Everything seems to take different muscles. I'm in really good shape (for my age). I was in France with my sister and niece for a week. We walked a bunch--no problem because I walk, cycle, aerobics--all that stuff. Then one day we climbed to the top of the Arch of Triumph and also up Notre Dame de Paris. The next day I could barely move my legs! And I have stairs in my house--but they don't go up that high! We all gotta cross train!