Inverse Dynamics: Plots are upside down?

[Jas K]

Hello,
I have captured some gait data for a healthy control using a motion capture system called motion analysis corporation which involves 2 force plates(Kistler). I digitized the data in Cortex and processed the data in Visual3D.
I exported data from Visual 3D to openSim by following the process outlined in the document available on the Visual 3D wiki documentation. Here is the link- http://c-motion.com/v3dwiki/index.php?title=OpenSim

On plotting the hip flexion, knee and ankle moments against time after performing inverse dynamics; the curves for hip and ankle moments are upside down whereas the curve for the knee is correct. Could this be due the fact that both the Cortex and Visual3D have a different global coordinate system set up as compared to OpenSim?

Thanks
Jas

[Erik Dijkstra]

Hi Jas,

I think the different joint sign conventions in the model are the reason for the curves to be "upside down" for you. We have seen similar things when directly comparing Vicon results with results from OpenSim plots.

You can easily check this by looking at the kinematics.

Hope this helps,
Erik