CMC with JRA

[pauline neerpelt]

Hello everyone,

I'm reaching out for some guidance on utilizing Computed Muscle Control (CMC) and Joint Reaction Analysis (JRA) to assess the resultant force acting on the proximal row and radius during a maximum grip strength exercise.

I came across a tutorial where forward dynamics (FD) was employed to determine grip force on a dynamometer (ARMS simulation tutorial: module 3). However, I'm interested in reversing this methodology as I have data available for the maximum grip force exerted.
In the tutorial, the OpenSim model utilized includes the following features:

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An elastic foundation contact was integrated between a massless dynamometer cylinder and massless cylinders overlaying the phalanges. The dynamometer cylinder is securely fixed via a weld joint to the third metacarpal bone. In the tutorial, the resultant force acting on the third metacarpal (in the y and z-directions) at this joint is defined as the grip force.

For my CMC analysis, I used the following settings:
- Desired kinematics: States file sourced from the FD output.
- Tracking tasks and actuators (as low as possible) for all unlocked joints within the model.
- Control constraints applied to all muscles.
- External loads incorporated using the JRA output from the FD tutorial.
These settings were based on the JRA configurations specified in the FD tool, where the parent of the GripForceJoint is identified as the third metacarpal.

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However, upon comparing the control and force files from the FD tutorial with those obtained from the CMC simulation, I noticed significant differences. This prompts me to question whether I have used the correct methods and whether it's expected for results to deviate due to the inclusion of reserve actuators.

Any insights or guidance on this matter would be greatly appreciated.