I spotted a somewhat old post over at Leangains.com and it was very refreshing to see a post ( and link to a clinical study ) showing not only that exercising fasted didnt result in lower anabolic responses, but actually increased anabolic signalling post workout, our old friend P70s6K!
There is a current stigma in thinking that one should not exercise fasted, especially if its high intensity, because your body will catabolise muscle for energy. It was interesting to see Martin at Leangains speculate on the theory of anabolic rebound and this is something I truely believe is real.
Basically, if your body needs to break down extra muscle protein during working out for energy, this breakdown actually creates a cellular "debt". And, that debt is repaid later with interest. Not only does the study that leangains.com links to suggest this, but this actually happens in other circumstances that were already aware of.
What happens in extreme short term fasting? You loose weight, but as soon as you go back to eating, you gain the fat back and more! Your adipocytes saw that weight loss as a short term loan, and they forced you to repay the debt with interest by manipulating the hormones that make you feel hungry and full.
Again, the same cellular behaviour is seen with regards to sleep. If you get little sleep one night, you tend to oversleep the next night.
This is why I firmly believe that muscle cells are also "educated" on the behaviour of cellular debt.