Sports Tech: Tennis gets smart, advantage technology
Top tennis players use smart technology to gain an advantage over their rivals.
Forty years ago, Bjorn Borg beat Jimmy Connors at the Wimbledon men’s singles final using a wooden tennis racket. Swedish star Borg won at Wimbledon five years in a row from 1976 to 1980 and then retired from competitive tennis the following year. When he tried to make a comeback in the early 1990s, tennis racket technology had moved on.
Players were using lighter carbon-fibre rackets to hit the ball harder and with more control. Borg initially stuck to his trusted wooden racket and in his comeback year the once unbeatable Swede didn’t even win a set, let alone a game.
Today, tennis rackets tend to be made of composite materials, fibreglass, titanium alloys and ceramics, as well as carbon fibre and, more recently, graphene. Some of them even have sensors in the frame or the handle.
Back in the 1970s, Bjorn Borg’s coach Lennart Bergelin was mainly concerned with arranging travel plans and helping the youthful Borg overcome his fiery temper. He left Borg to his own devices when it came to technique. Borg had taught himself to play and developed a technique that included elements he’d adapted from his other favourite sports: ice hockey and table tennis.
These days, coaches have to be analysts as well as motivators and personal assistants. To try and gain insights into a player’s performance that will provide them with an edge over their opponents, they make use of sensor technology embedded into rackets, courts and even stuck on to players themselves.
The Babolat Play smart racket has a sensor in the handle and an app that syncs via Bluetooth, to track a player’s movement around the court. Information is then sent to a handheld device, which provides a detailed breakdown of what the player is doing and gives them insight into how they might improve. That could be number of shots played, different shots played – backhand, forehand, top spin, slice. Even calories burnt and time on court.
The stats also show where on the racket a player is hitting the ball and how far away from the sweet spot, so they can adjust their swing and approach play accordingly. Too many hits at the bottom could mean the player is hitting too close to the ball, or hitting it too late. If contact is too near the top, the player could be too far away from the ball when they hit it, or missing a step in their footwork as they approach the ball.
Zepp and Sony also produce tennis sensors. Babolat has put a similar sensor into a wristband, but it’s not just playing equipment that contains analytical technology these days.
Playsight, a company founded by former Israeli military officers Chen Shancar and Evgeni Khazanov, uses 3D video analysis techniques designed for Israeli Air Force fighter pilot training to design smart tennis courts.
Four high-definition cameras set up around the court track the height of the ball over the net, serve speed, form and the depth of balls on the court. Like the Babolat Play racket, the system has a workout function which tracks calories burned and distance covered. Former Wimbledon champions Novak Djokovic and Billie Jean King have invested in the technology.
SAP has a data analytics system for tennis, one that uses the same technology that helped the German football team win the World Cup in 2016. This system, developed for the Women’s Tennis Association (WTA), gathers information from the umpire’s scoring system and ball-tracking data from the Hawkeye cameras positioned around the court to check on line calls. The data is organised on the SAP Hana platform, which sends out information and graphics to a coach’s tablet and other connected devices.
“Coaches can see, say, whether the position from which a player hits the ball usually is working during a particular match, or whether the player might need to make small changes,” says SAP tennis expert Jenni Lewis. “One coach recently told us that the data gave him confidence to speak to his player during a match because he knew his observations were based on fact. He told her to take a few steps back at the baseline, give herself more time.”
SAP Tennis Analytics for Coaches is used in 22 of the 57 WTA tournaments during games, where coaches have a 90-second window to speak to their players, but not in Grand Slams like Wimbledon. A SAP database of information gathered on players from all over the world is available for competitors and coaches to look at during all the other tournaments.
“This includes information gathered from the run up to Wimbledon, when players play warm-up tournaments on grass, start adjusting their game,” Lewis says. “A certain shot that succeeds on clay or hard court might not succeed on grass and vice versa.”
According to Dr Simon Choppin from Sheffield Hallam University’s Centre for Sports Engineering Research, analytical data gathered in this way helps a player make more intelligent decisions. “The player can focus on precise areas and learn more about their own strengths and weaknesses and those of opposition players,” he says.
However, Lewis adds that data needs to be gathered over a long enough period of time, across enough matches, to form a useful pattern of how a player is performing.
During a recent Association of Tennis Professionals (ATP) tournament in California, biometric sensors were attached to the players during matches. Again, the data relating to players’ movements was sent in real-time to a single platform that coaches, analysts and the players themselves could then access.
The idea, according to the ATP, was to better understand how a player’s physiology works during matches and training. The next challenge is to guarantee accurate readings in a tournament, with so much other wireless traffic around used by spectators, media, tournament organisers and venue staff.
Choppin says a combination of these analytical approaches will give players and their coaches the information they need. “Sensors in the racket tell you how you swing the racket and cameras placed around the court tell you what the ball does afterwards,” he says, but is less sure that body-worn sensors will provide such useful information.
Lewis says that coaches have told her the next thing they want from their data is context. “A player might hit 80 per cent of their first serves in a certain direction, but on how many of those serves does the player win the point, and how quickly do they win the point?” she says.
Choppin adds that what is missing from tennis analytics software is a way of generating coaching tips autonomously, based on data gathered, about how a player might improve in different situations.
“Google uses this sort of AI to direct advertising,” he says, but he acknowledges that this sort of application would be more useful for the amateur player who can’t afford to pay for a coach.
Tennis players, of course, have their own unique styles. For any AI instruction to be useful, it would have to consider not just what is best, but what is best for that player on that particular surface against that opponent at that specific point in the game.
When it comes to these types of calculations, the best processor around is still the human mind, albeit a human mind trained in high-performance coaching, with an encyclopaedic knowledge of the game of tennis and backed up by a lot of data about their player, the player’s opponent and the biomechanics of both players’ movements.
Technology in the tennis racket
Tennis racket manufacturers use carbon composites to distribute weight around the racket more precisely, to suit individual playing styles. By managing the relative stiffness at various points on the frame, they can adjust where and how the racket flexes during play.
One manufacturer, Head, has just launched its MxG series of lightweight rackets, which incorporate precision-injected magnesium and graphene. Head says this will give players both enhanced power and control. In the past, the company says designers had to make the head bigger to get more power, or smaller for better control (a bigger racket head deforms more on contact with the ball), so players had to choose between the two qualities.
Head’s solid magnesium bridge is designed to accommodate longer free-moving strings, which provides a greater trampoline effect and gives the racket a larger sweet spot. At the same time, deformation of the hoop is reduced, enabling better control.
Wilson Sporting Goods, another manufacturer, has used Countervail carbon-fibre technology in its latest high-performance racket frames. The company says this directs the ball’s energy into the frame of the racket on contact and reduces the vibration transferred into the player’s arm – by up to 30 per cent according to a study Wilson made with the University of Minnesota’s School of Kinesiology.
Wilson says this technology will lessen fatigue during long matches and also help stop players from developing tennis elbow, sport’s most infamous repetitive strain injury.
The aerospace industry uses the same Countervail system to dissipate vibration in aircraft. Developed by Materials Sciences Corporation, it uses a proprietary pattern of fibre in the preform coupled with standard vibration-damping layers.
For the ordinary tennis player, there’s nothing worse than chasing around the court after the balls.
This particularly irritated Haitham Eletrabi, a tennis-loving civil engineer from Auburn University, Alabama. Yet rather than pay a few local young people to act as ball boys and girls, or bring his pet dog to matches to collect the balls, he instead designed a robot tennis-ball collector.
The robot looks like a dustpan on wheels. It uses cameras, sensors and algorithms to hunt down and pick up the balls. Once it detects a ball, it picks it up and places it in the attached bucket.
It is operated like a remote-controlled car via an app that enables users to send it to the net, the fence, or even into the neighbours’ garden, if the gate is open.