Roger Federer's former fitness trainer explains secret to the Swiss' longevity, says Federer has "always been very happy" on tour

During a recent interview with Sebastian Torok of La Nacional, Roger Federer's former fitness trainer Paul Dorochenko revealed how the Swiss maestro managed to prolong his career in constant defiance of Father Time. Dorochenko also explained the secret to Federer's happiness on the tour.

Dorochenko specializes in osteopathy and was an important figure in the Roger Federer camp in his early years. The physio was previously interviewed by Torok in 2011, when he claimed that Federer might end up playing until he was 40 years old.

The Argentinian spoke to Dorochenko again ahead of Federer's 40th birthday on Sunday, requesting the physio to explain just how the Swiss maestro has managed to compete for so long.

In response, Dorochenko asserted that there were two main aspects behind Federer's longevity - his mindset and physical conditioning.

Dorochenko claimed that many tennis players don't like life on the ATP tour, since playing, training and traveling regularly gives them little time to revel in their success and spend time with their family.

However, Dorochenko asserted that that wasn't the case with Federer, who apparently felt at home on the pro tour right from the beginning of his career. Dorochenko also said that Federer got along with most tennis players in the locker room, which is another reason why he has always liked life on tour.

"Most tennis players don't like traveling from hotel to hotel... But Federer has really always been very happy on the circuit. When he is in the dressing room, he is in his world," Dorochenko said in a video on Torok's Instagram.

"He knows everyone he has seen, everyone he has beaten, basically everyone... and that is why he feels home in this world. And that is why despite all the years that he is traveling on the pro tour with his family, he is very happy there."

"Roger Federer is the perfect athlete; he has the speed, endurance and strength" - Paul Dorochenko

Paul Dorochenko then laid out the second reason behind Federer's longevity -- his incredible physical conditioning. The physio claimed that the 20-time Major winner had great speed, endurance and strength even when he was just 19.

"The other thing is a physical matter. Roger Federer is the perfect athlete for tennis. He has the speed, has endurance, he has strength," Dorochenko said.

"When he was 19 years old he preferred to lift about 105 kg on the bench press, he said that even though he does not have incredible muscle strength he had strong reactivity. Besides that, he also played football."

Roger Federer as a youngster

Dorochenko also admitted that he would like for Federer to go out on a high just like Sampras, who retired after winning the 2002 US Open.

"I would also like him to retire on his own terms as Sampras did," Dorochenko said.