When I hear that people such drastically changes their life style the person only deserve respect to the dedication and strong character. I actually always had a trouble when I was running, having the colic in my side. That is why I never jogged. But I love all other fitness exercises. To tell the truth lately not regular, but I try to take stairs at my work from 0 to 5th floor and in other building from 0 to 12th floor. Like you I noticed the first time it was so exhausting but now it is relatively normal. It is unbelievable how little our body needs to get used to such regular exercises :)