Depends on how intensely you train them.
Personally, I only see progress if I train a muscle group or a particular exercise twice a week. If I squat, deadlift, or bench only once a weak, I wont make any progress strength wise. If I give a full six days off to any muscle group, I wont see much development.
I train with moderate intensity, could go a lot harder. I've been told that the volume I do is out of whack though so IDK.
Well, i don't lift any more than i can handle, i don't push myself too hard because i know that would seriously mess my body up. Maybe i should try the twice a week thing and see how that works.