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Hi everyone,

I am using Opensim to build a fully functional arm. I am almost done with it.
My work requires me to analyse the movement of the arm with various lengths.
So, throughout my project, i have to repeatedly change my humerus, radius and ulna length. I am doing this by changing the scale value of each of the body.
But, every time i change the length of any of this bone, the muscle attached to the bone goes completely away from where it was originally positioned.
I have attached an image(orginal.png) of my original model with just one muscle(Triceps) wihtout changing any length.
Yokhesh I have attached the image(humerus_length_change.png) of the same model with the same muscle once i have adjusted the length of the humerus bone. There is a pretty big change in the muscle position. Is there a way to make the muscle automatically adapt to the bone's size? Or do i have adjust the path point of the muscle manually every time i change the bone length?
Please let me know.

Regards,
Yokhesh

Hi everyone,

I encountered a problem related to muscle location or path when I change the length or scale of the body/bone in the simulation.
I have posted the relevant details for the error along with a couple of images.
Could anyone please take a look at it and let me know any possible solution?
Any suggestions would be appreciated.
I badly need it for my research. Please let me know.

Thank you,
Yokhesh

So, throughout my project, i have to repeatedly change my humerus, radius and ulna length. I am doing this by changing the scale value of each of the body.

How exactly are you doing this? Are you running the scale tool each time or are you directly editing some part of the .osim file? If you are doing the later (editing the file), then you aren't updating the location of the muscle points in the humerus frame. The Scaletool doesn't just scale the length of the bodies, it also adjust all muscle points such that they are in the same relative location of the parent frame.

Hi,

I am actually directly editing the scale value in the .osim file and not using the scale tool.
So, the only way to make the muscle points automatically adapt itself is by using the scale tool along with the marker data?
Or is there a way to do the same by just updating the scale value in .osim file because I do not have the marker values from the subjects?

Regards,
Yokhesh

You don't have to use markers for the scale tool-- you can apply manual scale factors to each body.

Hi James,

Thank you so much for sharing the info.
That worked!!!
I was able to scale the body without the muscle moving away from its path..
Thank you..

Regards,
Yokhesh