Muscle forces in upper extremity model

[Kamal Gautam]

Hi,

I am looking to estimate the muscle force for the elbow flexion (from 0 to 90 degree) with the muscle force generation capacity of 50th percentile man.
I have used the Upper Extremity Dynamic Model (latest one). I have gone through the tutorial and made a similar motion file that includes all the dependent and independent coordinates for the elbow flexion motion, ideally I assumed that the elbow flexed from 0-90 in 1 sec and hold in that position for 0.5 sec. When I load the motion file, I can see the desired animation of the model.
Then, I run an inverse dynamic to calcualte the elbow flexion moments the results are shown in the attached figure. I have a negative moment initially, then rises to positive value as the elbow flexion angle increases and remains steady when the elbow is hold at 90 degree for a while.
Then, I used that result to estimate the muscle force using static optimization. But I got an errors at every time steps as follow:

SimTK Exception thrown at InteriorPointOptimizer.cpp:264:
Optimizer failed: Ipopt: Infeasible problem detected (status 2)
OPTIMIZATION FAILED...
StaticOptimization.record: The optimizer could not find a solution at time = 0.85.
The model appears too weak for static optimization.
Try increasing the strength and/or range of the following force(s):
SUBSC approaching upper bound of 1
TMIN approaching upper bound of 1
TMAJ approaching upper bound of 1
PT approaching upper bound of 1

I am new to this and gone throught the documentations and tutorial example. But not able to deal with it. So, any help/suggestion with how to eliminate this error will be appreciated.

Thank you.

[Carmichael Ong]

One place to start is going over the documentation page "Simulation with OpenSim - Best Practices" and looking under the section on Static Optimization: https://simtk-confluence.stanford.edu:8 ... +Practices

Other things to check:
- Go back to the paper describing the model you're using and see what the ranges of motion that they have validated the model and make sure you are within those ranges.
- You could also check if there are excessive passive forces that would lead to needing large active forces to compensate.