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open sim inverse dynamics external loads

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  • open sim inverse dynamics external loads


    My group and I are working on a musculoskeletal model of the spine in opensim. We are all fairly beginner here and have been running through the tutorials, looking at the confluence web-site etc.

    We have a generalized model developed from the literature, and as a result we do not have external load data, such as force plates, etc.

    In fact the model does not go to the feet, but stops at the pelvis.

    We are attempting to solve an inverse dynamics problem and determing the internal loads/torques at the joints of the spine. We are able to do so, but have left "unchecked" the external load tab, because we do not have external loads.

    Is our output of internal forces/torques just junk because we do not have applied forces? Without applied forces how is it even able to solve at all? The only thing I can think of, is that gravity is incorporated through the center of mass and is the applied force.

    Any help is appreciated.


  • #2
    Re: open sim inverse dynamics external loads

    Hi Brandon,

    You may also want to post your question to the OpenSim discussion forum located here:

    Director, Simbios
    Director of Dissemination and Training, NCSRR


    • #3
      Re: open sim inverse dynamics external loads

      For validating your model, you need to do inverse dynamics analysis and that will need external forces. For spine only model, I guess there is no way to apply and measure external forces. You will need some end effector parts to be added into your model, like pelvis and hips, so that you could measure forces and moments, by some method, like an instrumented chair, for simple tasks like turning, bending, to compute forces and torques being generated at individual spinal joints. The model could be validated through Forward dynamics analysis on your model, applying computed forces and torques in Inverse Dynamics analysis at individual joints, and comparing resulting motions and external forces with mesured quantities.


      • #4
        Re: open sim inverse dynamics external loads

        For those following this question, a discussion chain has been started on the OpenSim user forum:

        Best wishes,
        Jen Hicks
        OpenSim R&D Manager