IAA invalid results for rolling on surface Constraint

[Amy Hegarty]

I am trying to use the IAA tool with the rolling on surface constraint, but my output data is giving me some unrealistic results. In the middle of single limb stance the muscle contributions to the propulsion/braking acceleration (x-dir) of the center of mass become zero for all muscles. I am not having that issue with the vertical component though. I have tried to run the same analysis using point constraints and weld constraints, which does produce non zero values for the entire stance phase, but the values do not seem reasonable. Has anyone experienced this same issue, or have any suggestions on what could be the cause?

[Laura Martin]

Hi,

I am facing a similar problem. I have performed IK, RRA and CMC for a sprint start. When I use those results and run IAA, constraints forces with a RollingOnTheSurface model do not totally follow GRF. Indeed, there is a sudden drop to zero of components X and Z, and at that time also the Y-component ceases to follow the trend of GRF_Y:

Forum_IAA.png (35.33 KiB) Viewed 158 times

After checking the rolling constraint model in
https://www.ncbi.nlm.nih.gov/pmc/articl ... 469166.pdf, I noticed that there is a small drop in the X direction of the reaction force applied to the ground:

Forum_RollConstraint.png (22.1 KiB) Viewed 158 times

Therefore, I was wondering if the drop is due to the model itself (my stance phase lasts 200 ms, that why data starts at 14% of the cycle due to the needed 30 ms in CMC, so maybe the drop is more noticeable here as well) or due to previous calculations.

Thanks in advance!

Best,

Laura