We have developed a seven segment, seven degree-of-freedom model of the human lower extremity to examine how surgical changes in musculoskeletal geometry and muscle architecture affect muscle force and its moment about the joints. This model represents a subject that is about 1.8 m tall and has the strength of a young, adult male. We defined the lines of action of forty-three muscle-tendon actuators based on their anatomical relationships to three-dimensional surface representations of the bones. A model for each actuator was formulated to compute its isometric force-length relation. The kinematics of the lower extremity were specified by modeling the hip, knee, ankle, subtalar, and metatarsophalangeal joints. Thus, the force and joint moment that each muscle-tendon actuator develops can be computed for any body position. The joint moments calculated with the model compare well with experimentally measured isometric joint moments. 

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Associated Publications

 Delp, Loan, Hoy, Zajac, Topp, Rosen. "An interactive graphics-based model of the lower extremity to study orthopaedic surgical procedures." IEEE Transactions on Biomedical Engineering, 1990. (Download PDF)

 Delp. "Surgery simulation: A computer-graphics system to analyze and design musculoskeletal reconstructions of the lower limb." Stanford University, Ph.D. Thesis, 1990. (Download PDF)