Thorax Ref Frame

Hi,
I am analysing a few models and having a few problems when looking at the hip moment. I think it is something to do with the upper body, and wondered if it was possible to rotate the segment axes for the thorax so that when the mannequin is stood in the upright position, the sagittal rotation is measured at 20 degrees (rather than zero). I have tried to alter the SegmentsLumbar.any file to rotate the axes but this comes up with a warning about a non-orthogonal plane and automatically switches the axis back. Is this the best way to try and achieve this?
Thanks

Hello,

if you make changes there it will affect evrything in the study your complete model might be wrong.
However, you can easily change the coordinate system your reaction forces are displayed/recorded in. When you have a look in the Wiki:

http://wiki.anyscript.org/index.php/Tips_and_tricks#Measure_the_reaction_force_in_a_joint_in_a_certain_coordinate_system

at:

Measure the reaction force in a joint in a certain coordinate system!

So you can get your hip reaction forces in a self defined coordinate system. I hope that is what you want.

Hi,
Thanks for the reply. As changing the ref frame is perhaps not the best idea, is it possible to impose a permanent pelvic throax extension? I some motion capture of the lower extremity which has quite a large degree of sagittal pelvic rotation, but I want the upper body to remain vertically upwards (pretty much parallel to the horizontal plane). I have applied 20degree pelvic throax extension in the mannequin file, which initial rotates the upper body relative to the pelvis. However, during the optimization it reverts back to the 0degree position. Is there a method for the optimization to work with the extension always at the define value.

Many Thanks
Pete

Hi Pete,

In the repository, there is an example called GaitUniMiami. In this example, the c3d file only has markers for the lower extremity and the upper body is fixed at a certain position (I think it is fixed in respect to the pelvis). And therefore the upper body is not used for the motion optimization. This could also help you.

If you take out the upper body markers and fix the upper Body with you 20degree angle.

I hope that works for You!


Hi,
Thanks for the reply. I have tried with the GaitMaimiModel and the same thing happens. Sorry I forgot to mention before that the LowerExtremityModel I am using at the moment has no upper body markers. Therefore I don’t understand why the motion optimisation always returns a kinematical solution with the pelvic-throax extension at 0°, even though this is set to 20° in the mannequin file. Is there a way to permanently impose a pelvis-thorax extension or is it always preset to be 0° when the upper body is driven by drivers rather than markers.
Thanks
Pete

Hi Pete,

the value in the Manequin file is used for the initial position, but not necessarily for the kinematics. Check at the driver and have a look, if it refers there to the Manequin file, or if it uses a different value.

The UniMiami model had something special in it, the Upper Body was driven to have the Centre of Mass above the pelvis, this will then not work in your case.

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