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1 This article was downloaded by: [Hughes, Michael] On: 23 September 2010 Access details: Access Details: [subscription number ] Publisher Routledge Informa Ltd Registered in England and Wales Registered Number: Registered office: Mortimer House, Mortimer Street, London W1T 3JH, UK Sports Technology Publication details, including instructions for authors and subscription information: Football-specific evaluation of player-surface interaction on different football turf systems Wolfgang Potthast a ; Rudy Verhelst b ; Michael Hughes c ; Keeron Stone c ; Dirk De Clercq d a Institute of Biomechanics and Orthopaedics, German Sport University Cologne, Cologne, Germany b Department of Materials Science & Engineering, University of Ghent, Ghent, Belgium c Cardiff School of Sport, University of Wales Institute, Cardiff, UK d Department of Movement and Sport Sciences, University of Ghent, Ghent, Belgium Online publication date: 21 September 2010 To cite this Article Potthast, Wolfgang, Verhelst, Rudy, Hughes, Michael, Stone, Keeron and De Clercq, Dirk(2010) 'Football-specific evaluation of player-surface interaction on different football turf systems', Sports Technology, 3: 1, 5 12 To link to this Article: DOI: / URL: PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.

2 Sports Technology, February 2010; 3(1): 5 12 REVIEW Football-specific evaluation of player surface interaction on different football turf systems WOLFGANG POTTHAST 1, RUDY VERHELST 2, MICHAEL HUGHES 3, KEERON STONE 3, & DIRK DE CLERCQ 4 1 Institute of Biomechanics and Orthopaedics, German Sport University Cologne, Cologne, Germany, 2 Department of Materials Science & Engineering, University of Ghent, Ghent, Belgium, 3 Cardiff School of Sport, University of Wales Institute, Cardiff, UK and 4 Department of Movement and Sport Sciences, University of Ghent, Ghent, Belgium (Received 27 February 2010; accepted 25 March 2010) Abstract In order to accommodate the increasing relevance of artificial football turf systems, both producers as well as governing bodies make substantial efforts to bring the game on artificial turf as close as possible to the game played on natural grass. In this context, the certifications for acceptance of certain artificial turf systems are based on pure mechanical tests. Developers modify mainly fibres, infill and elastic layer in order to optimize the mechanical properties of the turf system. Some recent research shows that pure mechanical tests of artificial turf systems do not reflect the interaction between the player and the surface. In complex football-specific movements such as goal kicks or cuttings the players perception, movement and sports performance can change remarkably due to changes in the turf. Those changes are not necessarily reflected in mechanical tests. By basically changing one component (infill), the differences between artificial turfs can become greater than those between natural grass and an artificial system. It is likely that physiological processes are also influenced. Subject tests are recommended to improve the current certification procedures and to provide information to the producers in order to optimize existing systems. More research is required in order to produce baseline data for soccer-specific movements on natural grass. Keywords: Artificial turf, football specific, biomechanical and physiological testing Introduction So-called third generation (3G) artificial turf systems for soccer were introduced about a decade ago. A typical third-generation turf system consists of an elastic layer, the artificial grass carpet and an infill material filling the space between the grass fibres. The systems are usually installed on a more or less rigid substrate (e.g. compacted gravel or concrete). A deformable elastic layer of about 1 3 cm thickness covers the substrate. Various synthetic materials, e.g. recycled styrene-butadiene rubber (SBR), polyurethane (PU), or polymeres are used as infill materials, normally in combination with sand. The infill usually leads to a typical pile height of the fibres of about 3 4 cm. The fibres are usually crimped or straight extruded polyethylene monofilaments. Figure 1 shows the principal construction of an artificial turf system with rubber and sand composition infill. The increasing number of 3G artificial soccer turf fields and the fact that important international games (Champions League, Europa League, qualifying games for the 2010 World Cup) are played on such surface systems shows the significance of 3G artificial soccer systems. Taking the importance of artificial soccer turf into account, governing bodies have developed certification systems for artificial soccer turf (FIFA, 2010). The certifications aim to bring the game on artificial turf as close as possible to the game on natural turf, in order to not increase the risk of injuries and to not disturb the character of the game Correspondence: W. Potthast, Institute of Biomechanics and Orthopaedics, German Sport University Cologne, Am Sportpark Müngersdorf 6, Cologne, Germany. potthast@dshs-koeln.de ISSN print/issn online q 2010 Taylor & Francis DOI: /

3 6 W. Potthast et al. Table I. Mean values and standard deviations of the Shuttle run and subjective perception tests (n ¼ 12). Natural grass Artificial turf 1 Artificial turf 2 Shuttle run time s ^ s ^ ^ 0.25 Perceived grip* 4.3 ^ ^ ^ 1.4 Perceived slip* 5.7 ^ ^ ^ 1.4 *Perception was quantified using a visual analogue scale from Higher values indicate higher grip and slip respectively. Figure 1. Schematic representation of an artificial turf system with elastic layer and two different infill components. Source: Becco, Beccolastic Kunstrasensystem. (FIFA, 2010). To date, the interaction between the player and the different surface systems in soccerspecific situations is not completely understood. Some research has been carried out comparing the incidence of soccer injuries on artificial and natural turf (Ekstrand, Timpka, & Hägglund 2006; Fuller, Randall, Corlette, & Schmalz, 2007a; Fuller, Randall, Corlette, & Schmalz, 2007b; Gaulrapp, Siebert, & Rosemeyer, 1999; Steffen, Andersen, & Bahr, 2007). However, these studies fail to constitute conclusive evidence regarding injury patterns. For example, Ekstrand et al. (2006) found a higher risk of sustaining ankle sprains on artificial turf, while Fuller et al. (2007a) found a lower injury risk for women during matches on artificial turf, with no differences for men. In contrast, Steffen et al. (2007) found a trend (p, 0.06) towards a higher risk of ankle sprains for female players below the age of 17. During training, Fuller et al. (2007b) reported a higher risk of ankle sprains in men on artificial turf, but no differences for women. When players contact the ground at high speed, the risk of skin lesions on artificial turf may be greater than that experienced on grass. Fuller et al. (2007a) reported that men had a greater incidence of skin lesions during matches on artificial turf compared to grass, but that there were no differences for females in match play. These authors also showed no difference in skin lesions during training for males or females (Fuller et al., 2007a), while Ekstrand et al. (2006) did not consider skin lesions in their report. In general, the observational studies on injuries are difficult to compare. This is due to an eventual lack of the definition of an injury, different skill level of observed players, different age categories, and different genders. Despite the limitations of those studies and the lack of standardization and comparability, no study suggests that overall injury incidence is affected by the playing surface. It can be stated that the absolute risk of soccer-specific injuries is not different between artificial and natural grass. It is not yet completely understood whether differences in the distribution of injured sites exist, or if and how gender, skill level, or age affect the etiology of injuries on artificial and natural turf. Observational studies with bigger cohorts include artificial turf systems with different components (e.g. infill, fibres, elastic layer) (c.f. Fuller et al., 2007a; Fuller et al., 2007b). However, they did not differentiate between different systems but embraced all artificial turf systems as a whole. Therefore, it is not clear how modifications in one component may impact the soccer-specific interaction with the player. It is possible that different turf components might also influence soccer-specific injury patterns differently. To date, governing bodies certify turf fields only by pure mechanical tests of surface components (fibres, infill, elastic layer) and completely installed systems. For various activities, it has been shown that the mechanical properties of interfaces influence the response of the human body (Lambson, Barnhill, & Higgins, 1996; Orchard, Seward, & McGivern, 2001; Moritz & Farley, 2004) when interacting with the surface. For example, in running shoes, softer midsoles do not lead to lower ground reaction forces in heel toe running (Clarke, Cooper, & Hamill, 1983; Nigg, Cole, & Brüggemann, 1995; Shorten, 2002). The human response, therefore, cannot be predicted by only analysing the surface properties. This review paper aims to indicate that besides mechanical testing of artificial turf systems, subject testing, i.e. biomechanical and physiological tests, would be helpful to improve the understanding of player surface interaction, and might be necessary (1) to optimize the functionality of artificial turf systems in soccer and (2) to improve the standard of certification of artificial turf systems. Biomechanics A study of 17 high-level German amateur soccer players compared their movements when kicking at the goal on natural and 3G artificial turf pitches (Potthast & Brüggemann, 2009; Potthast & Brüggemann, 2010). The artificial turf systems differed mainly in infill composition (rubber infill vs. sand plus rubber infill), while elastic layer and fibre type were kept very similar. The natural turf was located at the training centre of a German first division soccer

4 club. Using four high-speed video cameras, kicking performance (velocity and accuracy) was determined, as well as the players kicking kinematics, including the whole run-up. The kicking motion and kicking performance were influenced significantly by the interface interventions. Kicking accuracy was worse and ball speed was lower on the artificial pitch with the sand and rubber composition infill compared to the other two pitches. This coincided with changes in the kinematics of the supporting leg, as well as changed deceleration strategies in the last step before ball contact. The pronation of the ankle joint of the supporting leg, occurring in the last step when the kicking leg hit the ball, was significantly higher on the sand and rubber filled pitch (29.9 ^ 18.48) compared to natural grass (20.18 ^ 12) and rubber filled turf (19.8 ^ 14.18). The general approach to the ball (direction and velocity of the run-up) was not influenced by the surface. However, the deceleration before ball contact with the last stance of the supporting leg was significantly lower (Figure 2) on the sand and rubber infill (10.6 ^ 3.2 m/s 2 ) than on natural grass (13.0 ^ 2.5 m/s 2 ) and rubber filled turf (12.3 ^ 3.7 m/s 2 ). In other words, the players reduced their run-up velocity more cautiously on the sand and rubber filled turf. This means that the interface variation changed their motion pattern or their approach strategy significantly. Considering the lower kicking accuracy and ball speed on the same surface, this indicates that the surface variations influenced the player surface interaction in such a way that kicking performance deteriorated. In another study (Verhelst, Verleysen, Degrieck, & De Clercq, 2007; Verhelst, 2010), the kinematics and kinetics of a standing start were analysed and compared on two types of 3G. One surface had a standard SBR infill, whereas the other surface had a TPE (thermoplastic elastomere) infill. Seven male recreational soccer players with the same shoes performed a standing start on both surfaces in the laboratory (Figure 3). The subjects were equipped with eight markers and the tests were filmed with a high speed camera for two-dimensional kinematic analysis. Under the artificial turf, a force plate was installed to measure horizontal and vertical forces. Player surface interaction on different turf systems 7 Figure 2. Mean values and standard deviations of ball speed (X), deceleration of the players centre of mass with the last step (V) and pronation of the stance leg (D). Significant differences to natural grass are indicated with * and to artificial turf with rubber infill with þ(p, 0.05; n ¼ 17). It turned out that the maximum coefficient of friction m max, defined as the maximum ratio of horizontal (F y ) to vertical force (F z ), tended to be higher on SBR than on TPE (0.81 ^ 0.15 vs ^ 0.11). This is confirmed by the finding that the tan (b) tended to be higher on SBR than on TPE (0.64 ^ 0.06 vs ^ 0.1). The tangent of the angle b (angle between connection line toe centre of gravity and the vertical at the moment of m max (Figure 3, middle) indicates the direction of the forces from the body on the surface,and is thus related to the friction ratio m ¼ F y /F z. The knee joint angle g (Figure 3, right) at the moment of toe-off is significantly higher on SBR than on TPE (160.8 ^ 7.78 vs ^ 13.58), which could suggest again a higher grip on SBR, as the leg can be extended more without the risk that the foot starts to slip. A higher knee extension during push-off leads to higher accelerations (Van Ingen, Schenau, de Koning, and de Groot, 1994). The horizontal impulse calculated in the time interval where the vertical component of the GRF is above BW is significantly higher on SBR than on TPE (0.13 ^ 0.02 vs 0.11 ^ 0.02 BW s). This difference is due to higher horizontal forces and a longer contact time on SBR than on TPE (although not significantly). As both effects reinforce each Figure 3. Representation of one subject during sprint starts. The figure shows how the angles a (left), b (middle) and g (right) were determined.

5 8 W. Potthast et al. other, this horizontal impulse shows a significant difference, suggesting a higher grip on SBR compared to TPE. This finding is further affirmed by the fact that the change in COM horizontal velocity during the interval duration BW, Dv y,is higher on SBR than on TPE, although not significantly. In conclusion, the surface variations have a significant influence on player kinetics and kinematics during a standing start movement. In another study, Verhelst (2010) investigated the influence of different surfaces on perception and performance expressed as total running time in a shuttle run. Twelve male soccer players (medium and high level) performed a 10 5 m shuttle run (Lefevre, 1993) requiring multiple 1808 turns. Tests were done on three surfaces: two types of artificial turf and a slightly soggy natural turf field. Both artificial turfs fulfilled the FIFA one or two star requirements for translational and rotational friction. The average total running time was significantly higher (ca. 3%) on natural turf than on artificial turf 1. The differences to artificial turf 2 were not significant. Using a visual analogue scale (VAS) from 0 to 10 (c.f. Fleming, Young, Roberts, Jones, & Dixon, 2005; Grant et al., 1999; Hennig, Valiant, & Liu, 1996; Mündermann, Stefanyshyn, & Nigg, 2001; Mündermann, Nigg, Stefanyshyn, & Humble, 2002) it was quantified how players perceived the slip and grip in the shuttle test (0 ¼ low slip/grip; 10 ¼ much slip/grip). The subjects perceived the highest slip on natural turf, which corresponded to the highest total running time in the performance test (Figure 4). A logical correlation was found between player perception and performance during the shuttle run. A rather poor relationship was found between the results of the pure mechanical linear friction test and both the perceived grip and the shuttle performance. This is confirmed by the findings of Young (2007). In contrast, rotational friction measurement appears to be positively related to perceived grip and shuttle performance (Figure 5). This also supports the findings of Young (2007). These studies about soccer-specific sprint starts and 1808 turning movements show that changes in just one turf component can substantially change the perception, performance, and motion pattern. They also indicate that purely mechanical tests do not necessarily reflect the response of the athlete to surface modifications. It appears that the currently performed mechanical rotational friction measurement is more closely related to perception and performance than the translational friction test. Figure 4. Relationship between perceived slip and total running time on the three different surfaces. Higher values on the visual analogue scale (VAS) indicate more perceived slipping. Higher values on the visual analogue scale (VAS) indicate more perceived slip. For reasons of lucidity standard deviations have been omitted in this figure. They are listed in Table I. Physiology Given the potential for biomechanical variables to be influenced by playing surface, it is likely that physiological responses to soccer play may also be affected by variation in surface. It is established that the physiological stresses during running and jumping are influenced by changes in the surface used (Kerdok, Biewener, McMahon, Weyand, & Herr, 2002; Muramatsu, Fukudome, Miyama, Arimoto, & Kijima, 2006), and evidence from other sports shows that match characteristics and physiological responses can be affected by the type of Figure 5. Relationship between perceived grip and translational (left vertical axis) and rotational (right vertical axis) traction on the three different surfaces. Higher values on the visual analogue scale (VAS) indicate more perceived grip. Note the negative relation between perceived grip and linear traction and the positive relation between perceived grip and rotational traction. For reasons of lucidity standard deviations of the perception tests have been omitted in this figure. They are listed in Table I.

6 surface used (Reilly & Borrie, 1992; Murias, Lanatta, Arcuri, & Laino, 2007). Considering the increased use of artificial soccer pitches and the desire to conserve the characteristics of soccer, it is also important to question whether different playing surfaces will affect match characteristics and their resulting physiological responses. Elite outfield players typically cover distances of 10 to 12 km during a game on a natural grass surface (Andersson, Ekblom, & Krustrup, 2008a; Bradley et al., 2009; Krustrup, Mohr, Ellingsgaard, & Bangsbo 2005; Rampinini, Impellizzeri, Castagna, Coutts, & Wisloff, 2009). Most activity is low to moderate intensity, but this is interspersed with approximately 250 brief periods of high-intensity running and sprinting (Bradley et al., 2009; Mohr, Krustrup, & Bangsbo, 2005). Towards the later stages of a match, the frequency and distance covered in sprinting tends to decrease (Mohr, Krustrup, & Bangsbo, 2003). Throughout matches, players execute a range of movements and skills, involving up to 180 activities on the ball and over 1250 changes in movement type (Andersson et al., 2008a; Bloomfield, Polman, & O Donoghue, 2007). Anecdotal evidence would suggest that variations in playing surface, either between different natural surfaces or between artificial and natural surfaces, affect match characteristics. The perception of players was that technical skills (passing, shooting and controlling the ball) and the physical effort of running without the ball were more difficult on third generation 3G surfaces than on grass (Andersson et al., 2008a). However, only a few studies have performed objective research on this issue. A study commissioned by FIFA (FIFA, 2008) comparing the activities in 100 elite competitive matches showed that the length, direction and accuracy of passes, the effective playing time, the number of on-the-ball activities and possession transitions were similar in play on 3G surfaces and on natural grass. Furthermore, Andersson et al. (2008a) revealed that there was no significant difference in player movement patterns between 3G and natural surfaces. The distance covered in highintensity exercise, sprinting and in total was unaffected by surface, as was the number of changes in activity and the decrease in the distance covered in high-intensity exercise. Although such similarities suggest match characteristics are largely unaltered by the playing surface, the FIFA study did observe trends for a higher incidence of shots, goals and passes on 3G, while a significantly greater frequency of short midfield-to-midfield passes and fewer sliding tackles have been reported on artificial surfaces (Andersson et al., 2008a). It has been suggested that 3G surfaces may elicit a shift towards a more attacking style of play with a higher tempo than on Player surface interaction on different turf systems 9 natural grass (FIFA, 2008), and such changes in the style of play are likely to effect the physiological demands on the players (Reilly, 1997). The unpredictable, intermittent nature of soccer match-play presents significant metabolic and energetic stresses, as evidenced by mean heart rates of approximately 75 87% of maximal heart rate (Ascensao et al., 2008; Krustrup et al., 2005; Krustrup et al., 2006) and mean and peak blood lactate concentrations of approximately 6 and 12 mmol1 or L-1, respectively (Bangsbo et al., 1991; Krustrup et al., 2006; Reilly, 2003). Deteriorations in physical performance (sprinting, jumping, knee extension and flexion) immediately after, and for up to 72 hours following, match-play also imply considerable strain upon neuromuscular parameters, with elevations in creatine kinase and muscle soreness indicating significant intramuscular structural disturbances (Ascensao et al., 2008; Andersson et al., 2008b; Reilly & Rigby, 2002). The inherent variability of soccer makes it difficult to compare these physiological stresses between surfaces from competitive match-play. Preliminary work to study the influence of playing surfaces has been reported by Fletcher et al. (2008), based on a soccer-simulation protocol (Nicholas, Nuttall, & Williams, 2000) using an ordered sequence of walking, jogging and running over 20 m interspersed with 15 m sprints. This study compared the responses to a 20-minute exercise period performed separately on both grass and 3G surfaces and showed that there was no significant difference in physiological response (heart rate and blood lactate) or fatiguing characteristics (deteriorations in 15 m sprint performance) due to playing surface. However, significantly faster 15 m sprint times (1.4%) were recorded on the 3G surface (Fletcher et al., 2008). Such differences in sprint times on artificial surfaces could lead to higher rates of fatigue (Meyers & Barnhill, 2004), although no research exists to provide evidence to suggest that this is the case in soccer activity. A related study has demonstrated that submaximal running at a controlled speed elicits higher heart rate and blood lactate concentration on artificial turf than on grass, but the activities in this study were not representative of soccer (Di Michele, Di Renzo, Ammazzalorso, & Merni, 2009). The soccer-simulation protocol used by Fletcher et al. (2008) adopted a range of exercise intensities while replicating the physiological demands of match-play and some of the movement characteristics. However, the brief duration of activity and the omission of high-speed directional changes, which contribute substantially to energy expenditure (Reilly, 2003), meant that the protocol was not

7 10 W. Potthast et al. truly representative of soccer activity and may not elicit fatigue to the same extent as match-play. Therefore, there are currently no studies which can be used to satisfactorily answer whether the physiological consequences of soccer play are affected by the playing surface. The variable nature of match-play means that only highly extensive studies could be used to address this point from competitive games. Simulations of soccer may provide further evidence about the impact of playing surfaces by matching the physiological demands and approximating the movement characteristics of the sport. Conclusions The published scientific literature indicates that the game s character does not change dramatically when played on third generation artificial turf. Similarly, tactical behaviour seems to change only slightly and the number of injuries appears not to be affected, even though it is not understood whether the injury profile might change with different surfaces. In addition it has to be considered that those studies are based on observations and included different types of third generation artificial soccer turf. Therefore, cause-and-effect relationships cannot be finally deduced. The interaction between the player and different natural grass and artificial turf systems in soccer-specific situations is, basically, not understood. Studies on soccer-specific movements (Potthast & Brüggemann, 2009; Potthast & Brüggemann, 2010; Verhelst et al., 2007; Verhelst, 2010) show that surface changes lead to changes in movement patterns. This is not only true for comparisons between natural grass and artificial turf, but also for comparisons between different third generation turf systems. Furthermore, the differences between artificial turf systems may be greater than the differences between natural grass and artificial turf. Modifications in only one component (e.g. infill composition) can lead to alterations of the motion strategy. In complex soccer-specific movements, such as cuttings or goal kicks, those alterations have the potential to impair performance and eventually to influence the injury profile. The fact that for instance in kicking, the ankle joint of the supporting leg is considerably influenced by changes in the surface, supports the findings of some groups (Ekstrand et al., 2006; Fuller et al., 2007a; Fuller et al., 2007b; Steffen et al., 2007) which indicate that the surface has an effect on the relative number of ankle injuries. However, since those groups did not differentiate between the various artificial turf systems, and since different artificial turf components can have different effects on ankle joint motions, it is still unclear whether the incidence of injury can be attributed to the surface used. The related scientific literature and the results of more current studies indicate clearly that mechanical tests of artificial turf systems do not necessarily reflect how a player would interact with the system. It is apparent that biomechanical tests of soccerspecific movements are necessary to understand how changes in the material properties of the surface impact motor behaviour and musculoskeletal loading. There are clear indications that purely mechanical tests do not sufficiently reflect the response of the human body. This comprises not only sport performance and musculoskeletal loading but also physiological processes. Even though final conclusions cannot be drawn from existing studies, it can be assumed that different surface properties which alter the movement pattern and/or the loading in soccer-specific tasks may modify the related physiological stress. The following figure shows a proposed scheme for a more comprehensive process of functional artificial turf testing and the factors to be considered (Figure 6). A deeper understanding of player surface interaction and how this depends on alterations of surface properties will help to set new standards or to justify existing standards for certification systems of artificial soccer turf. It might also indicate that subject testing, i.e. biomechanical and eventually physiological tests, is necessary to provide suitable certification systems. Producers of artificial turf systems will benefit from better insight into the response of the biological system on surface variations in order to improve the quality of the product, with the final goal of mirrorring natural grass conditions as well as possible. Economically, a more comprehensive knowledge of player surface interaction may help to identify areas where the modification of existing components could lead to reduced costs without compromising the quality of the product. No systematic studies are available that investigate how the different turf components (infill, elastic layer, fibres) influence the characteristics of soccer turf. This is true for purely mechanical tests and especially for biomechanical tests. Further research is necessary to identify soccer-specific motion sequences which are influenced by surface changes. In those motion sequences related crucial time points have to be identified, where the impact of surface changes is reflected and relevant. This would economize biomechanical and physiological tests in both product development and certification processes. If movement behaviour on natural grass is the goal for certification and the development of functional artificial soccer turf, extensive research is necessary in order to establish baselines for certain soccer-specific movements on natural grass.

8 Player surface interaction on different turf systems 11 FOOTBALL GAME Performance Tactical aspects Injury prevention AT COMPOSITION Fibres + attachment Infill Sublayer Dry/wet Temperature FOOTBALL CONTEXT Ecological considerations (C2C) Socio-economical considerations PLAYER SURFACE INTERACTION by means of SOCCER SPECIFIC TESTS including footwear and ball-surface interaction Acknowledgements Gijs De Buyck did an outstanding job in testing players performance and perception when performing soccer-specific movements on different artificial turfs. References MECHANICAL MATERIAL TESTING Andersson, H., Ekblom, B., & Krustrup, P. (2008a). Elite football on artificial turf versus natural grass: Movement patterns, technical standards, and player impressions. Journal of Sports Sciences, 26(2), Andersson, H., Raastad, T., Nilsson, J., Paulsen, G., Garthe, I., & Kadi, F. (2008b). Neuromuscular fatigue and recovery in elite female soccer: Effects of active recovery. Medicine and Science in Sports and Exercise, 40(2), Ascensao, A., Rebelo, A., Oliveirs, E., Franklim, M., Pereira, L., & Magalhae, J. (2008). Biochemical impact of a soccer match analysis of oxidative stress and muscle damage markers throughout recovery. Clinical Biochemistry, 41(10 11), Bangsbo, J., Norregaard, L., & Thorso, F. (1991). Activity profile of competition soccer. Canadian Journal of Sport Sciences, 16(2), Bloomfield, J., Polman, R., & O Donoghue, P. (2007). Physical demands of different positions in FA Premier League soccer. Journal of Sports Science and Medicine, 6, Bradley, P. S., Sheldon, W., Wooster, B., Olsen, P., Boanas, P., & Krustrup, P. (2009). High-intensity running in English FA Premier League soccer matches. Journal of Sports Sciences, 27(2), Clarke, T. E., Cooper, L. B., & Hamill, C. L. (1985). The effect of varied stride rate upon shank deceleration in running. Journal of Sports Sciences, 3, Di Michele, R., Di Renzo, A. M., Ammazzalorso, S., & Merni, F. (2009). Comparison of physiological responses to an incremental running test on treadmill, natural grass, and synthetic turf in young soccer players. Journal of Strength and Conditioning Research, 23(3), TESTS WITH SUBJECTS Biomechanical tests Players perception Physiological tests Game related performance Sprint time Endurance running Agility tests Ball handling Figure 6. Proposed functional artificial turf testing procedure. Ekstrand, J., Timpka, T., & Hägglund, M. (2006). Risk of injury in elite football played on artificial turf versus natural grass: a prospective two-cohort study. British Journal of Sports Medicine, 40, FIFA. (2008). Does the game change on football turf? FIFA Turf Roots Magazine, 3, FIFA. (2010). FIFA quality concept for football turf. Retrieved February 17, 2010, from: afdeveloping/pitchequip/fqc_football_turf_folder_342.pdf. Fleming, P. R., Young, C., Roberts, J. R., Jones, R., & Dixon, N. (2005). Human perceptions of artificial turf surfaces for field hockey. Sports Engineering, 8, Fletcher, N., Nokes, L., Hughes, M. G., Meyers, R., Newcombe, D., Oliver, J., et al., (2008). Physiology effects of playing surface on football activity. FIFA Turf Roots Magazine, 3, Fuller, C. W., Randall, W. D., Corlette, J., & Schmalz, R. (2007a). Comparison of the incidence, nature and cause of injuries sustained on grass and new generation artificial turf by male and female football players. Part 1: match injuries. British Journal of Sports Medicine, 41 Suppl 1, i Fuller, C. W., Randall, W. D., Corlette, J., & Schmalz, R. (2007b). Comparison of the incidence, nature and cause of injuries sustained on grass and new generation artificial turf by male and female football players. Part 2: training injuries. British Journal of Sports Medicine, 41 Suppl 1, i Gaulrapp, H., Siebert, C., & Rosemeyer, B. (1999). Das Verletzungsspektrum und die Überlastungsschäden beim Fußballsport auf Kunstrasen. Sportverl Sportschad, 13, Grant, S., Aitchison, T., Henderson, E., Christie, J., Zare, S., McMurray, J., et al., (1999). A comparison of the reproducibility and the sensitivity to change of Visual Analogue Scales, Borg Scales and Likert Scales in normal subjects during submaximal exercise. CHEST, 116, Hennig, E. M., Valiant, G. A., & Liu, Q. (1996). Biomechanical variables and the perception of cushioning for running in various types of footwear. Journal of Applied Biomechanics, 12,

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