Missing Joint Powers and Moments

[Ben Perrin]

Hello,

I am currently running planar jumping simulations with a fairly simple model. I am hoping to look at joint powers, however I've found that only the most proximal (hip) and distal (MTP joint) joints have any information. The rest of the joints are simply flat-lined at zero for the entirety of the jump despite the fact that kinematics are about as expected. Could you provide some insight into how these values are calculated and how the relate to joint accelerations (as they don't appear to match in this case)? Are there any possible fixes that you can think of for this?

Thank you so much for all of your help, I really appreciate it!

[Thomas Geijtenbeek]

Are you using an OpenSim model or a Hyfydy model?

[Ben Perrin]

I'm using an OpenSim4 model.

[Thomas Geijtenbeek]

I looked into it, but I'm using the standard OpenSim API to compute the moment, moment arm and dof velocity. Is the moment, moment_arm or dof velocity also zero in your data?

[Ben Perrin]

Moments for every joint besides the hip and MTP joint are zero.

There are not many relevant moment arms in the output, as nearly all are listed for joints that the muscle does not cross (e.g., hamstring moment arm about the ankle). This felt strange, however I can't tell if it's the source of the issue or an effect of it.

The dof velocities however, are non-zero and look about how I would expect them to. I would be happy to share any of the outputs/code if that would help.

[Thomas Geijtenbeek]

It seems like an issue with OpenSim, since I'm directly calling their API to compute the muscle moment arm:

https://github.com/tgeijten/scone-core/ ... 4.cpp#L166

This is beyond my reach, unfortunately. For in-dept support with regards to the simulation engine, please consider using Hyfydy:

https://scone.software/doku.php?id=hyfydy

[Ben Perrin]

I will look into that, thank you for you help!