The problem of simulating a model whose muscles are disabled

[Fateme shahmari]

Hello. Good time.
I want to do a simulation on model (FBLSmodel), but the number of muscles in this model is large, so I kept only a few muscles active. But when I try to simulate, the model falls apart and sinks into the screen.
Please guide me how I can have a flawless model after disabling some muscles of a model.
thank you.