CMC failed for large knee ROM

[Lydia Willemse]

Hi,

I was trying the CMC tool for squatting and sit to stand transfer tasks using the fast optimization target. For both movements no solution was found by the optimizer for knee flexion angle below approximately 60 degrees.

I tried several possible solutions: making muscles twice as strong and increase reserve forces. Yet this wasn't helpful.

Reserves and residuals both have high control values so they are able to generate sufficient force.

Does anyone knows an explanation of why the failure occurs at these particular poses? I will be glad with advise how to deal with the failure.

Thanks in advance!

Lydia

[Glen Lichtwark]

Hi Lydia,

There could be a lot of things wrong, but one thing I would suggest is plotting the muscle lengths through the range of motion to make sure that there are any discontinuities (as a result of funny wrapping or jumping between via points) through the range. For large joint ranges of motion, there may be a point where the muscle is going through an unrealistically large length change in a very small amount of time.

Which model are you using?

Glen

[Ruoli Wang]

Hi Lydia,

I got similar CMC failure in squatting (gait2392.osim) when knee flexion angle reached around 60 degrees.

Code: Select all

SimTK Exception thrown at InteriorPointOptimizer.cpp:262:
Optimizer failed: Ipopt: Restoration failed (status -2)

Have you fixed the problem? I already tried to increase reserve and residual forces and muscle strength, nothing helped.

Thank you in advance,

Ruoli