Large and Increasing FY value in RRA

[Julian Atkinson]

I have written a script to run through an OpenSim pipeline for a number of subjects, with two sessions per subjects (8 weeks apart).

I am getting high FY values for RRA, but only in the second session for each subject. It seems really strange! I have compared the force plate forces across sessions, as well as IK and ID, an they seem to be the same across sessions, and the results only seem to differ when it gets to RRA, where suddenly FY is way out. All of the FY RRA values seem to end around 52.

The only thing I can see is that the subjects are the same weight across sessions (8 weeks apart). Can small changes in weight, gain or loss, account for such large RRA values?

Thank you for your help
Kind regards,
Julian

[jimmy d]

Your initial scaling of the model makes a big difference to your RRA values. I would suggest going back to scale and asses your marker placement and scaling.

[Julian Atkinson]

Hi James

Thank you for your response. Just a bit more background. There are 7 trials per session (1 static and 6 dynamic). I scale a model using the static trial per session. The scaling is very similar between session 1 and 2. The scaling errors are low for both sessions. But only session 2 appears to have the problem.

Regards,
Julian

[Thomas Uchida]

The scaling errors are low for both sessions.

Perhaps it is a marker registration issue (which may not be evident from looking at scaling errors alone)? Also note that there's a webinar on the OpenSim YouTube channel that discusses Scaling: https://www.youtube.com/watch?v=ZG7wzvQC6eU.