Increasing muscle strengths

[Sangjun Lee]

Hi all,
I have a question about increasing muscle strengths.

In this forum, there are many replies that recommend to increase muscle strengths.
I think that the muscle strength is the max_isometric_force in the muscle editor. Is that right?

Then, how can I know which and how much muscle strengths to be increased?
I think that change in max_isometric_force causes change in optimization results,
so I'm wondering increasing muscle strengths carelessly is OK.

Does anyone have any information about this?

Thanks so much,
Lee, Sang jun

[Edith Arnold]

Hi,
Yes, max_isometric_force is the parameter that people are referring to when they say to change muscle strength. Generally, unless there is reason to believe that the subject you are modeling has an atypical force distribution, I think it is best practice to increase all the muscle forces by the same percentage.
I wrote a longer post about this over at the Musculoskeletal Modeler's Kitchen project forum a while ago:
https://simtk.org/forums/viewtopic.php?f=559&t=2482
I also posted a tool there that you can download to read in a model and scale all the max_isometric_forces by a user-defined multiplier. I haven't updated it yet for the 2.4.0 release, so if you use it and do so, it would be great if you could post the updated version back to the project.
-Edith Arnold

[Sangjun Lee]

Hi, Edith.
Thank you for your great answer. It was really helpful to me.

I have some more questions.
I think the increase of muscle strengths surely causes the decrease of the muscle activation,
so I'm wondering whether absolute values of muscle activation results are reliable.

And, according to your advice, some muscles' activation will reach near 1.0 even during normal gait.
Is this physically meaningful?
In this case, how can I compare muscle activation results and EMG data?

I'm very confusing about this.

Thanks,
Lee, Sang Jun