There's some truth to that for sure. Although Mac was a peculiar case in that he didnt' do much training off court early on. (he did all kinds later) Mac did have the gift (as do most pros) off being naturally fast and quick (and you can't put that in, if you don't have it to begin with) But a lot of that is simple genetics. Nadal, certainly doesn't train harder or more efficently than say...Lendl...or Borg...or Muster...or Courier! The biggest advance though...and it is a big one...is doping. I am NOT pointing fingers at Nadal here....I think it's widespread...and no tennis player is big enough just to tell by looking. I will say that Nadal has to be even more a freak to look like he does, when you consider that nobody in tennis has ever come along and looked naturally like him....he is not huge by any means, but frankly, it's hard NOT to be kind of scrawny, no matter how hard you hit the weights, if you are seriosly running around on court 4+ hours a day. However, it's possible that Nadal is natural and Federer is doping. You can't tell form appearance anymore than you could tell Mcenroe took steroids, or Korda, or Coria...etc.