Hello,

I’m interested in the force-length relationship of the 3 elements muscle model in AnyBody system. However, in the tutorials, I did not find any equation related to a few parameters (FcFast, Jt, Jpe, K1, K2 and PEFactor, Epsilonbar,Gammabar ). In the literature, there are equations related to the Hill muscle model, but they don’t use the same nomenclature as you do. For example in OpenSim system are used other parameters, for example:

- ε = 0.6 , passive muscle strain due to maximum isometric force;
- k= 3 an exponential shape factor ;
- 0.033 tendon strain due to maximum isometric force,
- tendon strain above which tendon force is linear with respect to tendon strain
- k= 4 - an exponential shape factor for the passive force-length relation
- γ = 0.5 , a shape factor for the Gaussian active force-length relationship
- 0.3 a shape factor for the force-velocity relationship

I feel confused. Could you explain to me why such parameters are used in AnyBody? And how the muscle force is counted (active, passive) based on them? I will be grateful for the literature. I found some articles, but there is not everything explained there. Do you know if OpenSim and AnyBody use the same Hill muscle model and there are only other nomenclature?

Thank you.