Millard2012EquilibriumMuscle Active Force Length Curve

[Jonathan Mortensen]

Can anyone tell me why I am unable to change the minimum value of the active force length curve in the Millard2012EquilibriumMuscle model? It seems set to zero. If I change it in the GUI, the value reverts back when I hit enter. If I change it in the xml, it is still zero when I check it in the GUI. My understanding is a minimum value of zero leads to long simulation times, and I would like to change it to 0.1. Any ideas?

Thanks,
Jon

[jimmy d]

Not sure why exactly, regardless, from the class documentation;

When either of these singularity-free formulations is selected, the minimum active-force-length value and the minimum permissible activation are set to zero. This is done as a convenience for the user, as these changes make the results of the model more realistic yet incur no performance penality. The maximum pennation angle is left as acos(0.1) or 84.3 degrees, as allowing higher pennation angles results in an increasingly stiff fiber velocity state as pennation angle increases.

So you may not need to set this to 0.1 anyway.

[Thomas Uchida]

Matt's paper describes these issues in detail.

Millard, M., Uchida, T., Seth, A., Delp, S.L. Flexing computational muscle: modeling and simulation of musculotendon dynamics. ASME Journal of Biomechanical Engineering 135(2):021005, 2013. http://nmbl.stanford.edu/publications/p ... rd2013.pdf