It's estimated Nadal ran between 9 an 10 miles in that 2 1/2 hour three set match this morning, if it went five sets, he would have run about 19 miles I'm told.
Then you have to factor in the hand/eye coordination, striking the ball in the process of running thosse 10 miles, carrying that 10 oz racquet, not to mention doing all those gymnastic type splits and what not returning the ball.
Take a look at Nadal, he's 6'1" 185 lbs, ripped, with about 8 percent body fat.
Guy has my vote as the best athlete in any sport alive right now.