Adding another note here for people reading at home 😃
Often the temptation when faced with muscles that are 'too dynamic' is to simply make the muscle zMaterial more stiff.
If you're building an organic creature, and have your solver scale set correctly, it's pretty rare that the right choice is to make the muscle material more stiff. This will end up making your muscles feel more like blocks of wood, and you'll lose a lot of the nice local deformation from collisions, etc.