The secret to Roger Federer's staying power isn't exactly classified information, says Federer's former coach Stefan Edberg.
The Hall of Famer, who coached Federer for two years, says it's clear why the Swiss remains a Top 5 player as he approaches his 39th birthday on August 8th.
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Edberg says Federer is "almost the perfect tennis player" and is fueled by a constant quest to improve.
Speaking to friends and fellow Hall of Famers Mats Wilander and Boris Becker on Eurosport's Tennis Legends podcast, Edberg said Federer's all-court skills separate him from the rest.
"Like I said to Roger, he looks so easy when he plays," Edberg said. "He floats around the court. He's got grace. He's got power. He's got touch. He's got everything you wish for. He's almost the perfect tennis player as I see it—both on and off court. So he's very special like we all know."
Though Federer did not win a Grand Slam championship working with Edberg, the Swiss stylist won 11 tournament titles and contested three major finals.
"You were an invaluable coach for two years and will be my idol for life," Federer said of Edberg after the pair ended their partnership in 2015.
Edberg said the biggest challenge coaching Federer is his knowledge of the court and the sport is so vast, there's a limit to what a coach can bring to his game.
"It was a great two years and obviously it was an honor to be asked by Roger," Edberg said on the Eurosport podcast. "It took me some time to decide. We actually spent a week in Dubai just to get to know each other before going on tour. To summarize the things it was great to be around Roger. He's such an ambassador for tennis.
"Obviously, yes we talked about tennis, about strategy. Obviously, he wanted to change his game and that may be part of the reason why he took me—to get a few ideas. He knows so much about tennis there's only so much you can sort of learn him. Because he knows pretty much everything on the court."
The 20-time Grand Slam king offered insight on Edberg's influence in an interview with Simon Briggs of the Telegraph.
“We took a similar approach in training,” Federer said in 2014. “Stefan reminded me to keep on playing points, whereas before I would only do that when the next tournament was close. I think it actually helped me to remain in a good rhythm. When you take a direction like that, you’ve got to stick with it and see if it works out. For me it did, because I’ve had no recurring issues any more with my back.”
One of only two men in the Open Era to hold the No. 1 ranking in singles and doubles simultaneously, Edberg said Federer's willingness to attack more and switch switch from a 90-square inch Wilson Pro Staff to a more powerful 97-square inch sized version of the frame back in 2014 were game-changers.
Federer, who grew up playing with an 85-square inch Wilson Pro staff, gained easier access to power on his one-handed backhand and serve going to the more modern larger stick.
"Trying to change the game, once you get older you need maybe to change your game," Edberg said. "And that's how we worked on a lot. I think the great thing, looking back, is he changed racquets to more of a modern racquet and that was really a key.
"He changed his game a little bit, his movement. He got a little more aggressive which I think he needed to do. So it worked out very well."