Static Optimization Results not like expected

[Niklas Rudolph]

Hello,
I'm trying to get the lower extremity muscle forces for patient specific parameters.
The static optimization is run using the default files included in the rescources, but my forces are only in the range of 6 to 30 Newtons while I expected around 300 Newtons.

A force curve I got from my SO:

20210322_Forces_Glut_Max.png (15.62 KiB) Viewed 430 times

Literature, also used OpenSim, this is what I expected:

20210322_Forces_Glut_Max_Paper.png (21.2 KiB) Viewed 430 times

I suspect the actuator file I'm using might be wrong, but don't really know how to get or make a good one, any sources for that? Right now I'm using the actuators from the RRA Example provided in the resources.

subject01_Setup_SO.xml

(5.26 KiB) Downloaded 9 times

gait2392_RRA_Actuators.xml

(32.95 KiB) Downloaded 14 times

Any idea where I could look to fix this?

Thank you.

[Carmichael Ong]

The actuators file might be one of the issues. For RRA, you want high "optimal_force"s for your additional Actuators because those are the ones that drive the motion (muscles are not used in RRA). For Static Optimization, these actuators are there only to supplement the muscle forces, but you want the muscles to drive the motion. Thus, you want to have low "optimal_force"s (try in the range of 1Nm)

[Jacob J. Banks]

Opensim >4.0 comes with a nice Matlab function to generate reserve actuator files. Look in your PC's Documents\OpenSim\Code\Matlab\Examples for "createActuatorsFile.m" or see attached (if you downloaded <4.1). Note: I'm unsure if this function will work with 3.3.