Muscle Overload

Main Forum
1

Hi,
I am trying to run validation with Wilke files. I have a problem with “SpinePresureStandingLiftStretchedArms.any”. As you run inverse dynamic analysis, you face a muscle overload warning. The biceps muscle of right hand overloads and it influences the force exerted on L4/L5 disk.
I’d appreciate anyone who can help me to handle this problem, or tell me if the model is not going in a wrong way.
Best regards,
Mohamad

2

Hi Mohamad,

You are right the arms do get overloaded.

Please try to increase the strength of the arm muscles by a factor of 1.3 to overcome this problem.

This you can do by the line below in the main file

AnyVar SpecificMuscleTensionShoulderArm= 1.3*90;

I have been running the Wilke models again with this change and the results is on pair with what was there before, but not identical.

Note also that the numbers in the chart on the pdf file is actually outdated they have been produced with a previous version, this chart should be updated.

Hope this helps, otherwise please write again.

Best regards
Søren

3

Hi Soren,
Thank for your helpful words.
But I’m wondered if it is a true assumption to change the strength of the shoulder arm muscle. There are some other muscles involved in this task, how their strength changes?
Bests,
Mohamad

4

Hi Mohamad,

Increasing the strength of these muscles will make the arms stronger, the spine and legs will have unchanged strength.

If the strength of spine and legs are similary increased it will lead to sligtly different results i assume, for the models having high loads on the arms. The paper do not contain any strength information on the subjects, but it is ofcourse also an option to increase the strength of all three muscle groups.

Best regards
Søren

5

Hi Soren.
Thank you very much Soren. That was very helpful. It led to good results.

Now I’m wondering about the magnitude of the strength index, 1.3 I meant. I tested that if we decrease this amount, it leads to a larger disk pressure and vice versa. How did you get this index? Is it got from literature?? Or is just a number that leads to no muscle overload.
Bests,
Mohamad

6

Hi Mohamad,

I am glad the results are good, this index number will lead to no muscle overload, in the litterature there is a wide spread on what is the maximal stress in a muscle.

Best regards
Søren

7

Hi again,
I am modeling some tasks that lead to muscle overloads that can not be solved with the index you introduced me (1.3), Mr. Soren. Is it a true assumption that I increase this index until I have no muscle overload??
Best,
Mohamad

8

Dear Mohammed,

the standard strength in the shoulder-arm of our model is based on measurements from an old subject. This person was relatively weak, so if you want to model a healthy, young, active subject, you can increase the strength quite a bit!
If you think a person should be able to perform the task that you model then you should increase the strength to a value that does not produce overloaded muscles.

9

Thank you dear Al-Munajjed
That was exactly the way I was thinking.
Best,
Mohamad