Magnitude of Joint Reaction Force Does Not Make Sense Based on Static Optimization Results

[Luke Mattar]

Hello,

I have been developing a model for the glenohumeral joint where the end goal is to investigate changes in the magnitude and direction of the joint reaction force during abduction. I believe I am getting reasonable results for static optimization. However, based on the muscle forces from static optimization I do not believe the results I am getting from the Joint Reaction Analysis makes sense.

Given Figure 1, I would expect the magnitude of the joint reaction force to also increase and then start decreasing around 50s. However, the joint reaction force just decreases almost linearly throughout abduction (Figure 2). I have watched multiple videos regarding proper set up of the Analyze tool but can't figure out what is wrong.

I would greatly appreciate any advice or feedback anyone may have, and will be happy to provide more information if needed. Thank you in advance for your time!

[Luke Mattar]

Hello all,

Just in case anyone looks at this post in the future, I figured out the solution.

I had two muscle actuators and 2 coordinate actuators that were "disabled" in the gui as I did not want to include them in the analyses. Since they were disabled, there were obviously no results for them in the SO forces file. However, Joint Reaction Analysis did not like this and an error popped up saying "the force file did not contain enough actuators".

I removed the disabled actuators from the .osim file, re-ran my workflow and the results of the Joint Reaction Analysis makes sense.

Hope this helps someone in the future!

Kind regards,
Luke