Joint Reaction Force Spikes

[Maxine Olson]

Hi Everyone,

I have an issue that I haven't been able to find on the forum. I am running a joint reaction force analysis. I have a custom multi-segment foot model. I have run IK, RRA, and static opt. I am using those outputs along with multiple GRF vectors as input for the joint reaction analysis. My output of the joint reaction analysis has several cells time points that are -nan and others that are spiking to the E280 magnitude. Has anyone encountered this before.

I have checked all the input files and they are reasonable smooth curves. I have filtered the IK data when running the RRA. When I run inverse dynamics the output looks reasonable.

Any ideas?

[Jon Stingel]

Hi Maxine,

It might be helpful to know more about your problem setup, for example what joints you are seeing the spiking at and what changes to the foot model you have implemented.

Additionally, since your inverse pipeline seems to be working it is likely not this, but have you ensured that your GRF file does not contain any NaNs in the forces or the center of pressure locations?

Hope this is helpful!
Jon

[Maxine Olson]

Thank you Jon. I'm using a multi-segment foot. I see the spikes, x E280 and -nan, at the ankle and knee joint during normal gait.

I started with the KU Leuven foot model. I have 1 degree of freedom at the ankle, and I have altered the model to include 2 DoF at the subtalar joint, 3 degrees of freedom at the Chopart joint, a weld joint at the Lisfranc joint, and 3 DoF at the MTP joint. Additionally and uniquely, I have applied separate GRF vectors to the hindfoot and forefoot segments.

RRA and Static Opt run fine. Inverse dynamics runs fine and results are as expected for ankle and chopart joint moment. But in the joint reaction calculation at random time points equation are not converging.

I don't know if anyone has seen this before? I have checked all of my inputs for NaN and/or unexpected values and I can't find an issue.

Thank you!