Different left and right side muscle activations

[Rahid Zaman]

Hello,

I am trying to find muscle activations using Static optimization tool in OpenSim for a symmetric lifting motion. The kinematics and GRFs are generated from a software, and they are same for both left and right sides.

When I am using the Full body lumbar spine model (https://simtk.org/projects/fullbodylumbar), the muscle activations for the same muscles on right and left side are different. I am using this model in OpenSim 4.1 by converting it, as this model was generated using OpenSim 3.2. I run the Static optimization in OpenSim 3.2 also to verify the results. The muscle activations on both sides are different for OpenSim 3.2 also.

On the other hand, when I am using another full body model developed by Dr. Rajagopal (https://simtk.org/projects/full_body/), the muscle activations for same muscle on both sides are similar.

As the input kinematics and GRFs are same, I was expecting the muscle activations on both side will also be similar. The additional actuator values are also same for both side. As far as I have check, the maximum isometric force, Optimal fiber length etc. are also same for both sides muscles.

Can anybody help me to understand why for one model, muscle activations on both side are similar and for another model it is different?

Thanks.

[Carmichael Ong]

Have you also checked that the muscle paths are symmetric for the fullbodylumbar model too? It's often easy to miss these small errors since they usually have small effects that are hard to find for motions such as walking.

[Rahid Zaman]

Thank you for your response.
I think you are right. This may be the source of dissimilarity. For some muscles, the left and right side GeometryPath are not symmetric.
Do you think, it should be same?

Thanks.