Joint Reaction Analysis

Provide easy-to-use, extensible software for modeling, simulating, controlling, and analyzing the neuromusculoskeletal system.
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Gil Serrancolí
Posts: 9
Joined: Thu Mar 17, 2011 1:37 am

Joint Reaction Analysis

Post by Gil Serrancolí » Mon Feb 04, 2013 2:36 pm

Hello,

I would like to obtain the joint reactions of my model during human gait. I am running the JointReaction Analysis but I obtain forces and moments that are far away from the inverse dynamic loads.

I have a model of one leg (pelvis, femur, patella, tibia, talus, calcaneus and toes). I use the Analyze Tool using as inputs:

- Motion from file (the Inverse kinematics results) / Filter coordinates (6 Hz)
- Actuator and External Loads --> External Loads --> External loads spec. file (the same .xml file that I used for the inverse dynamics analysis).
- Analyses, JointReaction: Joint Names (all), Apply on bodies (child), express in frame (child).

As far as I understand, the reaction loads are those that are necessary to produce the prescribed motion. For a DOF like the knee flexion I think that the Reaction Loads should be the same that the calculated by Inverse Dynamics. But I obtain a flexion moment that is completely different both in magnitude and shape. Using inverse Dynamics Analysis, it seems reasonable, but using Joint Reaction Analysis it doesn't.

I also tried running JointReaction Analysis and Inverse Dynamics Analysis using a simpler model (the Arm26 model). The inverse dynamics loads seem reasonable but the Joint Reaction loads are completely different.

What am I doing wrong?

Thank you very much in advance,

Gil Serrancolí
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Ayman Habib
Posts: 2236
Joined: Fri Apr 01, 2005 12:24 pm

Re: Joint Reaction Analysis

Post by Ayman Habib » Tue Feb 05, 2013 11:01 am

Hi Gil,

Please consult the documentation page below for what to expect from InverseDynamics and from JointReaction analysis and let me know if you continue to have questions.

http://simtk-confluence.stanford.edu:80 ... seDynamics

Best regards,
-Ayman
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Gil Serrancolí
Posts: 9
Joined: Thu Mar 17, 2011 1:37 am

Re: Joint Reaction Analysis

Post by Gil Serrancolí » Wed Feb 06, 2013 8:58 am

Thanks Ayman,

I had muscles in my model and I needed the joint reaction forces using just the skeleton, so when I run JointReaction Analysis with no muscles, what I obtained makes sense. It seems they actuated passively.

I also ran it using a simple pendulum and I could understand the difference with JointReaction Analysis and Inverse Dynamics.

Thank you very much,

Gil
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