simtk.org

Hi all,

I understand the aim of this project is to provide a detailed model of the thoracolumbar spine and rib cage, however it is described as a full-body body including upper extremities based on the Upper Extremity model from Holzbaur et al. (2005), which leaves me wondering if there is any reason as to why the arm muscles are not present on the model file?

I am currently developing an application that requires a complete upper/full body model (include thoracic, arm/hand and neck muscles) and struggling to find a model that fits these requirements, which forces me to assemble my own model based on this project and the Upper Extremity model. However, I've noticed that the body structure is slightly different on the latter, e.g. with additional "phantom" bodies "humphant" and "clavphant" so my question is - are they compatible in the sense that one can just add the missing bodies and muscles to the full body model file, or is any kind of previous processing and/or scaling required?

Thanks in advance for any help or input you provide,

Joao,
I'll try to answer your questions, but I may need to get back to you on 1-2 items (I'm a fairly new postdoc to the lab/project, and was not around when they assembled the full-body model).
1- my understanding on excluding the arm muscles was/is that they do not play a major role in estimating thoracolumbar demands. Replacing muscles with torque actuators allows the sims to solve more easily etc.
2 - So, could you just add the muscles?... yes. The model has been scaled slightly (I believe) so you may want to compare segment lengths and adjust attachment points accordingly. Up to you what to do with muscle Fmax's (in my experience, always air on the side of making things stronger, while keeping the Fmax proportions between muscles).
3 - I am not familiar with these 'phantom' bodies, I assume they must be in the Holzbaur model. As with comment #2, you can most likely add them, but may need to modify their scaling and location slightly to meet the current full-body model (or scale the full-body model... "vice versa").

I'll ask the group some of these questions later today, to confirm my suspicion's. If anything should differ, I'll get back to you.
Jake Banks

Thanks for the answer.

Yes, the Holzbaur model includes several intermediary 'phantom' null-mass bodies without any geometry: 'clavphant' between the clavicle and the scapula, 'scapphant'/'humphantX' between the scapula and the humerus. Additionally, contrary to the 'sernX_clavX_jnt' and 'clavX_scapX_jnt' joints in this full body model, they are not WeldJoints but rather CustomJoints which allow 5 DoF/Coordinates between clavicle and scapula, and similar between scapular and humerus bodies, hence my question as to how compatible can they be.

At this stage, I'm not particularly worried in the strength scaling as we plan to implement our own subject-specific strength scaling procedure from experimental data, but dimensional/mass seems relevant in order for the resulting reference model to be consistent.