Scaling Passive Muscle Force Property with Strength

[Margaret Van Horn]

Hi,

I am working on developing a model and found that some of the muscles in my model are weak when I run Static Optimization (high reserves for a given DOF and muscles maxing out at 1 when they activate). Consequently, I scaled up the maximum isometric force property for these muscles which resolved the issue of high reserves and maxed out activations but I am wondering if it physiologically makes sense to also scale the passive force property (FmaxMuscleStrain) proportionally to the amount that Fmo was scaled? I am planning on running CMC eventually and these high passive muscle forces are an issue and lead to very high reserves. I have read about other models scaling up weak muscles but have not seen anything mentioned about this passive force property.

Thanks for the help!

[Emil Walczak]

Hello!
Static Optimization tool does not take into account muscles passive forces, but CMC does.

[Emil Walczak]

Hello again!

I'm having the same problem as you but with CMC, I have calculated the forces produced by residual actuators and compared with the sum of forces produced by muscles and it turned out that there is some kind of unnecessary activation of actuators which provokes maximum activations in the muscles. In the attachments there is a .png file with diagram of those forces, you can observe that shape of the curves are corresponding to each other.

With what model are you working? Are you expecting to obtaind low levels of muscle activation during CMC?

[Margaret Van Horn]

I am expecting low levels of activation in some muscles but also high levels in others. My question really is a physiological one though -- I am wondering if when a muscle gets stronger (i.e. its maximum isometric force property increases) does the passive muscle force property also scale proportionally with it so that the overall muscle stiffness stays the same? To me it seems like it would, but before I incorporate this is my model I wanted to see if anyone had any other opinions on this topic.

Thanks!

[Emil Walczak]

That is a good question. In all muscle models the passive force is in some way related with maximum isometric force.

We can considere that muscles of person who is training are stronger than a normal person, maximum isometric force is related with number of sacromeres that can be activated so when someone with stronger muscles has higher number of sarcomeres in the muscles. Sarcomere are combined into muscle fibres, since passive force of parallel elastic element is a result of conjonctif tissue that combines muscle fibres into the muscle i think that we can consider that if there is more sarcomeres in the muscle -> there is more muscle fibres -> more conjonctif tissu -> passive force is increasing. What do you think about that?