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imihasan / rmr-solver

Repository storing MATLAB scripts to estimate activations of shoulder muscles using the Rapid Muscle Redundancy (RMR) solver.
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Check if the CoMs are in the correct place #7

Open itbellix opened 9 months ago

itbellix commented 9 months ago

Hi @imihasan, and happy new year!

I am checking now where the CoM of the various bones in Ajay's model are, as I remember that from our last meeting we concluded that they came from one dataset, while the geometries used came from another. It looks to me that the center of masses (and consequentially also the inertias) might be a bit off. Probably not too much, otherwise the model would have never worked in the first place, but maybe something to discuss in the next meeting as well?

Here you can see the image depicting where the CoMs are (I obtained it in OpenSimCreator, which offers a convenient functionality to visualize their location):

imihasan commented 9 months ago

Hi @itbellix , welcome back!!

Thanks for pointing that out! I think the CoMs should be alright. Typically in anthropometric datasets the inertial properties are properties of the body segments considering bones, muscles, skin and other soft tissues around. If you look at the humerus you notice that the CoM is a bit off the bone geometry. That's because biceps and surrounding muscles are considered in the computations. I will double check all the inertial properties after finishing elbow muscles and moment arms. I will keep the issue open until then.

For now I have a question on that point. Do you think inertial properties of the thorax would affect the muscle redundancy solution? When we find induced accelerations, distal segments have effect, but muscles in the same time attach on the thorax. What do you think? I set the mass of the thorax to a very big number and it had a minor change I believe. You may try that and let me know what you think.

itbellix commented 9 months ago

Hey @imihasan, thanks for double-checking. I agree with you that the position of the CoMs appears reasonable, I was indeed forgetting that the soft tissues are also accounted for in their computation!

For what concerns the inertial properties of the thorax, I would expect that they would not matter when the thorax movement is completely replicated through coordinate actuators. I do not think that the muscle attached to the thorax would be influenced by the thorax' inertial parameters, the only thing that matters should be the correct pose of the thorax itself (which will determine the muscle parameters to be considered, such as muscle-tendon length, direction of the force exerted, and so on). So, I think that the changes in muscle activation that you observe are an indirect effect: as the optimization scenario changes to accommodate for the new inertial properties of the system, this has a sort of "spill-over" to the muscle activations as well, as the minimum found is not the same one as before. The changes should however be very small, if my reasoning is correct.

Does this make sense?

imihasan commented 9 months ago

Hi @itbellix ,

I think it makes sense. Thanks for clarifying this!