yeah, but you don't have to run when you're playing doubles. i bet the number of players who smoke at least doubles (if not triples) if you compare singles players and pure doubles players.
and mentioning rafa and federer in a sentence with petzschner? i don't know, pretty insulting to the two. petzschner is what, the 500, 600 in the world?
He plays tennis for a living, just like Federer does. So he's a pro. You know exactly that his bad ranking is caused by long injury breaks again and again, currently a torn ligament. I have newspaper articles reporting that Petzschner defeated Al Ghareeb last year in 3 sets because of his superior fitness.