The Hitch said:
Regarding Federes physicality it should be pointed out that he uses a way heavier racket.
Nadals Aero pro drive is 300g. Federers Wilson K Factor is 350g.
Heavier racket means slower shots. His serve is usually above 210 but with a Nadal racket that would be closer to 230 which is quite fast and he maintains that through 5 set matches easy.
In reality, heavier rackets mean faster shots! That is why Sampras put lead tape on his rackets. In any case, the tension of the strings is probably a much bigger factor. So he expends less energy on serve than most players, and his serving speed is barely in the world's top fifty.
We can't say for definite whether Federer dopes or not. But I've been watching him for 12 years and over that period, there have been no suspicious fluctuations of body shape or stamina. Mentally, he improved in about 2003 and mentally, he began to deteriorate in 2008. In 2004, he had no entourage, coach or indeed, management. While this changed, Federer hasn't. This doesn't PROVE anything, one way or the other, but my feeling is that I've only got a limited amount of time and energy to devote to worrying about dopers in sport, and there are far more deserving cases for my scepticism. Federer has dominated the game because of his hand-eye coordination, not by running opponents into the ground, and his games are over so quickly that he uses very little energy per match. On the other hand, having followed cycling and got to recognise the symptoms, I find it very hard to reconcile the fluctuations in form, body shape and stamina first of Nadal, and more recently Djokovic. They both have mysterious injuries and withdrawals, only to return with renewed vigour.
I don't know about Murray, but at one point he was travelling with a large entourage including a doctor, which sends alarm bells ringing. Although I never liked him, I have no reason to think Sampras was doing anything he shouldn't. And while I loved Agassi, looking back it is inconceivable that he wasn't.