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Hello,

I am currently estimating joint reaction forces at the hip, knee and ankle using the Opensim Joint Reaction Analysis tool for a model with a transtibial amputation.

When running the tool with validated static optimisation results, and all lower limb muscles defined in the model (all muscles over prosthesis are disabled) I obtain the following results at the intact limb knee (pictured as resultant force).
After completely removing the muscles covering the prosthesis from the model I obtained this result.
I was wondering why there is such a large disparity in results when all I am changing is whether the muscles are disabled or removed from the model all together? Additionally, below is the relevant results for the prosthesis limb knee. As you can see the same issue presents for muscles attached to the model (disabled muscles) however, the results for when the muscles are completely removed appear more as to what I would expect.
Below is my setup for the analyze tool
Any assistance on fixing this issue when calculating joint reaction analysis as well as how to improve the quality of my results (particularly for the intact limb) is highly appreciated! I can provide the model and all relevant files if required.