Tennis coach, Doctor of Physical Education and Sports V. Koronas¹
lecturer, Doctor of Physical Education and Sports D.I. Tohănean^2
1Apostolos Pavlos Private College, Thessaloniki, Greece
²Transilvania University of Brasov, Romania

Keywords: evolution, tennis rackets, materials, composite

Сorresponding author: b.koronas@yahoo.gr

Abstract

This paper presents the materials used and the changes that have occurred over time, in terms of making tennis rackets. Scientific advances in the field have also marked the evolution of the game of tennis, the type and characteristics of materials used in this direction, determining adaptations and improvements of the general style of play, specific possibilities for technical sports procedures and last but not least an increase in sports performance. The quality of the composite materials used at the current stage in relation to those used in the past (wood and metal) is highlighted. It also reveals the remarkable progress of the last 40 years of composites. The special properties of these materials have made tennis rackets more and more light, but with a higher impact resistance and a reduction of the vibrations felt by the practitioner. This has led to greater comfort and increased lightness in their use in sports. The current technology involves the use of carbon fiber in combination with various types of resins, the resistance being given by the optimization of the angles at which these fibers are arranged.

Introduction. By way of definition, we can affirm that sports with racket are those sports modalities that need an implement called a racket for their practice. This implement, instrument, or tool according to the sport in question, and may have different characteristics: dimensions, construction material, strung or not, etc. [12].

These implements are characterized by being made up of three clearly differentiated parts: the handle (area through which the practitioner holds the racket), the neck (intermediate area of the racket and which is usually long) and the head (area with that the ball is hit) [5].

Tennis is a sport that belongs to the ball sports family, and although it is modern origins date back to the end of the last century, its antecedents are much older [3, 4]. In tennis, as it happens in most areas of life, as time goes by, certain improvements are introduced, and some things change. Logically, tennis rackets have also evolved through the more than 6 centuries of history that this sport has.

"Tennis is boxing, it is a violent sport, one against the other, it is boxing without contact" [9]. Andre Agassi was right; the blows come and one can feel them. It only takes one arm extension, a live instrument called a racket, to receive and hit, choose the trajectory, power and speed of the ball, the shot. A conceptually simple instrument: there is a loom, to which a plate of crossed strings is attached, and a handle. That is all. However, the racket, in its technological evolution of almost 150 years, has not only been crucial for the performance and psychological component of the tennis player, but has also been able to redefine the style of tennis [1].

Research methods and structure. To elaborate this study, we identified mainly several sources of information that targeted materials from which tennis rackets were and are made. There were accessed bibliographic sources that aimed at the field of plastics, composites, and specific patents in the construction of these sports objects but also studies that refer to interdisciplinary fields, of the latter are of interest those with a predilection focused on performance training in tennis. In this regard, various international databases were accessed (Web of Science, Scopus, Springer Link, DOAJ and Google Scholar). We also watched various documentaries and interviews with several manufacturers, video resources that refer to the technological process of making tennis rackets to complete as much as possible the conceptual area of our study topic.

The purpose of this research is to understand the evolution of the materials used to make tennis racket over time, by referring to their characteristics and to the effects felt in the evolution of this sport.

Results. In the early 20th century, the material used for both the frame and the neck used to be mahogany. Nevertheless, it changes in the mid-twentieth. Materials become more important and manufacturing is separated from parts. Thus, the frame will be made of walnut, ash, holly and oak woods. These lightwoods helped reduce the weight of the racket. For the grip, what was sought to improve the grip, so maple, cedar and birch woods were chosen [1].

In addition to the wood, all the rackets carried a metallic nail transversely, seeking more solidity in the center of the tennis racket [2].

Table 1. The evolution of the materials used in making tennis rackets over time.

Until 1930, only closed-hearted missiles were designed. Then, the Coq Sportif brand launches its legendary open-hearted models with three bars. This design will soon be replaced by the open heart without a center bar. In the 40's and 50's, the transition is made from artisanal to industrial manufacturing, using wood and laminates [6].

In the 1950s, tennis was fully established as a sport. Tournaments and competitions as important as Wimbledon and US OPEN appear. Thus, to the enthusiasm generated around these tournaments and their winners, the new tennis rackets from the big brands are named after the championship winners, illustrative being the cases of Jack Kramer or Pancho González, for rocket models from Wilson and Spalding [15].

Changes in the materials used in rackets did not happen until the 1960s, when technology began to take off. The new materials were used in the construction of rackets and a rapid development of the materials began [1].

From highest to lowest stiffness, the most popular materials are:

Wood: From the beginning of tennis, wood has been the predominant material in the construction of rackets. Many frames were made of wooden sheets, and due to the pores of the wood, it absorbs the shocks and vibrations of the rocket, making it less harmful to the arm. Wood is a natural material and therefore the type of tree and the growing conditions have a lot to do with the structure of the wood. In this way, the sheets used came from: ash, beech, maple, birch, walnut, and mahogany [10].

In 1967, aluminum (bitubular) and steel missiles were introduced. The aluminum frames were stiffer, lighter than the wooden ones, they offered more control. Combining these two materials resulted in rockets of greater durability and strength but lacking the ability to absorb vibrations. Manufacturing cost and weight were low, moderate rigidity and ease of processing. It is more suitable for players who want flexibility in their racket and do not have enough accuracy and power [6].

Ceramic: It is a relatively modern fiber from the ceramic family, very rigid and with excellent properties in reducing vibrations. It has the disadvantage of being too heavy and very expensive to manufacture [12].

Fiberglass: It arises in the early 70s. It is a staple in the industry due to its resistance and low cost. The builders developed a first composition of rackets through the combination of these with aluminum. It is somewhat heavy, but its impact resistance is excellent. It is the ideal complement to graphite. It could never constitute a framework by itself, as it would be too flexible [10].

Graphite: Graphite is used in the frame of rackets since it is the ideal fiber to give rigidity to a frame and is usually combined with other fibers. It is a compound of aligned carbon molecular chains that produce a very stiff and light fiber. Graphite provides rigidity and hardness to the plastic resins with which it is mixed. When a racket is made of resin and graphite only, it is said to be 100% graphite even though 40% is resin. If other materials are added we are talking about compounds [8, 9].

Composites: The base of these materials is generally made of graphite and fiberglass, and sometimes of other materials such as titanium and Kevlar mixed with a plastic resin. The stiffness and cost of composite materials varies depending on the exact mix of materials [9].

Boron: It is produced by depositing boron elements on tungsten filaments in a high temperature environment. The result is a very stiff fiber, but excessively expensive. It is usually used as local reinforcement and in very small quantities [12].

Kevlar: Fiber of moderate rigidity, very light, resistant to impacts and with vibration reduction properties. Therefore, it is used as a reinforcing element at critical points in the frame structure [9].

Titanium: Titanium is a metal used in racquet frames because it offers a good ratio of stiffness to weight, it is a combination of ultra-strong titanium fibers with ultra-light graphite fibers. The hardness depends on the orientation of the fibers. The first thing to know is that it is not titanium that has made these rackets so light and manageable. Graphite is 2.7 times lighter than titanium and 2.8 stiffer [7, 13].

From 1990 to 2010 tennis rackets were made from the combination of 80% graphite and 20% kevlar [14, 15] and in the current stage, studies in the field have focused on reliability, but also lower costs have led to the emergence of tennis rackets containing carbon fibers in combination with different types of resins. This combination of materials offers superior strength to new types of missiles if certain placement angles of the component materials are observed [8].

Type of material and the influence of the teaching method of tennis today

The evolution of racket construction materials has led tennis to a new level of sport. As everyone can see, tennis has become more competitive, with new, stronger, and faster hits. This is because the evolution of racket building materials has allowed coaches to use different types of rackets (in terms of size, material, and weight) in their teaching to make teaching more enjoyable, more specialized, more specific and more efficient. This is even suggested by the International Tennis Federation (ITF) as an ideal teaching method. ITF calls it "Play and Stay" and in addition to the other parameters it proposes, also refers to the use of appropriate tennis rackets depending on the age, body type and skills of the student. The teaching method "Play and stay" is more effective, more enjoyable, and faster than the classical teaching method [11]. This teaching method could not be applied without the development of equipment as it is today.

Therefore, the evolution of the rackets now offers the athlete the possibility to choose an individual racket by reference to his own style below and to the financial possibilities. There are rockets for strong flat blows, for rotary blows, for better ball control, rockets with weight distribution either on the head, handle, or center.

Conclusions. Tennis rackets have evolved in over 6 centuries of history of this sport, this evolution being due to a relevant extent to the materials from which they were made. Starting with those made of wood, then with aluminum and continuing with composite materials of different types, we can say that each material or combination of materials, due to specific characteristics, have influenced the actual tennis game (learning methodology, possibilities of technical procedures, how to approach the competition).

The evolution in the manufacturing mode culminates in the current stage with the existence of the possibility for a tennis racket to be made in accordance with the individual characteristics: age, level of training, purpose (professional or amateur), etc.

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