What tools to use?

[Valentina Gallego]

Hello again,
Right now i'm working on a project to evaluate a person performance while doing a squat exercise with regular weights and with an exercise device, for this I have motion capture data, Joint angles, ground reaction forces and other external loads. i would like to know if I have to go trough all the tools one by one (Scaling, IK, ID, SO, RR, ...) to get good information about the muscles and joint reaction forces or which ones should I use?
It's not very clear to me what are the results, pros and cons of each tool.

Thanks!!!

[Thomas Uchida]

An appropriate workflow can depend on the research question, model, experimental data, etc. You will need to scale your model if it hasn't already been scaled. You have stated that you already have joint angles---how were these computed? You may want to use the IK Tool if your joint angles were computed without a (constrained) model. You can use RRA to adjust the mass and mass center location of body segments where these properties are not known precisely (but can substantially affect residuals). You can find this information on the following pages in the Confluence documentation:
- "Overview of the OpenSim Workflow": https://simtk-confluence.stanford.edu/d ... m+Workflow
- "Scaling": https://simtk-confluence.stanford.edu/d ... im/Scaling
- "Inverse Kinematics": https://simtk-confluence.stanford.edu/d ... Kinematics
- "Residual Reduction Algorithm": https://simtk-confluence.stanford.edu/d ... +Algorithm

You might also want to check the Methods sections of papers that have generated similar simulations. Another good place to start would be to work through the tutorials and some of the examples here: https://simtk-confluence.stanford.edu/d ... +Tutorials.

[Valentina Gallego]

Thank you very muck! what do you mean by " if your joint angles were computed without a (constrained) model."

[Thomas Uchida]

what do you mean by " if your joint angles were computed without a (constrained) model."

You mentioned that you already have joint angles but you didn't indicate how you computed them. OpenSim's IK Tool uses a model of the skeleton to compute joint kinematics from mocap data, so even though you've already computed them somehow, you may want to compute them again in OpenSim.

[Valentina Gallego]

They where computed using another IK solver since I only have about 14 markers and openSim did a weird solution for it. when I load that motion (the one of the external solver) it seems to make sense with the motion being made (this motion is already filtered). also the openSim skeleton is scaled the same way the other solver did. Do you think the ID solution and SO will have a big repercussion on that?