Scapulothoracic joint model and muscles

[yoann blache]

Dear Opensim community,

I am currently using the new Scapulothoracic joint model. I started to add muscles to this model (from the DELFT shoulder model). However when I try to perform static optimization (arm elevation in the scapular plane), some errors appear:

The model appears unsuitable for static optimization.
Try appending the model with additional force(s) or locking joint(s) to reduce the following acceleration constraint violation(s):
clav_prot: constraint violation = -0.044468
clav_elev: constraint violation = -0.0430865
scapula_abduction: constraint violation = -0.0037917
scapula_elevation: constraint violation = 0.18018
scapula_upward_rot: constraint violation = 0.00403066
scapula_winging: constraint violation = -0.0443211
shoulder_elv: constraint violation = -6.11226e-006
plane_of_elev: constraint violation = -4.62358e-006
axial_rot: constraint violation = 1.74277e-006
elbow_flexion: constraint violation = -6.60464e-006
pro_sup: constraint violation = 2.06151e-005

If I remove all the muscles, the static optimization runs perfectly with residuals actuactors. As soon as I add ONE muscle (no wrapping) the above error message appears ... even if I let the residual activators.

I would like to know if this problem could be solved .


Best regards

Yoann

[Dario Cazzola]

Hi Yoann,

Usually you get this kind of error when muscles cannot generated the force needed to accelerate/decelerate specific bodies as requested in the IK input.

Another problem might be related to the difference between SIMM (DELFT model has a SIMM structure?) and OpenSim in terms of muscle-tendon paths implementation. I'd suggest to have a look and use to the recently Upper Extremity Dynamic Model project: https://simtk.org/projects/upexdyn.

If you are also interested in neck muscles and a simpler scapuloclavicular joint representation (no intermediate masses bodies) you can have a look to MASI model: https://simtk.org/frs/?group_id=982

Cheers

Dario

[yoann blache]

Dear dario

Thank you for your reply.

I am going to take a look into the upper extremity dymanic model.

Cheers

Yoann