@Alex
in short few months 2010/2011 Djokovic improved from player with average physical fitness to superior one to all on ATP
im sure that he was clean in 2010 (win over Federer on UO was just amazing triumph of true champion in every way)
if you ask me for solid proof i do not have any and i offer my apologies if i`m wrong with my speculations
but question about his physical fitness remains
btw
i hope this AO will win Anyone except Fed & Djoko