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Objective: To assess the impacts of postural and visual stressors on musculoskeletal and visual function during computer use.Background: Computer use involves low level static exertions that may be influenced by the postural and visual parameters of the workstation. The mechanisms of musculoskeletal pain and visual discomfort underlying low level static exertions, such as those experienced during computer work, are poorly understood. It was hypothesized that static postural and visual stress experienced during computer work might synergistically contribute to trigger point development, resulting in myofascial pain, as well as symptoms of eyestrain.Methods: Twelve subjects (six male and six female) participated in a study that simulated computer work. Each subject participated in three separate one-hour sessions, performing a typing task under high and low postural and visual stress conditions. Musculoskeletal measures included trigger point development monitored via expert opinion and self-report, electromyographic (EMG) activity, as well as self-reported discomfort. Cyclic changes in the EMG median frequency, representative of motor unit rotation, as well as a central tendency measure were used to assess EMG activity at multiple muscle locations on the trapezius. Hence, a multi-channel array was used to monitor EMG differences between muscle spatial locations relative to the trigger point. Visual measures included EMG activity of the orbicularis oculi, blink rate, accommodation, and self-reported visual discomfort.Results: Myofascial trigger points developed in all subjects regardless of the stress condition. The most interesting finding was the interaction between postural and visual factors on both the musculoskeletal and visual systems. Both high postural and high visual stress conditions resulted in significantly fewer cyclic changes in median frequency (i.e. less motor unit rotation) across the trapezius, and reduced blink rate compared to the baseline low stress condition. Spatial location relative to the trigger point site on the trapezius also influenced EMG patterns.Conclusions: Results have shown the importance of considering both postural and visual factors in order to understand the nature of the health effects associated with computer work. Disorders related to this type of work may be influenced by the complex interaction between the physical and visual parameters of the task.A hypothesized injury pathway model leading to myofascial pain, MSDs, and visual system disturbances during computer work was presented. A central stress theory involving the autonomic nervous system was proposed to be the interactive mechanism affecting both musculoskeletal and visual loading. However, efforts to further understand the mechanisms through which this interaction occurs are needed. |
