Model Scaling - non-physiological position of foot

[Claudia Ghidini]

Hello,

I am scaling an opensim model to analyse data for a participant who is a prosthetic user. The participant wore a running blade and their shoes for data collection.

When I scale, the errors etc are reasonable however, the foot position on the prosthetic side is wrong. I have made the ankle a free joint so that it could move in non-physiological ways. However, I keep getting the same results.

Anyone has any suggestions?

Thanks so much!

[Jon Stingel]

Hi Claudia,

Based on the first image, it seems like the right foot is okay, and that the issue is with the left foot?

A couple of thoughts:

• What are your goals for the project, and is there a reason to use the same generic foot in the model rather than something more specific to your participant or study?

• Have you checked to make sure that all of the markers that you want to move, or that you would like to be locked to their respective bodies in the model are designated correctly with the <fixed> flag? This allows you to specify which markers can be freely moved with respect to the frame they are attached to.

• Since editing the ankle joint to be more free, have you ensured that it is able to reach the full range of motion that you might want it to?

• It looks like you have more experimental markers than markers in the model, you could consider testing different combinations of markers that you are using for computing the scale factors in the foot.

Hope this helps!
Jon