We have developed a model of the upper extremity that includes 15 degrees of freedom representing the shoulder, elbow, forearm, wrist, thumb, and index finger, and 50 muscle compartments crossing these joints. The kinematics of each joint and the force-generating parameters for each muscle were derived from experimental data. The model estimates the muscle–tendon lengths and moment arms for each of the muscles over a wide range of postures. Given a pattern of muscle activations, the model also estimates muscle forces and joint moments. The moment arms and maximum moment generating capacity of each muscle group (e.g., elbow flexors) were compared to experimental data to assess the accuracy of the model. These comparisons showed that moment arms and joint moments estimated using the model captured important features of upper extremity geometry and mechanics. The model also revealed coupling between joints, such as increased passive finger flexion moment with wrist extension. 

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The upper extremity model is shown in (A) a lateral view, (B) an anterior view, (C) a posteriolateral view, and (D) an anteriomedial view, demonstrating the degrees of freedom, muscle paths, and selected wrapping surfaces of the model (blue ellipses).

Associated Publications

Holzbaur, Murray, and Delp. "A Model of the Upper Extremity for Simulating Musculoskeletal Surgery and Analyzing Neuromuscular Control." Annals of Biomedical Engineering, 2005. (Download PDF)

Murray, Buchanan, and Delp. "Scaling of peak moment arms of elbow muscles with dimensions of the upper extremity." Journal of Biomechanics, 2002. (Download PDF)

Murray, Buchanan, Delp. "The isometric functional capacity of elbow muscles." Journal of Biomechanics, 2000. (Download PDF)

Gonzalez, Buchanan, and Delp. "How muscle architecture and moment arms affect wrist flexion-extension moments." Journal of Biomechanics, 1997. (Download PDF)

Delp, Grierson, and Buchanan. "Maximum Isometric moments generated by the wrist muscles in flexion-extension and radial-ulnar deviation." Journal of Biomechanics,1996. (Download PDF)

Murray, Delp, and Buchanan. "Variation of muscle moment arms with elbow and forearm position." Journal of Biomechanics, 1995. (Download PDF)