Exposure to keyboard/mouse use = keystrokes + mouse clicks + POSTURE - a missing variable that cannot be overstated
Self-report of duration of computer use is usually overestimated. The search for a valid measure of exposure to keyboard/mouse use resulted in the development of a computer registration software. The use of this new software generated unexpected results when IJmker et al.1 found software- recorded computer use was not significantly associated with upper extremity/neck symptom onset while self-reported computer use was signficantly associated with symptoms in the neck/shoulder and arm/hand. What is captured in the self-report that is missing in the software- recorded duration of computer use? In the editorial by Gerr and Fethke2 reference is made to work by Homan and Armstrong3 that noted the potential negative effect of time spent with hands held over the keyboard but without keying. In our Medical-Ergonomic Program4 we refer to this position as the 'action ready' posture when the forearm(s) is in full pronation over the keyboard or mouse causing muscle activation of the forearm extensor muscles. This may lead to the development of painful trigger points in the forearm extensor muscles, a common area of complaints by computer users.4 Activities such as reading, talking, thinking etc. while using the computer are frequently accompanied by this 'action ready' posture. Time spent in these activities is included when self-reporting duration of computer use but would not be captured in computer registration software.
Other posture issues without keystrokes or mouse clicks involve the neck/shoulder area. Computer users have a habit of not sitting up straight against the back of the chair and carry their shoulders forward. This posture activates the muscles involved with scapulae stabilization and shortens the pectoralis minor4 resulting in painful trigger points in the overused muscles . Neck/shoulder muscles are also activated when mouse use is with the arm extended away from the body, when the monitor is too far away and the chin juts forward or when the keyboard is too high and the shoulders remain hiked to compensate. Maintenance of these postures with or without keystrokes and mouse clicks are an etiology for upper extremity symptoms that needs to be added to the exposure equation for computer use.
1. IJmker S, Huysmans MA, van der Beek AJ, et al. Software-recorder and self-reported duration of computer use in relation to the onset of severe arm-wrist-hand pain and neck-shoulder pain. Occup Environ Med 2011;68:502-209.
2. Gerr F and Fethke N. Ascertaining computer use in studies of musculoskeletal outcomes among computer workers: differences between self- report and computer registration software. Occup Environ Med 2011;68:465- 466.
3. Homan MM and Armstrong TJ. Evaluation of three methodologies for assessing work activity during computer use. AIHA J (Fairfax, VA) 2003;64:48-55.
4. Bleecker ML, Celio MA, Barnes SK. A medical-ergonomic program for symptomatic keyboard/mouse users. JOEM 2011;53:561-567.
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