Muscle Weightage in CMC

[Shivangi Giri]

Hello,
I wanted to know if there is a way to add weightage to muscles before performing CMC, like the way we add weights for joints.
I tried adding a task for the said muscles in the CMC task file with weights but the output generated did not show any effect of weights on the activation pattern of the targeted muscles.

Regards,
Shivangi

[Carmichael Ong]

Unfortunately you cannot change the weights corresponding to different muscle excitations/activations in CMC or static optimization provided by OpenSim.

A number of community projects have written their own static optimization routines to have this flexibility.

[Thomas Uchida]

The CMC optimizer is minimizing the sum of squared muscle activations, so (if you're adventurous!) you could try changing the maximum isometric forces of the muscles to adjust the relative cost of recruiting a particular muscle---keeping in mind that activation cannot exceed 1. The active part of the muscle force will just scale up/down (e.g., if the maximum isometric force of a muscle is doubled, you will require only half the activation to generate the same active force); however, this change would also affect the passive force. One way around that could be to duplicate every muscle in the model; one copy generates only the passive force (by constraining its activation to zero) and the other copy generates only the active force (by zeroing its passive force--length curve). Just an idea... I don't know whether it would work in practice.

[Shivangi Giri]

Thank you Carmichael and Thomas for your replies.
I will try your suggestion Thomas and would let you know how it goes.

Regards,
Shivangi