Millard Equilibruim Muscle Model Strain factor

[Julie Iskander]

In Millard2012EquilibriumMuscle, the FiberForceLengthCurve uses to strain factors to shape the passive force-length curve
According to the documentation
https://simtk.org/api_docs/opensim/api_ ... ml#details

strain = (l-l0)/l0, where l is the current fiber length and l0 is its resting length.

but when plotting the curve, I notice that strain is calculated wrt to optimal fiber length not resting length!!

Do the model treat resting length==optimal length???

Thanks,

[Thomas Uchida]

The default value for the "strainAtZeroForce" parameter is 0, which corresponds to a "resting length" equal to the optimal fiber length. There are some inconsistencies on the documentation page you have cited; I will make sure the page is corrected in the next release. You may also want to consult Millard et al. (2013) "Flexing computational muscle: modeling and simulation of musculotendon dynamics" (http://nmbl.stanford.edu/publications/p ... rd2013.pdf); the passive-force-length curve shown in Fig 3(c) was generated with default parameters.