Simulating co-contraction by extending the recruitment criteria

Hi guys,

More and more researchers think that antagonist co-contraction must be accounted for in musculoskeletal models in order for these models to be closer to reality. I recently found an interesting paper that you might know:

Forster et al. (2004) Extension of a state-of-the-art optimization criterion to predict co-contraction, J. Biomech 37, 577-581

They use a shift parameter “xs” in the optimization function to create some co-contraction.

Do you think that this would improve the concordance between AnyBody forces estimations and experimental data ?

I think that adding this parameter in AnyBody would be easy and fast, but I’m not sure that I can do it easily.

Thank you.


Hi P.-O.

In AnyBody you can actually specify lower as well as upper limits on muscle recruitment. A lower limit will require a certain basic tonus in all the muscles. Currently, this is all you can do in terms of specifying co-contraction.

Best regards,

Hi John,

Ok. I should have a look at these bounds.

In my researches, I found that the AnyBody intact shoulder model can predict co-contraction as a recruitment strategy to respect the glenohumeral stability constraint. This seems concordant with the joint stabilizing role of co-contraction. Do you think that the actual stability constraint on the gleno-humeral resultant force is sufficient to predict a realistic amount of co-contraction ?

The paper of Nikooyan et al. (2012) An EMG-driven musculoskeletal model of the shoulder is about adding a co-contraction activity based on EMG measurement in a shoulder model to improve the similarity between their model estimations and in-vivo joint data of Bergmann. My opinion is that that these in-vivo data do not represent the intact joint, since the presence of the prosthesis is likely to increase the sensitivity of the joint to instability and friction. Thus, the measured co-contraction would rather be related to the presence of a newly inserted prosthesis.

What is your opinion ?