When was the last time we saw Djokovic get tired? He completely outlasted Murray in an extremely physical match at this years Australian Open Final, after Murray had had (in his own words) the most brutal and endurance based winter training camp in his whole career. By the 4th set of that match, Murray was completely cooked while Djokovic looked totally fine.
Nadal HAS to have a significant physical advantage over his opponent, or he has no chance.
Nadal usually plays from a defensive position, yet he almost ALWAYS outlasts his opponent. If you have ever played the game, you know how unusual it is that the defensive player outlasts the attacking player.
Nadal, Ferrer (smoker), Robredo, Ferrero, Brugerra, Costa all play(ed) defensive style tennis with supreme stamina. Definitely Spanish doctors..
Nowadays Novak by a country mile. Nadal is gassed after 2 sets. It's been this way since 2011, I remember in the US Open final Nadal won an epic third set and I wondered if Novak might not be a bit tired after playing a 5 setter in the semis but then Nadal was the one who was completely done physically in the 4th.