From joint torque to muscle activation

[Ignacio Abadía]

Hi,
I am a new OpenSim user and I was wondering if it is possible to translate from a joint torque value to the corresponding muscles activation values.

To be more specific: I am using the arm26 model and developing a controller able to learn the joint torque values required to perform a specified movement (i.e., an elbow flexion/extension previously computed using Inverse Kinematics). At every time step the controller provides a joint torque to achieve a desired joint state (position and velocity), and I need to translate that joint torque to muscle activation of the muscles involved in the movement. Is there a way to achieve this translation?

Thanks in advance,
Ignacio

[Thomas Uchida]

The Static Optimization and Computed Muscle Control tools do this. A good place to start might be the "Overview of OpenSim Workflows" page in the Confluence documentation: https://simtk-confluence.stanford.edu/d ... +Workflows.

[Ignacio Abadía]

Hi Thomas,

Thanks a lot for your reply. I took a look at the Static Optimization tool and I will apply the "constrained by force-length-velocity properties" equation to solve for the muscle activation from a given joint torque at each time step https://simtk-confluence.stanford.edu/d ... tion+Works.
I just have one question regarding that equation (forgive my ignorance on the topic): what's the meaning of f(F0m,lm,vm) i.e., "force-length-velocity surface"? Is it a constant or varying property of the muscle? How could I compute its value?

Thanks,
Ignacio

[Thomas Uchida]

Please see the papers on the "Muscle Model Theory and Publications" page in the Confluence documentation: https://simtk-confluence.stanford.edu:8 ... blications.