static optimization crash

[Julie Ellis]

Hi,
I'm working on a modified version of the Stanford upper extremity model looking at muscle work in a push up. I can get static optimization going with actuators and the results are pretty reasonable. But when I try to run it with the actuators + muscles it crashes. It shouldn't be an issue with strength, any ideas on why this might be happening? Thanks for any help.
Julie

[jimmy d]

Hi Julie,

The upper extremity kinematic model is difficult to work with in dynamics for a number of reasons (https://simtk.org/forums/viewtopic.php? ... 011151ef5e). The authors recently released a newer version for dynamic analysis that can be found here; https://simtk.org/home/upexdyn

I haven't used that model, so it would be good to post to their (the authors) forum for feedback.

Hope that helps,
-james

[Julie Ellis]

Thanks James,
We are using a modified version of the newer dynamic version, inverse dynamics seem to work well. The issue turns out to be a problem with the one of the lat muscles pennation angle. We had to reduce it quite a bit in order to get the static optimization to go.
Julie

[Dick Ameln]

Hi Julie, I am having the same issue with the dynamic Stanford model. When I try to run Static Optimization OpenSim crashes. Could you please tell me the specific changes you made to the LAT muscles to get it to run?

[Julie Ellis]

We reduced the pennation angle of all three lat muscles to 0.25. Also by running the optimization through matlab we seem to get better feedback when something does go wrong. We were finding that the optimization would stall or crash without producing error messages, but when run via matlab we get some better clues as to where the issue was. Hope this helps!
Julie