LONDON -- From ice baths to hyperbaric oxygen chambers and cryotherapy rooms, the world's top tennis players have long since learned the importance of recovery to their long-term success.
And with age, it seems they are even more aware of everything they do between matches, to the extent that even a walk with their children or a simple shopping trip may be rejected for fear of losing that extra 1 percent that might win them a match the next day.
"Fifteen years ago, I would go play squash sometimes on my off days," said Roger Federer, who beat Marin Cilic on Thursday to close out pool play unbeaten in the ATP World Tour Finals. Federer already had booked his place in the semifinals of the event for the 14th time in his career.
"Then you're like, 'Hmm, wonder why you're so tired in the semis? How come you have a groin problem all of a sudden? Playing too much soccer, maybe on the grass?'" he continued. "These things don't happen anymore. I'm not skiing anymore like I used to until 2008. So, yes, especially with sports, honestly, I've cut back completely since 2008, since I had the mono."
At 36, Federer continues to defy the passing of time, his Grand Slam victories in Australia and at Wimbledon in 2017 proving that age is malleable.
Federer has been meticulous about his schedule for many years, sometimes at the cost of his bank balance. His decision not to play the Paris Masters earlier this month meant he didn't complete his required quota of Masters 1000s to share in the ATP World Tour Finals bonus pool, which could cost him up to $1.5 million.
Having won more than $110 million in prize money alone in his career, Federer is more concerned with conserving energy than cash. What sometimes stops him from completely resting, though, are his children.
"The kids keep me busy," he said. "I don't have one. I don't have two. I have four. I don't want to be just lying on my couch, as well. But they also have to be a little bit careful that sometimes I don't overdo it. I like my time with my kids, and I can't control myself other than just to play with them, as well, and go outside."
Former women's No. 1 and 2017 International Tennis Hall of Fame inductee Kim Clijsters once said that she was looking forward to retirement so that she no longer had to say no to her daughter when she asked to go for a walk, so concerned was she about how time on her feet would impact her performance. Clijsters chose to miss the opening ceremony of the 2012 Olympics for the same reason.
Former British cyclist Chris Hoy, who won six Olympic gold medals, once said he would not go to the supermarket because it was too many steps and might take away from the power in his legs the following day. Others, such as doubles player Jean-Julien Rojer, are meticulous about their diet, avoiding anything they feel could impede their performance. "I feel like if I have a Coke the night before a match, or a dessert the night before, I feel like I am a step slower," he said. "It probably has nothing to do with it, but it feels like it does. It helps, or at least I think it does, which is important."
Federer is not quite in the same league as Hoy when it comes to the theory of marginal gains -- the principle that if you improve every aspect of your game by 1 percent you would improve by a lot overall. But it was interesting to read the words this week of his fitness trainer, Pierre Paganini, who told The New York Times that the Swiss star has always been disciplined and interested in his longevity.
Compare that to when Federer was starting out, particularly when he was coached by Peter Lundgren and would indulge in the occasional beer close to or even during an event. Now, many years on, he has molded himself into a disciplined athlete, with a beer only passing his lips when the work is done.
In his first four full years on tour, Federer averaged a shade under 25 tournaments per year. When he began to have more success at the Grand Slam level, starting with his first Wimbledon win in 2003, he immediately cut down his commitments. In the 14 years since, only twice, in 2008 and 2010, has Federer exceeded 17 tournaments in a year. After injuries limited him to seven events in 2016, he will end 2017 as the world No. 2, with just 12 tournament appearances. Less really has become more.
"I think I actually have to work less today than I used to," he said in London this week. "When I do, naturally I do it with quality, because I know every practice counts, every fitness counts, every session matters."
Even the younger players on tour, including American ATP Finals competitor Jack Sock, are being careful. "I'm getting older now, got to take care of [the body] more and more now," the 25-year-old said. "Everyone can play tennis at this level. It's just making sure you are feeling good physically, which will help you mentally, as well."
As in so many aspects of his career, Federer seems to be leading the way. "I definitely see things a bit different [now]," he said.