Changes in JRF with different cmc time windows

[Amanda Vinson]

Hi there,

Utilizing a smaller cmc time window (0.001 compared to 0.005) is impacting the calculation of the joint reaction forces from those cmc results. When I keep every input file and parameter the same and run CMC with the 0.005 time window and then repeat it with the 0.001 time window, I see an increase in the vertical knee JRF. My understanding is that the cmc time window should only be affecting the "smoothness" of the results rather than resulting in changes in data results and representation.

Can you provide insight on why this difference is occurring? Is there reason to believe one time window result over the other?

I have attached figures demonstrating the difference.

Thank you.

[Carmichael Ong]

With CMC, muscle excitations (and consequently forces) can differ based on the CMC time window. It's possible that differences in these muscle forces account for the differences in the knee JRF, and you could check if muscles that cross the knee have higher forces in the simulation with higher knee JRF.

There are different ways to validate a simulation, for instance, one of which is if you had collected EMG data with which you can compare the CMC solution. More detailed info on validation can be found in this paper: https://nmbl.stanford.edu/publications/ ... ks2015.pdf