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Hello,

I want to get a better understanding of how the joint reaction analysis is performed, for example in the L5_S1_IVDjnt_on_lumbar5_ground_fy.

I think the joint reaction analysis is performed using the following formula: R(L5_S1) = inertial load - (Fexternal + Fmuscles + Fcontraints + R(L4_L5_IVDjnt_on_lumbar5_ground_fy). Can you tell me if this is correct?

I want to know which Fmuscles are applied on lumbar5 to get the joint reaction force. Can you tell if it this is possible and how to do this?
I am performing the flexion motion given in the tutorial without adding extra external forces.

Thanks,
Karlijn

https://simtk-confluence.stanford.edu:8 ... s+Analysis
I can't explain it any better than the OpenSim documentation. But in general, it appears that you have the correct idea. The JRA considers all the forces (when solved for) and then finds the one unknown of the joint.

As for getting info about specific muscles etc. You can use some of the muscle analysis tools to find which muscles cross a given joint or write an API.
For another model/project, I have some sample code that will give you a good foundation for an API in Matlab.
https://simtk.org/projects/emg_opt_tool.

Hopefully this helps.
Jake Banks

Thanks for the reply!
I will have a look at the muscle analysis.

Karlijn Spijker