about body weight when using c3d files

Main Forum
1

Hi,

I am using c3d files to determine joint forces for subjects during walking.

In my c3d files, there is body weight information (groups–processing–bodymass).

Can AnyBody use the weight information automatically? Ortherwise I have to change the body weight in TrialSpecificData (GaitLowerExtremity).

In the c3d file in GaitLowerExtremity, there is no information about body weight (GaitNormal0001 - 0003.c3d). So I guess I have to change the body weight information if I want to use this kind of data. Am I right?

Thanks in advance.

Cheers,
Jerry

2

Hi,

Yes, you are right.
AnyBody does not use the body weight information in the C3D files.
So as you know, you have to input the real body weight in the TrialSpecificData file.

Best regards,
Moonki

3

Thanks for your reply.

Although I need to modify the body weight by hand, I think there is no need to change the body length information in GaitLowerExtremity. Because GaitLowerExtremity optimize these information automatically. Am I right?

Besides the body weight, is there any other things I should care in order to run my own c3d files?

Another question:
My c3d files only have one force plate, meaning that the ground reaction force can only be applied to one foot (say the left foot). During swing phase of the same foot (left foot), no ground reaction force is applied to the other foot (right). Does this affect the hip joint force of the left foot? In other words, does the ground reaction force information of one foot affects the hip joint force of the other foot?

Thanks.

Cheers,
Jerry

4

Hey Jerry!

Just a quick comment. In the TrialSpecificData file, it is possible to make a reference to the body mass information in the c3d file so you do not have to copy it manually for every subject. Just write the appropriate reference in the TrialSpecificData file.

You may have to adjust the initial segment lengths for each subject if the optimizer has trouble finding a solution. This is typically necessary if the subject’s segments are much smaller or larger than the ones specified in the TrialSpecificData file.

Best regards
Michael Skipper Andersen
The AnyBody Research Group

5

Thanks for your reply.

I got this problem solved based on your suggestion. It is really convenient for me to write a reference in the TrialSpecificData file.

However, as for whether the ground reaction force on one foot affects the hip joint force of the other foot, can anyone give me some clue?

Thanks

Thanks.

Cheers,
Jerry

6

Hi,

I got this problem solved after adding [0].

But I still do not quit understand whether the ground reaction force on one foot affects the hip joint force of the other foot.

Cheers,
Jerry

7

Hi,

Even if you have only one force plate information, AnyBody can solve the inverse dynamics.

If you are using the ‘GaitLowerExtremity’ model, then you can fine the “JointsAndDriversOptimized.any” file.

And in the file, you can see the following AnyScript code:

  AnyKinEqInterPolDriver JntDriverTrunk = {
    FileErrorContinueOnOff = On;
    Type = Bspline;
    BsplineOrder = 4;
    FileName = Main.ModelSetup.C3DFileData.NameOfFile+"-output-euler-trunk.txt";
    AnyKinMeasureOrg &PelvisPosX = ...HumanModel.Interface.Trunk.PelvisPosX;
    AnyKinMeasureOrg &PelvisPosY = ...HumanModel.Interface.Trunk.PelvisPosY;
    AnyKinMeasureOrg &PelvisPosZ = ...HumanModel.Interface.Trunk.PelvisPosZ;
    AnyKinMeasureOrg &PelvisRotX = ...HumanModel.Interface.Trunk.PelvisRotX;
    AnyKinMeasureOrg &PelvisRotY = ...HumanModel.Interface.Trunk.PelvisRotY;
    AnyKinMeasureOrg &PelvisRotZ = ...HumanModel.Interface.Trunk.PelvisRotZ;
    AnyKinMeasureOrg &PelvisThoraxExtension = ...HumanModel.Interface.Trunk.PelvisThoraxExtension;
    AnyKinMeasureOrg &PelvisThoraxLateralBending = ...HumanModel.Interface.Trunk.PelvisThoraxLateralBending;
    AnyKinMeasureOrg &PelvisThoraxRotation = ...HumanModel.Interface.Trunk.PelvisThoraxRotation;
    Reaction.Type={On,On,On,On,On,On,Off,Off,Off};
  };

We call this forces and moments as ‘pelvis residuals’.
And there is the descriptions about this on wiki:
http://wiki.anyscript.org/index.php/All_about_Kinetics#Why_is_it_ok_to_have_a_reaction_force_between_the_pelvis_and_environment_if_you_have_measured_ground_reaction_forces.3F

And of course it will give you the best result if you have two force plate input data for both feet.

In your model, you may be able to find that the pelvis residuals are higher than normal case because you have no force in the opposite foot.

So if you want to get more accurate result , then I would recommend you to use two force plates.

I hope this may help you.

Best regards,
Moonki

8

Thank you for your reply.

From my understanding, the ‘pelvis residuals’ are caused by the unballanced measured ground reaction force and the body weight (upper body). The ground reaction force transmitted to the plevis cannot offset the upper body weight, causing the residuals. Am I right?

Does these residuals affect the hip joint forces which are my research emphasis? If so, could you explain the reason. Because I really cannot understand how can the ground reaction force on one foot affect the hip joint force of the other foot in inverse dynamics.

And if the hip joint force is not accurate due to the lackage of the other one force plate, is there anything I can do to enhance the accuracy? Now all of my data contain only one force plate. I think it is better for me to just modify the codes in GaitLowerExtremity.

Thanks again.

Cheers,
Jerry

9

Hi,

What I told is that the absence of the force data on a foot may affect the value of pelvis residual force.

To check, the I’d like to suggest you to test on the default GaitFullBody example.

Please try to remove one Force Plate Data applying on a foot.

And try to compare the joint reactions and pelvis residual forces.

Best regards,
Moonki