Muscle Activation

[Ayman Habib]

Hi Themis,

For reporting changes in MT-length, please file a feature request and we'll try to accommodate it or provide a mechanism to obtain it. For now you'll have to compute it manually outside OpenSim. You can also write your own analysis to compute and report these quantities (MT-length changes, relative to what exactly?).

I'm not sure how your partner produced the files he/she passed on to you but it sounds like these were files exported from the plotter. You can get the same output with arbitrary granularity/range using the MuscleAnalysis and the AnalyzeTool.

Hope this helps and please let me know if you have further questions or need more details regarding how to run the AnalyzeTool with MuscleAnalysis.

Best regards,
-Ayman

[Themis Toumanidou]

Hi Ayman,

I think I didn't explain the case very well in my previous post and therefore I attach the files I am referring to in order to make it clearer.I am a beginner in inverse dynamics analysis and OpenSim and probably this justifies the problems I face.

My partner is working with the Lumbar_C_238 model (Christophy et al.2011) of the lumbar spine and performed an inverse dynamics+static optimization analysis to predict the muscle forces using the motion files that were also available on the project page (he did a first analysis for a 40d flexion (MotionFile_C_40DegrFlex). So, he passed me, e.g. for the psoas major, a file with the force estimations (Psoas.txt-please see attached) and another one with the MT length (PsoasMT.txt-please see attached) per fascicle for each increment of the time history.

I wanted to produce the σ-ε curves and that's where I found out that this analysis could not give me the MT length changes.So, as you said, I tried to compute it manually outside OpenSim. However, as you can see in the MT file, it is not clear for me at each increment of the time history to which degree of the flexion analysis it corresponds. I mean, the 2nd column is ranging between -70 and 26 so I interpret that this does not refer to the degrees of inclination because I would expect a range between 0 to 40. Apart from the fact that, as you can see, the psoas fascicles are constantly lengthening and therefore cannot correspond to a flexion test but to an extension (I conclude to this because the rest of the local muscles of the back were similarly shortening).

I don't know if I misunderstand the results but it would be really helpful for me if you could give a clue for that.In the meantime,I start exploring the MuscleAnalysis and AnalyzeTool.

Thank you for your help!

Best Regards,
Themis