Actuator range for static optimization

[Tim Dorn]

Hi,
How do we change the actuator range in a static optimization analysis when there appears to be no controlconstraints file tag in the static optimization analysis setup file?

Cheers!

[Lisa MacFadden]

I too am interested in learning if this is possible. Specifically I am interested in changing the minimum activation level for two or three muscles in my model while leaving the rest with the normal activation ranges for static optimization.

[Ayman Habib]

Tim,

There are no constraints specified to Static Optimization. For muscles it goes (.01 to 1.0 * max-isometric-force ) and for everything else it goes (-1 to 1 * max-force/torque). If you need to make a muscle stronger you need to increase the max-isometric-force.

If you select "use-muscle-physiology" then force computation uses the muscle's force-length curve.

Hope this helps,
-Ayman

[Lisa MacFadden]

Ayman,

Is there a way to set the range for individual muscle activations - for example say i have two muscles, can i say that muscle1 can have the full range of activation 0.01 to 1.0 and have muscle2 constrained such that it can be activated from 0.5 to 1.0 (during static optimization).

Cheers
Lisa

[Ayman Habib]

Lisa,

These bounds are hard-coded in the Static Optimization tool, so for now no "easy" way around it.

Best,
-Ayman

[daniel jaramillo]

Hello Dr Ayman,

I have increased the max-isometric force for each muscle and increased the optimal force of MX, MY and MZ but still get the same error, "The model appears to be too weak, MX approaching lower bound of -1, MY approaching lower bound of -1".

Thankyou,
Daniel

[Ayman Habib]

Daniel,

Did you run Inverse Dynamics to check what kind of Forces/Torques are required to reproduce the motion? That would be the first step.

If there's something wrong with the model/setup/grf-specification you'd see it immediately.

-Ayman

[daniel jaramillo]

Hello Dr Ayman,

I ran the Inverse Dynamics and compared the results to those from the gait 2354. The main differences were in the pelvis_ty. I tried modifying the optimal forces to the muscles in the hip groups, but it still shows me the same error as before.

Thank you for your time,

Daniel Jaramillo

[Ayman Habib]

Daniel,

If inverse dynamics tells you that you need some specific value for (FX, FY, FZ, MX, MY, MZ) then adding reserves that can provide these Forces/Torques should definitely make it (Static Optimization) work unless there's something wrong with the setup. How big are these in InvereseDynamics solution anyway? Are you sure your ground reactions are specified correctly?

-Ayman

[daniel jaramillo]

Helo Dr Ayman,

The values from the InverseDynamics for pelvis_ty range from 250 to 475. I dont know exactly what you mean by "specified correctly", well I did not include the file in the External loads section of the GUI. The data was obtained using Visual3D and for what I understood, it is supposed to be included in the .mot file.

Thankyou for your time,

Daniel Jaramillo