Joint Reaction Forces in AMMR ADL_gait Database

Main Forum
1

Hello I am working in the AMMR Mocap Example for ADL_gait that uses the Journal of Nature data.

I am specificly looking at the joint reaction forces. I have looked at a couple different parameters and seem to be getting some odd results with competing answers.

I pulled the data from the below two outputs and they don't seem to match.

Main.HumanModel.BodyModel.SelectedOutput.Left.Leg.JointReactionForce.Knee_MedioLateralForce

Main.HumanModel.BodyModel.Left.Leg.MomentMeasure.KneeJointReactionMoments.F

I would possibly expect them to be opposite but they are just completely different. Is the latter the residual forces used to calculate the moments?

Additionally looking at the proximal and distal forces I am getting some odd figures as well. I would expect something like a Paul curve but am getting more of a saw tooth wave.

Thank you in advance,

2

Hi Chase,

the Property "Main.HumanModel.BodyModel.Left.Leg.MomentMeasure.KneeJointReactionMoments.F"

is measured like this:

AnyForceMomentMeasure KneeJointReactionMoments = 
{
  AnyForceBase &Force = ..Jnt.Knee.Constraints.Reaction;
  AnyRefFrame &Thighknee = ..Seg.Thigh.KneeJoint;
  AnyVec3 Mlocal = M*Thighknee.Axes;
};

This is a force moment measure and it will report F as force measured in global coordinate system. This is why it is different from the other measure. This particular measure is not being used to report the force, and the transformation to a local frame has not been done for the the force component.

Best regards
Søren

3

Thank you for the response.

This make sense, thank you for the clarification.

Any ideas as to way I am getting some plateaus on SI load?

4

Hi Chase,

I need a little more info, which variable in the model are you looking at exactly?

Please also share the curve.

Best regards
Søren

5

Certainly,

I am looking at Main.HumanModel.BodyModel.SelectedOutput.Left.Leg.JointReactionForce.Knee_ProximoDistalForce;

I am getting what looks like a saw tooth wave with plateaus at the peaks.

Thank you,
Chase

6

Hi Chase,

Please note that the force is reported in the thigh knee frame not the tibial, this makes a difference in the way the forces are looking.

Which subject and trial are you looking at.

Best regards
Søren

7

Hello again Soren,

Is there anyway to get these loads in the tibial reference frame instead or will I need to do the transforms for that?

The one that I am directly looking at is 2014004_C1_04 though this is not by any fore thought I simply pick one at random.

I'll look at a different one and see if there are issues there.

Thank you,
Chase

8

Hi Chase

Here are some code that can be used to calculated in the shank knee node ref frame

    AnyForceMomentMeasure KneeForceInShankSystem = {
      AnyForceBase &force=  Main.HumanModel.BodyModel.Right.Leg.Jnt.Knee.Constraints.Reaction;
      AnyRefNode &ShankNode = Main.HumanModel.BodyModel.Right.Leg.Seg.Shank.KneeJoint;
      AnyVec3  Flocal =F*ShankNode.Axes;
      AnyVec3  Mlocal =M*ShankNode.Axes;
       };

Best regards
Søren

9

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