Those file sizes seem very large. How long are your experimental trials? If you have a very long experimental trial, then you may want to break it up into a number of smaller trials to help with analysis.

You can run an analysis that includes a force reporter. The force reporter can output the bushing forces.

Are the errors reported in degrees? As in-- the peak error you are seeing is ~0.055 of a degree?

The OpenSim WIki is a good place to start. There are also some good papers out there to read, including the this one.

The API for many Classes (like the ScaleTool) were changed between 3.3 and 4.0 since it was such a major release. You can view the API documentation for the ModelScaler, here . In 4.0, there is also a new run() method on ScaleTool , reducing the requirement to process the model in the ModelScaler or...

I would suggest posting a zip of all the files needed to recreate the issue. It could be poor kinematics, forces, model scaling, muscle scaling.

If you haven't yet, perhaps have a look at that Static Optimization tutorial , it discusses jagged activations. There also could be discontinuities in either your kinematics or, if the jumps are around heel strike or toe-off, due to the forces (thus accelerations) changing suddenly. There have been ...

I started a new topic for your issue because it wasn't related to the original thread. You should check the MVN documentation and reach out to Xsens user support. Xsens can output the raw IMU data in txt file format and that is what the OpenSim IMU data converters. Otherwise, you will have to write...

You may want to start with the markers-- all of your markers are connected to "ground" and not to model bodies.

Details about the modeling choices for the Thelen2013 muscle can be found here. The choice of default values, like minimum activation, were choosen to reduce numerical singularities.