Antagonistic co-contraction in CMC?

[Brody Hicks]

Hello,

I have some data for a fairly deep squat that I am trying to simulate using the Catelli model by performing RRA followed by CMC. With RRA, I am able to get my residuals, rotational errors, and translational errors within the recommended values for walking and running, so I have moved on to CMC to examine muscle force/activation. However, I am noticing some weird behavior in the muscle activation of the quadricep and hamstring muscle groups (particularly in recfem and bflh).

First of all, the recfem, glmax3, bflh, and vaslat all achieve maximum activation at some point during the squatting motion. I could understand the quadricep and gluteus maximus muscles maxing out if the model was not sufficiently strong, but it seems strange to me that the bflh is maximizing since the hamstrings aren't the primary muscle group utilized in a squat. I noticed the published muscle activations in the Catelli paper also have high activation levels for the bflh muscle, but I am curious if anyone else finds this strange?

Furthermore - if I increase the strength of the model 10x, the recfem and bflh still achieve maximum activation (see figure). It's as if these muscle groups are "fighting" each other. This seems to be true if I run a muscle analysis on the results and plot each individual muscle's contributions to the joint moment (i.e. the recfem generating a large hip flexion moment and the bflh generating a large knee flexion moment, thus counteracting the muscles trying to generate respective extension moments). However, I'm unsure what's causing this problem or how to fix it.

Please let me know if anyone has any thoughts. I'm happy to append some supplemental data if that would provide clarification.

Best,
Brody