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In most countries, football is traditionally played on natural grass. However, for climatic and economic reasons, artificial turf has become a popular alternative playing surface-for example, in Scandinavia. 1- 3 Many pitches are being built, although the risk of injury on artificial turfs is poorly documented. Concerns have been raised that playing on different surfaces and switching between turfs may lead to an increased risk of injury in elite as well as in amateur football. 4- 6 The stiffness of the field surface, its quality and the friction between the surface and shoe are key factors involved in surface-related injuries. 2, 7 Field stiffness affects impact forces and can result in overload of tissues such as bone, cartilage, muscle, tendon and ligament. Friction is necessary for rapid starting, stopping, cutting and pivoting in football, 7, 8 but injuries can result if friction is too high. 9
The first generation of synthetic turfs appeared in the mid 1970s. 10 They had short, thin fibres and were characterised by high stiffness and friction, leading to considerable differences in ball behaviour compared with natural grass. Since then, turfs have been developed with a sand filling, leading to reduced friction and lower ball bounce. In the late 1980s, the second generation of artificial turfs was introduced with longer, thicker fibres, better quality sand fillings and a rubber base under the turf itself to reduce stiffness. 11 These were the first turfs designed specifically for football, however, their characteristics still differed appreciably from that of natural grass. The risk of injury was higher on these turfs. 4, 12 The third generation of synthetic turfs was introduced in Norway in 2000, consisting of even longer fibres (50-60 mm) and filled with siliceous sand and rubber granules to mimic more closely the playing characteristics of natural grass pitches. 11
Some studies on American and Canadian football suggest that the incidence of major injuries and ligament sprains is lower when playing on natural grass than on later generation artificial turfs, 13, 14 whereas others have shown conflicting findings. 15 However, American and Canadian football codes differ considerably from European football in their playing characteristics and injury mechanisms so it is not known whether these results can be extrapolated to European football. A...