static optimization for UE model

[Nithin Kurup]

Hi,

I am trying to perform static optimization on the MOBl_upper extremity model for the elbow flexion motion. I am using and comparing the results with respect to arm26 sample. I am using the marker data for elbow flexion from arm26 and using it on the mobl model.

In the mobl model- I fixed the translational and rotational degrees of freedom of the thorax, removed the coordinate limiting forces, and updated the model to thelen2003. The static optimization works after adding the reserve forces for the model. No RRA was performed.

the issue is the muscle biceps is not producing enough force in range of 1-2 N, as I compared it with the arm26 results is 120 N. I tried to reduce the optimal force from 100 to 50N in the reserve coordinate force file, the value of force didnt increase rather it started to get noisy/ zig zag pattern.

How can I fix this issue. thanks

Nithin

[Thomas Uchida]

The MoBL model contains many more elbow flexors than the arm26 model. The flexion moment generated by BIClong in the arm26 model is likely distributed among several muscles in the MoBL model. See the "How Static Optimization Works" page on Confluence (http://simtk-confluence.stanford.edu:80 ... tion+Works).

[Nithin Kurup]

Thank you for your kind reply.

Unfortunately both the models have the same number of muscles (reduced the number of muscles of MOBL model). Will check again , why the force is not building up. Thanks again.

Nithin

[Nithin Kurup]

Thank you for your help. I solved my issue.

Just have a small doubt regarding the reserve actuator force. I tried to add a reserve force of 1 N in one simulation and 50 N in another simulation for the coordinates and measured the forces produced by the biceps. Noted that in 1N- the biceps peak force is around 450 N and for 50 N its around 45 N. Assuming the higher the reserve force, the less muscles are used -resulting in lesser force.

In such cases how do we set the optimal force for the reserve actuators? so that the value can be almost in the real range, as I dont know which is the real value.

thanks again.

Nithin

[Thomas Uchida]

how do we set the optimal force for the reserve actuators?

Reserve actuators should be configured so that they are recruited only when the muscles are incapable of generating the necessary joint moments. When validating your simulations, you should ensure that the reserve actuator torques are relatively low (e.g., see the guidelines for CMC at the bottom of the "Getting Started with CMC" page in the Confluence documentation: http://simtk-confluence.stanford.edu:80 ... d+with+CMC). Also see the following page (the first result when searching for "reserves" in the documentation): http://simtk-confluence.stanford.edu:80 ... +residuals.