In September 2005, Robby Ginepri was supposed to be the next great American tennis player. Unseeded, he had just reached the semifinals of the U.S. Open. Ginepri finished the year ranked 15th in the world. The sleeveless shirts and backwards hats dotted with the Under Armour insignia were to become fixtures on the ATP Tour.

Step aside Sampras and Agassi, a new generation had come. Or had it?

Roger Federer has won 14 Grand Slam titles, Rafael Nadal six. But Federer is not necessarily the better player. Take last years’ Wimbledon, where Rafael took down Roger in an epic five-set match. Federer has a lifetime record of 7-13 against Nadal.

Though Regardless of the “who’s better” argument, Federer may be on track to win more Slams. Meanwhile, Nadal may be nearing end of a very successful, but very short career. Although these two players rule the tennis world, it’s the way they play the game that sets them apart.

Nadal is tough. He hits hard, trains hard and, as a result, wins. Like Nadal, Federer also wins, except Federer is rarely injured where as Nadal is often sidelined (he’s not defending his Wimbledon title because of a knee injury). But how does Federer succeed in staying healthy while Nadal fails?