Center of Mass Interpretation

[Krish Narotam]

Hi,

I am working on looking at center of mass data for prosthetics patients.

We are not sure how to interpret the data, but one of my issues with the data.

I am not sure how it works in the back end. But the data should make sense across, the position graph's slope seems to not line up with the velocity graph. The position data is a seeming constant slope but then there is a decent amount of variation in the velocity. So i am looking at this right or am I doing something wrong.

Background, I ran the OPEN Cap python example "example_COM_analysis.py" and segmented for a gait cycle.

I wasn't sure if this was an issue for OPEN Sim or OPENcap.

Thanks.

[Krish Narotam]

Also, does anyone know where to find the frame/how they calculated the center of mass. I cannot find that in the documentation for OPENSim.

Thanks.

[Matt Petrucci]

Hi Krish,

Assuming that the participant is moving in a straight line (not on a treadmill), it looks like they reach steady state pretty quickly (which would give you a near constant slope in the position data like you are seeing).

If you want to double check you could differentiate your position data to see if it matches. The sample rate is whatever you set your fps at the start of your data collection.

Hope this helps,