IndianFootball.Com guest columns: L. SANTOSH SINGH

Need for the Biomechanics of football surfaces

Sports biomechanics is concerned not only with the mechanical functioning of the human body in sport but also with the football surfaces used. The ground on which the game is played also affects the nature of the game. Surfaces for football, particularly football, have evolved in response to both performance and economic requirements. The controversy aroused by the introduction of the synthetic surfaces for football has led to biomechanical investigation into the performance and protection characteristics of all types of surfaces.

There has been much controversy in Britain concerning the use of artificial turf for playing football. It has been more readily accepted in North America, Scandinavia and the Middle East where there have not been the same longstanding traditions associated with the game, or where environmental considerations are important. In other parts of Europe particularly, there is little contemplation of anything other than a natural turf surface. Artificial turf is an issue in football not least because of the economic benefits that may accrue from its use, but also the pressure for its use in many parts of the world.

There is much conjecture concerning the merits of artificial surfaces, but only a little scientific evidence. Much of this was collected in England by a commission headed by Winterbottom and supported by the Football Association and the Sports Council. The first artificial pitch was installed in the UK in 1971 and the first Football League artificial pitch was installed at Queen Park Rangers in 1980. The opinions of players, managers and club chairmen were that football could be played to a high standard on artificial pitches but necessitated a modification to the playing of the game, which often did not suit the British game. Therefore a three-year moratorium was placed on the installation of artificial pitches for League football until Winterbottom's report had been fully considered. The report attempted to obtain scientific data on the comparative performance of both natural and artificial pitches. The author took several example of each class of pitch from various levels of play and conducted a series of tests of performance characteristics. The tests were concerned with aspects of ball surface interaction, player movement and player surface interaction.

Two tests were used to establish the interaction between ball and surface. These were rebound resilience and rolling resistance. The former test established how a ball reacts after hitting the surface and relates to ball bounce, while the later test established how quickly a ball slows down when rolling over the surface. Rebound resilience was found to be 3-6% higher on artificial rather than real turf surfaces, although variation bin ball type at was between 3 and 7%. Variation in rebound resilience due to variations in ball pressure accounted for 4-7%. Other factors, which affected the results, were the spatial location on the pitch where there was less variation for artificial surfaces, and wetness, which tended to reduce the rebound resilience. Various non-systematic effects were produced from the grass species used and the type of material used in the construction of artificial. In addition, as turf surface became older they became more compact and harder, thereby increasing the rebound resilience. The test for rolling resistance showed that this was about 20% less for artificial surfaces. This was reduced when the surface was wet. On turf surfaces spatial location could affect the results. Where the turf was lusher the rolling resistance was greater and where worn it was lower. In both of these tests there would appear to be little difference between the two types of surface under optimum conditions. The turf surface would appear to be the more variable.

The tests used for assessing player movement were tests for torsional traction and sliding resistance between the boot and surface. The torsional traction was measured using a studded plate, which was loaded on to the surface and rotated, stimulating a player pressing the boot down on to the ground and twisting. The torque produced when slipping occurred was recorded. A torsional traction coefficient was calculated, and it was found that there was great variation in this for all types of surface. It ranged from 1.1 to 2.2 for turf surface, and 1.0 to 2.8 for artificial surfaces. It tended to be lower for sand filled artificial surfaces compared to open weave surfaces. A major factor affecting these results was the type of stud and stud pattern, and the results presented on this topic are some of the few in any research which has considered the effect of there variables. There was found to be no difference between surface type, and factors such as surface pile, moisture, and stud pattern and whether the front or rear of the shoe was used are all of some importance. Therefore other factors are more important with regard to sliding friction than the surfaces themselves.

The general conclusion of Winterbottom's committee was that in many respects there was little difference between the two types of surface, but in some importance respects there were. In these respects, artificial surfaces could be designed to make their performance characteristics similar to those acceptable for natural surfaces, and the performance of pitches already laid could be controlled by the use of water to deaden a lively pitch and to provide a better energy-absorbing surface. Although artificial surfaces could be tailored to suit playing requirements, one feature of their performance does not readily match that of real turf, and that is its variability. Generally a natural surface is mire varied both between surfaces and within an area of a pitch, and this is thought top be a crucial element in the game of football. In 1989 the Football league published its final report after the period of moratorium and concluded that artificial surfaces were not suitable for the playing of the game at the highest level in the English League. They were deemed suitable for lower level play where economic advantages of the artificial surface were also of importance. This finding has been endorsed by the international authorities of the game (FIFA), and all competitive international matches are played on real turf. It should be noted that the conclusion reached by the Football League regarding the suitability of artificial surfaces was as much to do with subjective judgments of how the game should be played as with their performance, economic or injury characteristics.

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