I am using AnyBody 7.3 and the full-body model from AMMR. I am working on analyzing the compression and shear forces of the L5S1 disc. I know that I can find these forces in Main.HumanModel.BodyModel.SelectedOutput.Trunk.JointReactionForce, but my question is that according to what coordinate system are these components calculated? Is it the sacrum segment or sacrum endplate or somewhere else?
The coordinate systems in SelectedOutput.Trunk.JointReactionForce depends on the joint that you are interested in. Each is expressed in the local coordinate system of the joint. You can find the joint definitions in the model tree in HumanModel.BodyModel.Trunk.JointsLumbar or in the JointsLumbar.any file.
The joint is made up of two reference frames, and the joint reaction forces are expressed in the coordinate system of the first reference frame inserted in the joint definition. If you look at JointsLumbar.any file, that will typically be the reference node on the proximal segment in the joint.
Hope this helps.
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