These results represented, in the minds of some, the start of a career plateau for the then-32-year-old, with back injuries among the factors blunting his dominance.

The whole of 2013 had been a career low for the Swiss champion. Usually No.1 or No.2 in the world, he’d ended the year ranked sixth. A premature exit from Wimbledon, in the second round, had marked the first time in 36 consecutive grand slams that he had not made a quarter-final. He’d lasted until just the fourth round in the US Open, a tournament he’d won five times before.

Federer had broken with a decade of tradition and got himself a new racquet.

A real-life glimpse of Federer was enough to transfix even the most casual tennis fan but, on this occasion, if you were in the know, it was his equipment that would have held your attention as much as the tennis God himself.

His perfect hair held by a perfect headband against a pressed polo shirt, Roger Federer walked on to centre court at the Queensland Tennis Centre for his first tournament of 2014 to an adoring crowd.

How do stars such as Federer, his on-court arch rival Rafael Nadal and Barty and Williams set up their racquets to boost their games? And how have changes in racquets over the years changed the game itself?

More recently, in the lead-up to this year's Australian Open, eagle-eyed fans might have noticed that Serena Williams has stepped out with a new racquet.

For Federer, at that moment in Brisbane, the stakes could not have been higher.

At the elite level, there is nowhere to hide. Just as any adjustment in stroke will be identified and perfected so will every variable gram, inch or centimetre in a racquet be scrutinised. The racquet is the player’s key weapon and one with which he or she has a symbiotic relationship. If a change is to be made to this set-up, it will be for good reason. And even an improvement of 1 per cent is a good reason in international tennis.

For a certain weekend warrior type of tennis player, changing racquets might offer a seductive solution to a subpar game. After all, it’s easier to spend a few hundred dollars on new equipment than it might be to work on a weak backhand or sluggish legs.

He hired a new coach – his childhood hero, six-time grand-slam winner Stefan Edberg. He set about mending his body. And, perhaps less obviously until he appeared on court in Brisbane, he changed his magic wand – the racquet he’d wielded through his rise to tennis legend.

You can tell a lot about a tennis player by how they calibrate their racquet. The tiniest specification will reflect their style in the way reading palms can reveal details about a person’s past, present and future.

A racquet can be a maximum of 29 inches long while the hitting surface (the head) cannot be more than 15.5 inches in length and 11.5 inches wide. Strings must be laid “flat and consist of a pattern of crossed strings, which shall be alternately interlaced or bonded where they cross. The stringing pattern must be generally uniform … not less dense in the centre than in any other area … and strung such that the playing characteristics are identical on both faces.” So no two-sided racquets then. But within these parameters, even the slightest variation makes an enormous difference, as the champions demonstrate.

There are other limits on how much they can soup up their equipment though.

There is nothing in the International Tennis Federation’s rules and regulations restricting what a racquet can be made from, only that it cannot have batteries in it. “No energy source that in any way could change or affect the playing characteristics of a racquet may be built into or attached to a racquet.” In principle, at least, that would seem to leave open the way for all sorts of materials – bamboo? titanium? – and customised touches – diamond-encrusted head? fluffy handle? – that make prevailing racquet technology, and professional players' choices, seem relatively streamlined.

In the heat of contest, Federer did not have to give the change a second thought.

His updated model, the Wilson RF97 Autograph, had a 97-square-inch head, designed to help him hit a heavier shot with more ease. A bigger head means a bigger sweet spot, which helps on defensive shots, for example, when a player is scrambling to get to the ball.

Finally, after some off-season trial and error, he was ready to step out with a new weapon.

Recognising the weakness, Federer tested a new racquet at a German tournament in mid-2013 but reverted to his Pro Staff 90 to end the season, wanting to test more equipment in practice before making a permanent change.

Bigger racquet heads, such as Spaniard Nadal’s 100-square inch frame, packed more punch. Federer’s 90-inch head, combined with back injuries, meant he was starting to be overpowered on court, particularly on his backhand and even more particularly by the monstrous topspin inflicted by Nadal, who had become the world’s No.1 player.

Before his 2014 change, Federer used a Wilson Pro Staff 90, with a smaller head than most modern-day equivalents. It was widely considered to be the closest thing to the classic, smaller-framed racquets of yesteryear. This had been perfect for his controlled and meticulous game. Perfect, in the sense that he had used it to lift 17 grand-slam trophies.

“Rafa is a creature that has been created around his [racquet] frame,” says Australia's Todd Woodbridge, a 22-time grand slam doubles winner.

But what of Nadal, the player who, in part, triggered the change?

Federer made the final in Brisbane that year but lost to Australian Lleyton Hewitt in a shock result. Yet his career did not plateau: he has won three more grand slams and has been a runner-up four times since. In fact, Federer’s racquet change is widely regarded as one of the keys to his post-2014 resurgence.

“I feel like I am not thinking about it [the new racquet] when I am going out there, which is a great thing,” he said after that first competitive match with the RF97 Autograph in Brisbane ended in a straight-sets win over Finland’s Jarkko Nieminen. “I am hitting the ball really well, so I am very pleased with the racquet.”

“If I put Roger's racquet into Rafa's hand, he'd [Nadal] be nowhere near the player that he is. He would still be good but he wouldn't be able to do the things that we see from him – his famous shots, his stock things. That's how much of a difference a piece of equipment can make.”

Nadal’s Babolat AeroPro Drive has a 100-square-inch head, three inches larger than Federer’s.

The world’s best players, including Federer, hit with heavy topspin but Nadal is on another level. He deploys a unique amount of up-and-down “whip” while Federer’s swing is flatter. One reason for Nadal’s big head size is that he needs extra surface area to impart the extreme spin as the ball momentarily slides down his racquet while his arm flings upward.

Another key difference is weight. Nadal’s racquet, made from graphite, as are most modern-day racquets, is 27 grams lighter than Federer’s Wilson. Given Nadal sits a lot further behind the baseline than most players, he has to hit further to land the ball deeper in his opponent's court. The light weight allows him to swing hard with less fatigue to his arm.

Why do some players use gut strings and others polyester?

Federer’s vertical strings are made of natural gut (cow intestine) and his horizontal strings are polyester.

Gut strings are more springy; a ball pinging off gut travels an average of 1km/hr faster than off polyester, according to data from Tennis Lab, a racquet technology company run by Tennis Australia and Victoria University. More springiness also means the gut is softer; less jarring on players’ arms and hands and with a softer “feel” on contact with the ball.

Other gut-string users, unusual on tour, are Novak Djokovic, Serena Williams and Kei Nishikori. All of them mix the gut with polyester. Djokovic plays with an 18x19 string pattern but on a 95-square inch frame. That gives him two more vertical strings than Federer (16x19) even though his head is smaller.

Nadal uses only polyester strings, as do most of his peers. Polyester produces almost 10 per cent more spin, the strings sliding against one another on impact with the ball in a way that causes less friction than grippy gut. Spin is enhanced when strings slide upwards or downwards on each other and “catch” the ball momentarily. As the ball rebounds off them, the strings snap back into place, catapulting the ball further.

Polyester breaks more easily and feels more taxing on the arm – but, for most players, using it has proven worth it.

It will cost an amateur player about $90 to have their racquet restrung with the type of strings Federer uses while going for the polyester-only option, like Nadal, will set you back about $50.

What would happen if Rafa and Roger swapped racquets? Grand slam champion Todd Woodbridge explains:

What difference does the number of strings make?

String customisation doesn’t stop at material. The distance between strings in a racquet head can also impact the behaviour of the ball.

Both Federer and Nadal have 16 strings across their racquet head and 19 from top to bottom but Nadal’s bigger head size means his strings sit further apart. A wider gap between strings holds the ball better before it is launched off the racquet. So Nadal’s prolific spin is supported by his string pattern as well as his string material.

Federer’s string pattern is more closed which, for a player who hits with a flatter swing, means more control. When strings are closer together, the ball rebounds off them at a flatter angle: their trajectory is more direct rather than being flung upwards or downwards by an open pattern.

Control helps Federer when he comes to the net to volley and attack, which Nadal rarely does.

“Control for Federer, with his more closed string pattern, means precision,” says Tennis Lab sports scientist Lyndon Krause. “It’s being able to be precise with where he hits the ball with marginally less spin.”

A brief history of racquets: click right

How big a deal is string tension?

Big. Nadal, famous for his on-court superstitions, never changes his string tension. String tension is measured in pounds: how many pounds of pressure are exerted on the strings when pulled into place in the racquet. No matter the conditions, opponent or surface, Nadal’s tension is always 55 pounds.

Barely more surprising is that Federer, favouring flexibility, carries racquets strung at different tensions, from 57 pounds to 59. His choice might be informed by humidity levels (tennis balls are heavier when it's humid) or just comfort.

The higher your string tension the more of a high-pitched “ping” it will make when you hit the ball. At a lower tension, the ball will thud, or “pock”.

Professional players report their racquets feeling immediately different when the tension is adjusted by even a pound or two – and the effects are real.

A 10-pound drop in tension can increase ball speed by 1 to 3 per cent, a Tennis Lab test of 38 players found, while a 10-pound tension increase can produce up to almost 4 per cent more spin.

“We talk about string tension like a rubber band – the lower the string tension, the more elastic the strings will be, which results in more power. The consequence is more energy is reverted back to the ball,” says Krause.

A lower string tension resulted in balls landing, on average, 54 centimetres deeper in the court than higher-tension racquets, its testing found.

There's an aural dimension to this too. The higher your string tension the more of a high-pitched “ping” it will make when you hit the ball. At a lower tension, the ball will thud, or “pock”. There’s some speculation that players grunt or screech so their opponents can’t hear what tension their racquet is but it’s more likely that they make such sounds as a way to increase the effort and power they hit with or as a result of doing so.

What does stiffness mean?

Another variable is stiffness – the flexibility of the racquet frame.

A stiffer racquet absorbs less energy, so more energy is instead transferred into the ball when hit, thus making it travel further. Federer plays with a slightly stiffer racquet than Nadal. A stiffer racquet amplifies the sweet spot which, for Federer’s smaller frame, is helpful. While Federer gains some “softness” by using gut strings, Nadal may well look for it in a less stiff racquet, which absorbs more energy on impact with a ball and so is gentler on the arm.

String tension, racquet weight, stiffness and pretty much all the variables above can be tinkered with by anyone who has a good enough relationship with their local tennis shop’s staff or stringers.

In September, Serena Williams was using her usual green, grey and black Wilson Blade 104. But in her first tournament since, in Auckland in January, she played with an all-black Wilson that looked a lot like Federer’s. Wilson says Williams is “playtesting” a new racquet but have not released any details. How extensive will Williams' racquet recalibration be?

Certainly, she is as powerful a tennis player as there’s ever been. The head size of her racquet has been 104-square inches, gargantuan even by the standards of the women’s game, where 100 square inches is common as a way to maximise power. Her racquet weight, as with Nadal’s, has been quite light. This helps her swing harder and produce more spin with less effort.

She has played with both a mix of gut and polyester strings and a lower racquet stiffness, which would make the racquet more forgiving on her arm and increase shot power.

An open string pattern, inside her big racquet head, has further enhanced her power and her spin in the same way that it does for Nadal. Her racquet is slightly longer than her male and female peers’ at 27.7 inches (most racquets are 27.0 inches long), giving her more reach.

“There was a period in her career,” says Woodbridge, “In the Australian Open when she went to a thicker frame and she really struggled for a period of time. She started to fly the ball everywhere, couldn't find the accuracy that was needed. So there was too much power for her. So that's a situation of using that right piece of equipment.

“She's one of the greatest servers, male of female, of all time. Put a different racquet in her hand, she would not have the accuracy that she has on serve.”

Ashleigh Barty, who plays with a more conventional, all-round racquet to suit her all-round game, is to Williams what Federer is to Nadal.

As powerful as she is, Barty’s game is more based on craft and guile as she aims to move her opponent around the court and attack the net using her Head Gravity racquet.

Barty’s racquet head is 100 square inches – the same as Nadal's. In women’s tennis, racquet head sizes skew slightly bigger as they look for more power.

Barty is, of course, not as physically imposing as Williams (Barty, for example, is 166 centimetres tall while Williams is 175) so plays with that lighter frame to reduce fatigue and maintain swing speed.

The Queenslander’s racquet is strung with polyester only, reflecting the fact that spin is important in her slice-heavy game.

Barty’s most abnormal racquet variable is her super-soft string tension (40 pounds), which improves power and comfort.

What makes Barty's and Williams' racquets tick? Australian legend Todd Woodbridge explains:

“What I love in Ash Barty's game,” says Woodbridge, “is the slice backhand … She can drop it short, bring her opponent off the baseline but also hit the hard, penetrating ones off the corners. So she's chosen a racquet that a) shecan get a lot of spin on her forehand – that shot allows her to do well at the French [Open] because she can bounce the ball shoulder-height above the women and get shorter replies – and the other one, for her, is a great defensive shot because she needs that because she's only five-foot-five tall. So her particular [racquet] frame, again, is built around her game style.”

Do players follow through when data suggests changing?

“The embrace of technology in tennis, with equipment and analytics, has been slow,” says Tennis Australia’s head of innovation, Machar Reid. He argues that technology should be used to help players choose their equipment better.

A former player and coach and a PhD graduate in biomechanics, Reid runs Tennis Lab, which is part of a broader initiative called the Game Insight Group, made up of data and sports scientists and computer engineers who want to "challenge the status quo" and bring more data and science analysis to tennis.

“If we are to learn from other highly engineered sports like golf and cycling, individual in nature too, and look to what they do really well in terms of customising and fitting equipment better to athletes, what can we do as a sport to catch up?”

Thanasi Kokkinakis, 23, is one of his generation’s brightest tennis talents but injuries have hampered him. He withdrew from a second-round clash with Nadal in the US Open in 2019 due to shoulder problems.

He had used the same Babolat – and the same one Nadal uses – since he was a child. His sponsorship deal with the French company was up late in 2019 so he decided to test other racquets. Could a different brand, an alternative tension, a change in string types or stiffness give him something extra, help him unlock more of his potential? He used Tennis Lab’s Hawk-Eye technology to measure the depth, speed and accuracy of the balls he hit with various racquets.

It [15 grams] doesn’t sound like a lot but when you swing it in your hand over a long period of time with different ball speeds it does help a lot.

“This is the biggest process I have gone through in terms of reaching out to different companies and trying some out,” Kokkinakis says. “I am happy I did it, I had the time, I thought I might as well do it and see what feels comfortable and go from there.”

He didn’t change much, though, despite the data suggesting he was better suited to other racquets.

“I hit with a fair bit of spin and I have learnt to control it because it is a pretty powerful racquet,” he explains. “I don’t want to change the way I play by adapting to other racquets.”

He did go lighter, by 15 grams – the weight of a CD – in the hope that this might improve his injury recovery and fatigue levels. “It [15 grams] doesn’t sound like a lot to the general punter but when you swing it in your hand over a long period of time with different ball speeds it does help a lot,” he says.

Australia’s 2011 US Open winner, Sam Stosur, 35, had a lot of success smashing her opponents off the court in her peak but as she’s gotten older and opponents have become more powerful she has sought to make her game a little more nuanced.

After consulting Tennis Lab, she did change: she played with a racquet that gave her more power and more spin.

Stosur needed to experiment to find a racquet that bridged what the data told her she needed and what she perceived she needed.

However, she found that although she was hitting the ball faster, the significant increase in her spin caused the balls to land shallower in the court, and she was getting hit out of rallies too easily.

Late in 2019, she went back to Tennis Lab and found a racquet that still gave her more power and spin – just, this time, a little less spin. Her balls were now travelling faster and landing deeper in the court so she could control rallies on her terms.

Stosur needed to experiment to find a racquet that bridged what the data told her she needed and what she perceived she needed.

What's in a racquet? Todd Woodbridge recounts his childhood quest to be cool on court:

Can changing a racquet backfire?

Todd Woodbridge knows the risk of changing racquets. Mid-career, he switched to a less stiff racquet to help an ailing elbow.

“I used a really stiff racquet because I could hit the ball flat and hard,” Woodbridge says.

I went back to the equipment I felt like I could play my stock game with.

But a softer racquet meant his “bread-and-butter shot”, the slice backhand, suffered even if his elbow didn’t hurt as much. “I really started to struggle with the feel of that shot,” he says.

“Once you start to doubt that, your confidence goes, you start to lose matches and, for me, there came a point where I went back to the equipment I felt like I could play my stock game with.

“Eventually, I had to get my elbow right [independent of changing racquets] and get the stiffer racquet back in my hand.”

Could today's players win with an old-style wooden racquet?

John Newcombe, 75, a seven-time grand slam champion and five-time Davis Cup winner between 1964 and 1975, used a wooden Slazenger racquet as a child and then a senior version once he began climbing the ranks.

“I didn’t know any different [to the small heads]. In the '70s, when Prince came out with the big-headed racquet and a couple of the guys started using it, we’d say to them, ‘Why aren’t you down the beach with that big spade? You’ll never be able to play with that’.

“You needed a longer stroke [with wooden racquets] and with today’s racquets and the strings you see them hit topspin lobs by hardly moving that racquet head in their stroke. If you did that with a wooden racquet the ball would flop to the ground.”

“I do love watching Ash Barty play. She’s very much in the mould of Evonne Goolagong Cawley, the way she moved the ball around the court and was always thinking ahead – you can see Ash doing that.”

Players of yesteryear would struggle to triumph with today’s racquets, unless they significantly adapted their technique. But the game itself has been changed by developments in racquets, Newcombe contends. Too much power is a dangerous thing.

“It’s probably the major thing that’s hurt the net game,” he says, “because the racquets and strings are so powerful that 10-year-old kids can play terrific ground strokes and hit topspin lobs so they don’t come to the net. They don’t learn the art of net play.

“They’ve got to be careful with the power these racquets are producing,” he adds. “It does take a little bit away from the touch game.

“I do love watching Ash Barty play, for example – she’s not just whacking the ball, I find that style boring and a lot of spectators do, I think. I much prefer players with touch as well as power. She’s very much in the mould of Evonne Goolagong Cawley, the way she moved the ball around the court and was always thinking ahead – you can see Ash doing that.”

The Australian Open runs until February 2.

Graphics | Stephen Kiprillis, Matthew Absalom-Wong Video | Yuji Shimada, Cormac Lally, Kelly Bergsma Editor | Felicity Lewis Thanks to | Todd Woodbridge at Nine, Tennis Australia, Lyndon Krause at Tennis Lab, the Rodney Lack racquet collection.