Constraint violations of calculating moment arms

Hi, I'm Dwan Lee.

I currently do modeling for the shoulder model.

And I'm interested in calculating moment arms, however, my model got some errors about kinematically over-constrained.

Here I attached some pictures about the errors when I run the step of "RGHAbductionRight" in "EvaluateMomentArms".


My question is,

Do I need to change the DOF of the glenohumeral joint?

or other else?

Thank you,

Best regards.

Dwan Lee

09/21/2020

This problem has occurred when i set "shoulder rhythm" ON.

Hi Dwan,

The problem is indeed the shoulder rhythm, the moment arm study is by itself kinematically determined, it has all divers it needs, so adding the shoulder rhythm makes it overdetermined.

We now plan to add a warning on this and a mech object exclude to remove any rhythm from the momentarm study.

Having the rhythm on in the moment arm study is not so meaningful since it will make several DOF move simultaneously. The moment arm study works by moving one DOF at the time. You can change the other DOF to have a different constant value but it needs to be constant.

Best regards
Søren

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Hi, Søren.

I really appreciate your answers, and I hope the rhythm problem can be fixed in the future.

I have another question that parameter identification step doesn't affect to evaluate moment arms?

I compared the results of moment arms between adding parameter identification and non-adding parameter identification step during the calculation.

But, the results show no difference between them.

Thank you,

Best regards.

Dwan Lee

Hi Dwan Lee,

If the parameters in the model was found in a previous run the model will start loading these this could possibly explain it?

Try deleting the .anyset file for the trial and try again, also please try to figure out how much the model parameters changed, is it all moment arms?

Best regards
Søren

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Hi, Søren.

I tried to make an upper-extremity model excluding the left arm. Therefore, the parameters were changed related to them (ex. upper arm length, fore arm length..).

By the way, I deleted the previous .anyset file then made a new file. For that reason, the results were changed what I expected.

Currently, I've studied "evaluating moment arms" in AnyBody. And I'm wondering why the angular velocity of joints has to be set 1?

Furthermore, why LmtDot can display as the moment arm in AnyBody? Is LmtDot the current length between a joint center and muscle?

Thank you,

Best regards.

Dwan Lee

Hi @DWAN

It sounds good that you are making progress!
Regarding your questions, I am a little unsure of what you mean about:

"...the angular velocity of joints has to be set 1?"

As to your question about the LmtDot of the muscles, it is the rate of length change of the total muscle-tendon unit (i.e. the velocity).

Here is a link to find valuable information regarding all the Muscle Output parameters.

The LmtDotIt is not displayed as the moment arm in AMS but it is part of calculating it.
You can find the calculation in the EvaluateMomentArmsStudy.any file located in your AMMR under \Body\AAUHuman\Arm\EvaluateMomentArmsStudy.any

Best Regards,
Bjørn
AnyBody Technology

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Hi, Bjørn.

Thank you for your quick response.

"When the velocity of the joint is set to 1 the muscle velocity LmtDot displays the moment arm." - AnyScript Reference

By the way, I already checked the calculation (=LmtDot/Angular velocity of joint).

From the reference, angular velocity always sets 1 for calculating moment arms.

I guess the reason why setting 1 is related to the tendon excursion method.

Best regards,
Dwan Lee

Hi Dwan,

Yes exactly, when setting velocity to 1 LmtDot displays moment arm.
Note that it is important for biarticular muscles that the other joint has a fixed position.

Best regards
Søren

1 Like