(Dr. John Wu, 21. May, 2008 )
Since musculoskeletal disorders of the upper extremities are believed to be associated with repetitive excessive muscle force production in the hands, understanding the time-dependent muscle forces during key tapping will help to explore the mechanisms of disease initiation and development. In the current study, we analyzed the dynamic muscle forces in an index finger during typing using a universal finger model developed on a platform of AnyBody. Seven muscles were included in the proposed model: flexor digitorum profundus (FP), flexor digitorum superficials (FS), extensor indicis (EI), extensor digitorum communis (EC), radial interosseous (RI), ulnar interosseous (UI), and lumbrical (LU). The time histories of impact force at the fingertip in the published studies are applied to drive the model. Our analysis indicates that the power generated by FP, EC, and EI muscles are predominant among all muscles, while the power generated in MCP joint is predominant among all three joints. The predicted time-histories of muscle forces agree well with the EMG measurements in the literature. Our results suggested that the muscle force is mainly induced by the impact force at the fingertip during tapping, rather than due to the mass moment inertia of the finger section.
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