simtk.org

Dear all, I am now working on the simplified version of ULB model. I use the simulation data from this project in SimTK

https://simtk.org/frs/?group_id=899

. The model goes well on IK,ID,RRA, but failed in CMC. I always got the error below:

Exception:
Model::equilibrateMuscles() Unable to compute equilibrium for this muscle.
Please verify that the initial activation is valid and that the length of
the musculotendon actuator doesn't produce a pennation angle of 90 degrees
or a negative fiber length.
Solver for force-velocity multiplier failed to converge.
In Object 'glut_med1_r' of type Thelen2003Muscle.
Thrown at thelen2003muscle.cpp:1704 in calcfvInv().
In Object 'glut_med1_r' of type Thelen2003Muscle.
Thrown at thelen2003muscle.cpp:350 in computeInitialFiberEquilibrium().
file= c:\projects\opensim-build-releases\opensim-core\opensim\simulation\model\model.cpp
line= 1193

Since I have already checked the properties of muscle glut_med1_r and it seems to be normal.
Can anyone tell me how should I do to solve this problem? Thank you.

The exception message indicates that no solution can be found in which the muscle and tendon are in equilibrium. During initialization, the algorithm may be using the default_fiber_length and default_activation properties as initial guesses. As suggested by the exception message, you could try adjusting these properties. You might also try starting the simulation at a different time point to determine whether there might be a more general issue.

Thanks a lot, Thomas. I'll try your suggestions to see if the result improve.