Muscle maximum force setting

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1

Hi,

I have a question about the force generated by the muscles. I would like to reduce the force exerted by some spine muscles in the repository human model during the motion, in order to represent muscle weakness or damage. I was thinking of decreasing the maximum force of the muscles, but if during the motion the activity is only about 10%, reducing the max force would only result in a larger activity but with the same output force?
If instead reducing the max force would result in some differences in the forces outputs, could you suggest the easiest way to do it?

In the file MuscleParametersSpineSimpleRight.any, for example, I see that each muscle is defined through the PCSA and the scaling:

AnyMuscleModel MFdL1L3Par = {
      AnyVar PCSA = 0.38; //Physiological Cross Sectional Area in cm2
      F0 = ..StrengthScaleSpine*PCSA *...StrengthRef.SpecificMuscleTensionSpine; //Maximum force output at optimum fiber length
    };

If I wanted to reduce the maximum force that the muscle is capable of producing, would I have to modify each PCSA or shall I change the “StrengthRef.SpecificMuscleTensionSpine” parameter?

Many thanks,

Michele

2

Dear Michele,

  1. If you reduce the maximum force of a muscle, then if may change the muscle coordination so that you may also see a different muscle force as well as different muscle activations.
    As you pointed out, if muscle force is still as same as before even if you reduced the strength then you will only see the different muscle activation. But you should try because the muscle coordinataion will be different based on the relationship of different muscle strengths.

  2. If you want to modify the strength of MFdL1L3Par, then I would only modify the PCSA value. Because every muscle has its own PCAS so that it may make sense to change that value whereas StrengthRef.SpecificMuscleTensionSpine will be shared with other many muscles.

I hope this this can be useful to you.

Regards,
Moon