The difference between SO and CMC

[H V]

Hello,

I am learning to use OpenSim.When I read the materials,I find that both Static Optimization and CMC can output the muscle forces.But when I look over the example Arm 26 provided in Models ,I found the results from arm26_Actuation_force.sto and the results from arm26_StaticOptimization_force.sto has a big difference.
For example ,at the time 0.1 s ,the force of TRIlong from SO is 0.015 while 35.32 from CMC.
I am confused of this ,did I miss something or misunderstand something ?


PS. I find that the muscle force results of SO usually begins with a very little number like zero, while the muscle force results begins with a big number,and how to deal with the results of CMC ?

Hope someone can help me.

Thank You,

WANG

[Brandon Brown]

Hello,

The difference in what you're seeing is that cmc accounts for both passive muscle forces and active muscle forces. To understand the difference between the two, read the opensim pages on muscle theory. Static optimization only accounts for active forces in the model while cmc accounts for both passive and active forces.

Go to this page: http://simtk-confluence.stanford.edu:80 ... blications

It takes you to links on the muscle theory.

Brandon

[H V]

Hi Brandon
Thank you for your answer,I'll go to learn that.

By the way , I have seen one of your topic about the SO.I am using the same upper extremity dynamic model as yours.And now I have a problem,that is ,I want to add the external load ,OpenSim crash.

Or when I tried this in the CMC ,with the Actuators and External loads ,but the results make no difference . So I'm confused about this ,I'm wandering the file Actuators.xml and the force.xml has some mistakes.

Can you tell me how did you set the file when you added the external forces using the upper extremity dynamic model .

Thank you again for your help,
WANG

[Brandon Brown]

Hello Wang,

I actually didn't use any external loads in my model so I'm not sure what would cause your model to crash. Make sure you have a reserve actuator for every joint. Set the control values to positive and negative infinity and set the optimal forces to 1 for each reserve. If there is a joint which doesn't have a reserve, the external loads could be imposing too much on your model such that a solution cannot be found.

Brandon

[H V]

Hi Brandon

Thank you for your answer,I had already made a reserve actuator for every joint,while this time the CMC tool directly can not run.Maybe I had misunderstood or lost something ,I 'll go to see the files and check it again.

Thank you again for your help.

WANG