Static Optimization with muscles from MuscleExample

[Tylan Templin]

Hi OpenSim community,

I am trying to run a Static Optimization simulation using the FatigableMuscle model given in OpenSim 4.1\Resources\Code\CPP\MuscleExample.

I was able to create a plugin for the FatigableMuscle, load the plugin into the GUI, load the model with updated FatigableMuscles, and run Static Optimization. However, none of the muscle seem to be fatiguing.

The motion I am testing is going from a seated posture to a bent over posture and holding that posture for an extended period of time. Here is an example force output for a selection of back muscles in the model

Force_Profiles.PNG (10.77 KiB) Viewed 423 times

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I have changed the fatigue factor and recovery factor for the muscles to various values and have also run the simulation for longer time periods (up to 500 seconds) but continue to get the same results.

Any ideas why there isn't a decline in force output for these "fatigable" muscles?

Thanks!

Ty

[Thomas Uchida]

Any ideas why there isn't a decline in force output for these "fatigable" muscles?

Was the model designed to be used with Static Optimization? There is a description of the model here: https://simtk-confluence.stanford.edu:8 ... ble+Muscle. Given that Static Optimization does not integrate forward in time, I suspect that you would need to modify the muscle model to use it in this condition.

[Tylan Templin]

Thank you! I was hoping to use Static Optimization because it solves relatively quickly, but that makes sense that the muscle won't fatigue with SO because there is no forward integration. CMC seems to work just fine other than taking quite a bit longer.

Thanks again,

Ty