Editing .mot/.sto files and External Loads

[Blakely Keeling]

I am working on a research project where I am using a Gait2354osim model. I want to create an isometric movement where the person is sitting and slightly extends their leg against a bar. Is is possible to edit a motion data file in a way so that OpenSim will execute the motion that I am trying to achieve? For example, a gait motion to the previously described motion. Most of the documentation that I have seen talks about associating the motion data with the model, but not necessarily editing it to achieve a different desired motion. Is this only achievable by using motion capture footage with a separate program? Or can I use the simulate button in the program and edit that? Also I am trying to edit the external force data. I have acceleration data from iWorx and no motion capture data. How can I edit the motion and force in such a way that Opensim will run? I have tried changing the files in a XML editor then loading them into OpenSim, but it does not run.

Thanks,
Blakely K.

[Carmichael Ong]

You can definitely open the .mot and .sto files in Excel or a text editor and change the values that way. These files are tab-delimited files. You could also use MATLAB or Python to adjust these files too. One thing to note, though, is that if you change the kinematics and you don't change the external forces, then you may have dynamic inconsistencies between your motion and the force plate data (and vice versa if you only change the external loads data without the corresponding kinematics).

Another way you could create an isometric movement is do pose the model in the position you'd like, lock all of the degrees of freedom, and then do a short forward dynamics simulation. The output should then be an isometric motion printed to file.