The start of the Australian Open, the first tennis grand slam of the year, signals detailed discussions of metrics such as points won, serve speeds and shot placement. While many of these performance metrics can, of course, be attributed to the player, we should also consider the important role played by the racket.
Tennis is an old sport with a rich history of technological development in equipment. Wimbledon, the oldest tennis tournament, was founded in 1877, and the first Australian Open was held in 1905. Through the application of advanced engineering, the tennis racket has changed considerably since these early competitions, as detailed in a recent research article and summarised in the video below.
Early tennis rackets borrowed their design from the older sport of real tennis, an early racket sport dating back to around the 16th century and played by the rich and elite. They were made of wood, with long handles and small lopsided heads, which made it easier for the player to bring the hitting surface close to the ground to hit the typically low bouncing balls of real tennis. These soon disappeared as tennis developed as a sport in its own right. Symmetrical racket frames were becoming commonplace by the time of the first Australian Open.
Most manufacturers continued to make their rackets from wood until the 1960s, with few other design developments seen. Some early tennis racket manufacturers did produce metal frames to try and overcome the issue of wood warping due to humidity, but these were unsuccessful.
Not only does metal offer less damping than wood, meaning the player feels harsher vibrations if they mishit the ball, but the metal frame often damaged the natural gut strings at the point of contact. The Dayton Steel Racket Corporation attempted the use of more durable metal strings, but these affected the felt cover on the ball and were prone to rusting.
A technology boom
The start of the open era in 1968, when professionals and amateurs began competing together for cash prizes, was probably a key driver behind the rapid development of tennis rackets seen around this period. During the 1960s wooden rackets were still the most common, but fibre-reinforced composite materials such as fibreglass started to appear as a reinforcement on wooden frames, like the Challenge Power by Slazenger and the Kramer Cup by Wilson.
By the 1970s, racket engineers were experimenting with a range of materials, such as wood, fibre-reinforced composites, aluminium and steel. A key racket from this period was the Classic by Prince, based on a 1976 patent from Howard Head. The Classic was made of aluminium, which allowed for a much larger head than its wooden predecessors and made it easier to hit the ball. Plastic grommets were used to overcome the issue of string (now synthetic) damage experienced with earlier metal rackets.
The Classic set the foundations for the modern tennis racket, with most of its successors featuring large heads. Indeed, the International Tennis Federation began limiting racket size in 1981, so technological developments would not change the nature of the game.
Since the 1980s, high-end tennis rackets have been made from fibre-reinforced composite materials, such as fibreglass, carbon fibre and aramid (strong synthetic fibres). The advantage of these composite materials over wood and metal is their high stiffness and low density, combined with manufacturing versatility. Composites provide the racket engineer with more freedom over parameters such as the shape, mass distribution and stiffness of the racket, as they can control the placement of different materials around the frame.
While wooden rackets had small, solid cross sections, composite rackets have large, hollow cross sections to give high stiffness and low mass. The increased design freedom offered by composites was demonstrated with the introduction of "widebody" rackets, such as the Profile by Wilson, in the late 1980s. Widebody rackets have larger cross sections around the centre of the frame than the handle and tip, to give higher stiffness in the region of maximum bending.
The higher stiffness of composite rackets means that they lose less energy to vibrations upon impact, so the player can hit the ball faster. However, there may be an increased risk of overuse injury to the arm when using a high stiffness racket with a large head. A lightweight modern racket with a lower swingweight (moment of inertia about the handle) is also easier for the player to wield, and they tend to swing them faster during strokes.
Despite the higher swing speed achieved with a lighter racket, ball speeds tend to remain similar as the increased racket speed is counteracted by the reduction in striking mass. There is most likely an optimum racket for each player, rather than a one-size-fits-all solution, and player preference is an important consideration. Customisation techniques and player monitoring using sensor and camera systems are likely to play an important role in the future of tennis racket design.
Modern composite tennis rackets are made using labour intensive processes that are not very environmentally friendly. We may see racket manufacturers exploring more sustainable materials, such as recycled and natural fibre composites, and more automated manufacturing techniques like additive manufacturing. We might monitor how a player swings a racket using a sensor, and then manufacture them a customised racket optimised to their playing style.
The development of the tennis on display at the Australian Open has been bound to the evolving design of the racket. Researchers have calculated that a player could serve the ball around 17.5% faster using a modern racket than with those used by the first players in the 1870s. No doubt we will see further advances in racket design shape the sport into the future.
Author: Thomas Allen - Senior Lecturer, Department of Engineering, Manchester Metropolitan University