer mouse use and musculoskeletal symptoms in a sample of 270 mouse users. No relationship was found between hours of mouse use per day and reported symptoms. A relationship was found between the variable of arm
abduction, which is specific to mouse use and symptoms in the neck. The findings of this study support the hypothesis that mouse use may contribute to musculoskeletal injury of the neck and upper extremity. Mouse users are exposed to the same recognised risk factors associated with keyboard use as well as the additional risk factor of arm abduction during mouse use. Work in arm abduction is a risk factor for neck/shoulder musculoskeletal disorders.
Forearm support during keyboard use has been reported to reduce neck and shoulder muscle activity and discomfort. However, the effect of forearm support on wrist posture during keyboard and mouse use was unknown. The aim of the first laboratory study was to examine the effect of forearm support on wrist posture. Thirteen participants completed 20 minute word-processing tasks in each of three postures: forearm support, wrist support and no support (floating). Electromyography was used to monitor neck, shoulder and
forearm muscle activity. Bilateral and overhead video cameras recorded wrist, shoulder and elbow angles. Forearm support resulted in significantly less ulnar deviation, reduced time spent in an extreme wrist posture and fewer reports of discomfort than the "floating" posture. Wrist support resulted in reduced trapezius and anterior deltoid muscular activity.
The aim of the second laboratory study was to examine the effect of wrist rests on wrist posture, muscle activity and discomfort when used in conjunction with forearm support during keyboard and mouse use. Fifteen participants used a keyboard for 15 minutes with and without use of a wrist rest. Mouse use with and without a wrist rest was examined during 2 minute tasks. Electromyography was used to monitor neck and shoulder muscle activity. Bilateral electrogoniometers recorded wrist flexion/extension and deviation. Minimal differences were found as a result of wrist rest use. Left wrist
extension was significantly less for keyboard use when a wrist rest was used. No other significant differences in muscle activity or wrist angles were found for either keyboard or mouse use when a wrist rest was used.
The laboratory studies indicate that provision of forearm support using a conventional desk may be beneficial for both keyboard and mouse users, irrespective of whether or not a wrist rest is used. The aim of the final study was to determine whether providing forearm support when using a normal computer workstation would decrease musculoskeletal discomfort in intensive computer users in a call centre. In a randomised controlled study (n=59), thirty participants were given forearm support for 12 weeks and the remainder were given forearm support for the last 6 weeks of the study (control group). Questionnaires were used to obtain information about discomfort, workstation setup, working posture and comfort. Nine participants withdrew within a week
of commencing forearm support either due to discomfort or difficulty in maintaining the posture. At 12 weeks, both groups reported a significant decrease in neck, back and wrist symptoms.
The findings of this thesis indicate that forearm support may be preferable to the "floating" posture implicit in current Australian guidelines for computer workstation setup. A review of the current literature on workstation setup and working posture confirmed these findings, but highlighted the importance of the need for consideration of individual differences and the provision of guidelines regarding a variety of "safe and healthy" work practices rather than one prescriptive working posture.