In my limited experience, research, coaching help etc, the body needs down time to build from the workloads you give it. Obviously there are various schools of thought, and people are different. Last year I was training hard 3-4 days a week, and this year Im only doing 2 "hard days" as well as 2-3 moderate days...so far Im feeling better with a little more rest.

But again, its relative. Im much newer at this than many people here, and my weeks are maybe 7 +/- hrs. And its mostly short intense work. Threshold, V02, and AC workouts.