Output files of plug-in-gait_simple model

[Nickel_Lee (Li Hongwei)]

Hello,

When I used my own C3D file to investigate the right knee reaction joint forces, there was 5 output in the

Right/Leg/Jnt/Knee/Constraints/Reaction/Fout
(Mediolateral Force, anteroposterior Force, ProximoDistal Force, Axial Moment and Lateral Moment).

Also, there are other fonder named RefFrameOutput which have 2 part: F and M.

I was wondering what the difference between them.

Any help would be appreciated.
Thank you!

[CDzialo (Christine Dzialo)]

Hello,

Fout gives all the components of the reaction depending on the type of joint. In this case the knee is modeled as a revolute joint, so there are five reactions (for the 3 locked translations and 2 locked rotations) and no reaction for the one free rotation about the medial-lateral axis (flexion-extension moment).

RefFrameOutput.F is the reaction force in the joint, displayed as an array of 3D force vectors in global coordinates associated with the reference frames (in this case the Thigh.KneeJoint and .Shank.KneeJoint reference frames)

RefFrameOutput.M is the reaction moment in the joint, displayed as an array of 3D moment vectors in global coordinates associated with the reference frames (in this case the Thigh.KneeJoint and .Shank.KneeJoint reference frames)

Hope this helps.

Best Regards,
Christine

[Nickel_Lee (Li Hongwei)]

Hello,

Thank you for your response.
So we usually use Fout to investigate the JRF rather than the RefFrameOutput, am I right?
Or could you possibly explain a little bit about the difference between applications of two?

Thank you again!

BW,
Lee

[CDzialo (Christine Dzialo)]

Hello Lee,

It really depends how you want to interpret the joint reaction forces and moments.

To investigate JRF we usually use RefFrameOutput measures (F,M) which correspond to the KneeJointReactionMoments (F and M) found in the BodyModel.*.Leg.MomentMeasure folder (see AMMR\Body\AAUHuman\LegTLEM\LegMoments.any for more info) and then also read up on the AnyForceMomentMeasure function in the reference manual. RefFrameOutput.F and .M measures are arrays depending on how many reference frames are listed. Since there are two (ThighNode and ShankNode) the 1st set refers to the 1st mentioned ref frame, and the second refers to the 2nd mentioned ref frame (measures should be equal but opposite).

SelectedOutput: terminology

Hi Brent, What happens is that the output Reaction.Fout of a the joint gives the reaction forces that the first node applies on the second node of the joint, in the first node coordinate system. And the AnyForceMomentMeasure gives the forces that are applied to the first node, in the first node coordinate system. That is why you found the two are opposite. Best regards, Sylvain.

Hope this clarifies a bit.

Best Regards,
Christine