Objective: The purpose of this study was to design and test alternative computer mouse designs that attempted to reduce extensor muscle loading of the index and middle fingers by altering the orientation of the button switch direction and the force of the switch. Background: Computer users of two-button mouse designs exhibit sustained lifted finger behaviors above the buttons, which may contribute to hand and forearm musculoskeletal pain associated with intensive mouse use. Methods: In a repeated-measures laboratory experiment, 20 participants completed point-and-click, steering, and drag tasks with four alternative mouse designs and a reference mouse. Intramuscular and surface electromyography (EMG) measured muscle loading, and movement times recorded by software provided a measure of performance. Results: Changing the direction of the switch from a conventional downward to a forward design reduced (up to 2.5% maximum voluntary contraction [MVC]) sustained muscle activity (10th percentile EMG amplitude distribution) in the finger extensors but increased (up to 0.6% MVC) flexor EMG and increased movement times (up to 31%) compared with the reference mouse (p < .001). Implementing a high switch force design also increased flexor EMG but did not differ in movement times compared with the reference mouse (p < .001). Conclusion: The alternative mouse designs with altered switch direction reduced sustained extensor muscle loading; however, trade-offs with higher flexor muscle loading and lower performance existed. Application: Potential applications of this study include ergonomic and human computer interface design strategies in reducing the exposure to risk factors that may lead to upper extremity musculoskeletal disorders.
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