Low Muscle Activity

Main Forum
1

Hello,

We are using the "Leg Press Model" for our thesis.

When we run the model and look at our MaxMuscleActivity, it's way to low. Do you know what this can depend on? We are using our own "AnyMan" model.

Do you want any of our files? Then we can attach it.

Thank you,

Sofia

2

Hi Sofia,

Please describe which modifications you have made in the model?

Best regards
Søren

3

Line 37 is the only line we have made changes to. The file is a copy of "AnyMan".

HumanModel.any (4.5 KB)

4

Hi Soffan,

It is possible that the model is too strong in this configuration.

You can try to switch to the three element muscle model. Secondly you can try to reduce the max stress value in the muscles this is done in the HumanModel.any file in this folder "Main.HumanModel.StrengthParameters"

Best regards
Søren

5

Hello again,

We tried to change the "Main.HumanModel.StrengthParameters" but we had to multiply it with 0.05 for the MaxMuscleActivity to be reasonable... It's that unreasonable?

Sofia

6

Hi Sofia,

In the standard model the load on each foot is around 25 kg. due to the angle of the sled and maximal activation 12 %.

If I modify the model an try to downscale all strengths by 0.05 i can maximal activations significantly above 1.

It can be that the model is a bit too strong but the load applied in the model is not close to a maximum load, it is more equivalent to a load like standing up, not much more.

Best regards
Søren

7

Hello again,

What to you mean by all the strengths? We only adjusted the "leg" parameter. You should we change all of them?

Sofia

8

It should probably be mentioned that we use a slightly back_rest_tilt_angle and different data points for the movement.

Here is the files some small changes has been made in if you want to try them.
Our files.zip (9.2 KB)

9

Hi Soffan

I have looked the code and spotted an error

  AnyKinDriver KneeDriverRight = {
    AnyKinMeasureOrg  &Knee = ...BodyModel.Interface.Right.KneeFlexion;
    AnyParamFun &KneeData = Main.Parameters.TrialSpecificData.KneeAngleFunc;
  };

This driver will also by default add an reaction force … this means that the driver will take all torque in the knee, and the muscles will do nothing to move the knee.

Add this line into the driver

Reactions.Type={Off};

Then you will see much bigger muscle loads i am sure.

Best regards
Søren

10

Hi,

Thank you very much! This solved our problem :slight_smile:

Sofia

11

Hi again!

Can you help us with another problem? We want to analyse the results in abaqus but we notice that there is some extremely high knee reaction forces, especially Antero Posterior it reaches up to -4700 N which seems unreasonably high. This makes the stress really high in the tibia and femur close to the knee. It should be mentioned that our strenghindex is 0.54 and the barbell's weight is 50 kg a piece. Can you help me with this?

Sofia

12

Hi Sofia,

The model in the AMMR has knee forces on the range of 300-1000 N.

If you get 4700 it can be due to several reasons:

  1. Motion depending on the speed of you motion this can add significant dynamics effect to the model, The AMMR model is rather slow, so if you have a much faster motion it will impact results.

  2. The more the knee is flexed the higher moments it will have to hold, this will increase forces.

Best regards
Søren

13

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