Re: Extract Muscle Force Vectors (Lines of action)
Posted: Fri Mar 27, 2015 7:42 pm
Hi all,
I'm bumping this old thread because I have a related question.
I've previously used OpenSim to calculate muscle line-of-action (LOI) vectors using the method Ton described earlier in this thread (define translational coordinates at the joints, then ask OpenSim to calculate "moment arms" with respect to these coordinates; partial derivatives of muscle lengths with respect to the coordinates in question gives LOI vectors in the "child" segment's reference frame). This works great if your goal (for example) is to calculate hip joint contact forces and you need to know LOI vectors for all muscles that span the hip, in the femur reference frame.
What I'm trying to do right now is a bit different. I would like to calculate LOI vectors in the femur frame for all muscles that attach anywhere on the femur. I haven't been able to get the method described above to work for this. It misses out on the LOI vectors for muscles that originate on the femur (vasti, gastrocs) because their lengths are not affected by hip translation (shank and patella stay put because their parent is the femur).
The force directions plugin that Ayman mentioned earlier sounds like it would do what I'm looking for, but unfortunately it does not run in OpenSim 3.2.
Is there another way of accomplishing this within the <body> and <joint> definitions in a .osim file? The only other approach I could think of was to manually extract all the relevant muscle coordinates, wrapping definitions, and reference frames and do it in Matlab, which I was hoping to avoid =)
Ross
I'm bumping this old thread because I have a related question.
I've previously used OpenSim to calculate muscle line-of-action (LOI) vectors using the method Ton described earlier in this thread (define translational coordinates at the joints, then ask OpenSim to calculate "moment arms" with respect to these coordinates; partial derivatives of muscle lengths with respect to the coordinates in question gives LOI vectors in the "child" segment's reference frame). This works great if your goal (for example) is to calculate hip joint contact forces and you need to know LOI vectors for all muscles that span the hip, in the femur reference frame.
What I'm trying to do right now is a bit different. I would like to calculate LOI vectors in the femur frame for all muscles that attach anywhere on the femur. I haven't been able to get the method described above to work for this. It misses out on the LOI vectors for muscles that originate on the femur (vasti, gastrocs) because their lengths are not affected by hip translation (shank and patella stay put because their parent is the femur).
The force directions plugin that Ayman mentioned earlier sounds like it would do what I'm looking for, but unfortunately it does not run in OpenSim 3.2.
Is there another way of accomplishing this within the <body> and <joint> definitions in a .osim file? The only other approach I could think of was to manually extract all the relevant muscle coordinates, wrapping definitions, and reference frames and do it in Matlab, which I was hoping to avoid =)
Ross