Right. If after exercise, your amino acid count is low, the "make muscles" hormone level will actually drop back pretty fast... This is why the fast intake protein shake thing is recommended if you're trying to bulk up muscle. The main point is that building muscle is a fairly low energy process when compared to actually using the muscle. The energy "consumed" to build muscle is a pretty tiny amount, and so it's not relevant compared to looking at whether you've got the building block components floating around or not.