Different results for the same subject and C3D file!_AMMR 2.1.1 (AnyBody 7.1) vs. AMMR 2.4.2 (AnyBody 7.4)

Why are the attached results of the Left_Hip_MediolateralForce different for the following two versions:
-AMMR 2.1.1 (model solved on AnyBody 7.1)
-AMMR 2.4.2 (model solved on AnyBody 7.4)

The same generic subject anthropometric data and GaitNormal_1 C3D file.
Solved for FirstFrame = 218 (LHS) to LastFrame 335 (LHS).

Hi Ahmed

I can't tell you the exact reason the difference. I would like to look into the details of it when I get back from summer holiday if you remind me again.

I suspect a number of things are different between the two versions of the model repository. The most likely reason is that the marker protocol of the example has changed. MoCap based musculoskeletal models are very sensitive to marker positions. This unfortunate but consequence of physics and kinematics. When for example the ground reaction force vector passes very close to the hip joint center, then only small differences (~0.5 cm) could cause the moment arm and forces to change drastically.

An other reason for such a difference could be improvements to the model and muscle geometry. Especially, the muscle wrapping has been improved several times during the last 3-4 years.

You can find a list of all changes to the model in the changelog:

Changelog — AMMR v2.4.1-beta Documentation (anyscript.org)

It is not easy to get an overview of all the changes in the changelog. The two versions you are referencing span a period of 3-4 years.

Alternatively, you can join our GitHub development repository. There it is possible to see all changes to the model and files in detail.

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