The secret behind Federer's late surge

Pierre Paganini took part in track and field in his youth, and when he first decided to become a coach he was interested above all in working with soccer stars. But it is in tennis, a sport he has never played regularly, where he has made an indelible mark as the key man in the shadows for Roger Federer and Stan Wawrinka.

If they have continued to win big into their 30s, it has a great deal to do with Paganini, the 60-year-old Swiss fitness coach who takes a cerebral approach to working up a sweat.

"A big part of the reason that I'm here where I am today is definitely because of Pierre," Federer told me in a recent interview. Where Federer finds himself now is back in London at the ATP Finals, the tour championship reserved for the world's top eight players.

Federer, now 36, is the oldest man in the field and won all his round robin group matches against Alexander Zverev, Marin Cilic and Jack Sock. Federer has won the prestigious event a record six times.

Though he skipped the entire clay-court season to preserve his body and his spark, he has swept nearly all else before him, winning seven titles, including the Australian Open and Wimbledon, and losing just four matches all year.

Back to No 2 in the rankings behind Rafael Nadal, Federer's winning percentage of 92 percent is his best since 2006, when he went 92-5, winning 95 percent of his singles matches (a season, it should be noted, in which he  did  play on clay).

Paganini has worked with Federer for 17 years, longer than any other member of Federer's current team. Is even he surprised by his man's 2017? "Yes, totally, completely," Paganini said. "You have to be honest. It's a majestic, fantastic year. It's not possible normally."

Paganini, who does most of his work with Federer off the tour in Switzerland and Dubai, has seen only two of Federer's 19 Grand Slam tournament victories in person. In 2009, he was in Federer's box when he won his first and only French Open. This year, he was at Wimbledon.

Paganini said he was very much in the moment as he watched Federer defeat an emotional Cilic on the grass of the All England Club, but when Paganini caught his flight back to Switzerland, he said images kept surfacing in his brain of all the work Federer had done off camera to get back to this astonishing level.

One of the most powerful images was from February 2016, when Federer was still recovering from surgery to repair a torn meniscus in his left knee, the first surgery of his life.

"Rog worked with his physical therapist for two weeks and when we started the fitness training, at the beginning he had to, for example, jog 5 meters and then walk backwards," Paganini said. "It was like he was learning to walk again. You can be the most positive person in the world and there are still moments where you wonder, is he really going to be able to play high-level tennis again?"

The answer has been a resounding yes, although it required another six-month break from competition at the end of 2016. The question is how long Federer, the oldest men's singles champion at Wimbledon in the Open era, might be able to sustain this if he continues cherry-picking his spots and staying fresh in the head and legs.

Paganini says it is entirely up to Federer.

"I think only Rog will know when it's the moment that he'll want to say perhaps this is enough," Paganini said. "Rog does have the biological age of 36 but for me, he has an athletic age that is younger than that and yet he has the maturity of someone well over 40. So it's quite a balance."

Federer and Paganini met when the former was 14 and a new arrival at the Swiss national training center in Ecublens near Lausanne. Federer, the youngest boarder there, was still working through his talent and his temper. When he eventually put together his own team in 2000, he asked Paganini to join him.

"He's made fitness workouts so enjoyable, if they ever can be," Federer said. "I just follow his beat. Whatever he tells me, I'll do it because I trust him. People ask me, do you still do your physical tests and stuff? I don't have to do any tests because I work with Pierre and he knows and sees if I'm moving well or not; if I'm slow or fast; all these things. He's had a huge part of this success, and I'm happy I called him way back when."

Paganini said his methods of training Federer have changed with the years. They used to play other sports like basketball in Federer's youth to add variety but now focus on activities that directly correspond to tennis. According to Paganini, they emphasise complex drills that mimic the multi-pronged challenges of the sport.

"You have to be strong, fast, coordinated and have endurance in tennis and you have to do drills for that," Paganini said. "But you also should never forget you have to use this on a tennis court; not on the road or in the pool. So you always have to create a link between the speed and the athletic way it's used on the court. Nine times out of 10 on the court, the speed is in the first three steps and then you're playing the tennis ball. So you have to train to be particularly strong in the first three steps."

Paganini said he truly believes Federer has not lost a step while acknowledging that full transparency was not the goal. "If there is anything that has diminished, it's for the opponents to figure out," he said with a chuckle.

"When you judge speed in tennis, you have to judge it differently than you judge a 100-metre runner," Paganini said. "You have to judge a great deal the reaction time and how well the speed is coordinated. It's not only important to move fast. You have to move right, and with the nature of the sport, you have to move fast and right for a long time in a match. Rog has proved like others before him that it's possible to do this past 30. I think what we forget with him is the discipline he has had for many, many years. All his life and his philosophy revolve around tennis."