I noticed it this summer while helping my father in law move a pile of top soil. Whereas before I would have been reduced to a whimpering and gasping wreck after a few wheelbarrow loads, I was able to move over half the pile and I still felt I had energy left. I even notice that I have more energy while doing mundane things like climbing a couple sets of stairs. Before I'd just plod up the stairs and now I practically run up them. This simplefit stuff is great :)
I think I'm going to wait a little longer before tackling rock climbing. I'm still a little on the heavy side and my grip isn't up to snuff yet.