The effect of playing surfaces on performance in tennis. Caroline Martin and Jacques Prioux

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1 The effect of playing surfaces on performance in tennis Caroline Martin and Jacques Prioux Sport Sciences and Physical Education Department, Ecole Normale Supérieure de Cachan, Antenne de Bretagne - M2S Laboratory, UFR APS, University of Rennes 2, Avenue Robert Schuman Bruz, France. DESCRIPTION OF TENNIS PLAYING SURFACES Competitive tennis players are used to playing multiple tournaments on a variety of court surfaces, more so perhaps than any other sport. In 2011, 210 different courts surfaces have been approved by the International Tennis Federation (ITF). The properties of each surface influence the style of the play, the tennis ball rebound and affect the quality of performance. To facilitate the understanding of these properties, the ITF (ITF, 2012) classifies court surfaces into categories according to type (acrylic, artificial clay, artificial grass, asphalt, carpet, clay (CL), concrete, grass, other, see Table 25.1) and court pace rating (CPR), slow (CPR 29), medium-slow (CPR: 30-34), medium (CPR: 35-39), medium-fast (CPR: 40-44), and fast ( 45). (Insert Table 25.1 about here) The characteristics of CPR are determined by two main parameters: their coefficient of friction (COF) and their coefficient of restitution (COR). (1) where COF is the coefficient of friction and COR adj is the temperature adjusted coefficient of restitution. According to the ITF, COF (m.s -1 ) is the ratio of the horizontal force resisting sliding and the vertical force of the ball normal to the surface. (2) 1

2 where V ix is the horizontal inbound velocity (m.s -1 ), V fx is the horizontal outbound velocity (m.s -1 ), V iy is the vertical inbound velocity (m.s -1 ) and COR is the coefficient of restitution. COR (m.s -1 ) is the ratio of the vertical velocity and after the bounce to that before impact. (3) where V fy is the vertical outbound velocity (m.s -1 ) and V iy is the vertical inbound velocity (m.s -1 ). For a 29 m.s -1 groundstroke with a standard type 2 tennis ball on a fast court with pace rating of 60, the ball will reach the other baseline with a speed about m.s -1, or with 53 per cent of its original speed. On a medium-slow court with a pace rating averaging 30, the ball will arrive at the baseline with a speed of m.s -1, or 45 per cent of its original speed (Brody, 2003). According to Brody (2003), players should increase their racket head velocity by 25 per cent to maintain the same ball speed at the opposite baseline for medium slow courts with pace value of 30 than for fast courts (pace value = 60). Hard courts (H), CL and grass are the most common surfaces on which professional and leisure tennis are played today (Miller, 2006). In 2006, six tournaments of the Association of Tennis Professionals world tour were played on grass, 30 on H and 25 on CL. During the same year, four tournaments of the Women Tennis Association professional world tour were played on grass, 37 on H and 15 on CL. In the professional circuit, the four Grand Slam tournaments are now played on these different surfaces. Indeed, the US Open moved from the grass courts to the Decoturf (H) courts in 1978 and the Australian Open moved from the grass surface to the Rebound ace (H) surface in Wimbledon remains a grass court tournament and the French Open is still played on the CL of Roland Garros. Consequently, the characteristics of the CL, grass and H surfaces are exposed in the following section. Grass court 2

3 According to Miller (2006) and Brody (2003), the COR of grass court is low (0.77) inducing a lower height of the vertical bounce of the tennis ball than on other surfaces. This reduces the time between the first and the second bounce, which players can also perceive as a fast surface with a CPR value of 46. On grass court, there is a less loss of horizontal velocity during the ball rebound since the COF of this surface is low. As a consequence, the player will have less time to get to the ball and prepare its shot than on CL court (Brody, 2003). Clay court CL court is considered as a slow surface (CPR = 23), characterized by higher COR (0.86) and COF (>0.71) than faster surfaces. This results in a high and relative gentle bounce and slows down the ball. On CL, the ball may pick up bits of CL or moisture and become heavier. This phenomenon slows down more the game on CL courts because a heavier ball comes off the racket with slightly less speed (Brody, 2003). Hard court H courts, like Rebound Ace in the Australian Open and Decoturf in the US Open, are usually considered as medium surfaces, with a CPR value between 35 and 39, COF ranging from 0.56 to 0.70 and COR between 0.79 and THE PHYSIOLOGICAL DEMANDS INVOLVED IN TENNIS MATCHES Tennis is a sport that requires a mixture of complex skills (technical, tactical, psychological) and physical attributes (speed, agility, endurance, strength, balance, flexibility, anticipation, power) (Kovacs, 2007). Match play is defined by intermittent exercise: short bout of high intensity (< 10 seconds) are interrupted by short recovery bouts (10-20 seconds) and periods of longer duration ( seconds). During this time, a player runs about 3m per stroke 3

4 (Parsons and Jones, 1998), changes direction four times by point and completes explosive efforts during a match (Deutsch et al., 1998). According to Kovacs (2007), utilizing the correct energy system during training will improve performance during matches. As a consequence, it is important to know the involvement of energy systems during tennis matches. As tennis activity is characterized by periods of high-intensity exercise (powerful serves and groundstrokes, rapid changes of direction, explosive nature of the displacements ) disrupted by periods of low intensity exercise of various duration (active recovery between points or sitting periods during changeovers), one may argued to classify it as anaerobic predominant activity requiring high levels of aerobic conditioning to aid in recovery between points and matches (Kovacs, 2006). Different studies have used portable gas analyzers to have an oversight of mean oxygen uptake ( O 2 ) during tennis matches (see Table 25.2). It has been reported that O 2 levels during matches vary from 23.3 ± 3.0 ml.min -1.kg -1 for recreational veterans (Fernandez-Fernandez et al., 2009) to 40.3 ± 5.7 ml. min -1. kg -1 for club male players (Girard and Millet, 2004). This corresponds to about 60 per cent of O 2max, with values ranging from 46 per cent to 80 per cent of O 2max (see Table 25.2). During matches, mean O 2 reached 60 per cent of the O 2max for 80 per cent of the duration of the match. During the points, O 2 varied from 70 to 95 per cent of O 2max and decreased rapidly during the changes of side (Dansou et al., 2001). (Insert Table 25.2 about here) Regarding the heart rate (HR), the literature shows that HR is measured as indices to evaluate the intensity and the psychological stress associated during practice (Fernandez- Fernandez et al., 2008). It has been reported that mean HR values during matches vary from 135 to 161 bpm (see Table 25.2) rising to bpm during long and intense rallies (Girard and Millet, 2004; Smekal et al., 2001). The mean percentage of maximum heart rate 4

5 (HRmax) during matches has been reported to approximate 86 per cent and to be not significantly different from the 83 per cent measured during recovery (excluding the rest periods between points and games) (Bergeron et al.,1991). However, care should be taken when looking at the results of mean HR values as they do not accurately represent the intermittent nature of the tennis match (Fernandez-Fernandez et al., 2009; Kovacs, 2007). Indeed, HR values vary continuously during a match due to the continual stop-start movements and intermittent nature of the sport (Bergeron et al., 1991; Dansou et al., 2001) (Figure 25.1). It has been reported that players spent about 13 per cent of match duration at intensities higher than 90 per cent of HRmax. Moreover, the serving situation influences HR during male and female matches: mean HR values were significantly higher when serving than when receiving (Fernandez-Fernandez et al., 2007; Mendez-Villanueva et al., 2007). This result could be explained by the higher psychological stress and sympathetic activity related to the importance to win the service games (Fernandez-Fernandez et al., 2009). (Insert Figure 25.1 about here) Finally, in the scientific literature on tennis, the blood lactate concentration ([La]) is measured as indices to evaluate the intensity of tennis match play and to obtain an oversight of the energy production from glycolytic processes (Fernandez-Fernandez et al., 2009). Mean [La] values during matches remain low (from 1.16 to 5.7 mmol.l -1 ) (see Table 25.2). Indeed, the periods of rest during match seem sufficient to allow players to reduce the metabolism products (Bergeron et al., 1991; Martin et al., 2011). [La] values can rise to 8 mmol.l -1 during long and intense rallies (Martin et al., 2011), suggesting an increased participation of glycolytic processes to energy supply. When [La] exceed 7-8 mmol.l -1, technical and tactical performance decreases (Ferrauti et al., 2001a; 2001b). So, it is important to prepare players properly to deal with these high intensity situations and to use optimally resting times. The discrepancies between studies concerning mean [La] values are probably the results of 5

6 differences in the characteristics of the subjects and the experimental design (number and time of blood taking). However, care should be taken when looking at the results because [La] values only reflect the level of activity during the few minutes before sampling (Martin et al., 2011). (Insert Table 25.3 about here) THE INFLUENCE OF TENNIS PLAYING SURFACE ON MATCHES CHARACTERISTICS As we have seen previously, the court surface influences the tennis ball rebound and the ball speed (Brody, 2003; Miller, 2006) and as a consequence the match s technical characteristics - that is, its effective playing time (EPT), effective resting time (ERT), total match duration (MD), mean rally duration (MRD), resting time between points (RT), number of strokes per rally (SR) and distance ran per point (DRP) (Table 25.3). The EPT, defined as the duration during which the ball is really in play is, on average, significantly longer on CL (20-30 per cent of total match duration) than on faster surfaces, such as H courts (10-15 per cent of total match duration) (Table 25.3). O Donoghue and Ingram (2001) conducted a notational analysis of singles events at all four Grand Slam tournaments between 1997 and 1999 to determine the influence of the surface on tennis matches. Rallies of 6.3 ± 1.8 s at the Australian Open (H), 7.7 ± 1.7 s at the French Open (CL), 4.3 ± 1.6 s at Wimbledon (grass) and 5.8 ± 1.9 s at the US Open (H) were recorded. Rallies were significantly longer at the French Open than at any other tournament and significantly shorter at Wimbledon than at any other tournament. In the same way, it has been shown that SR and DRP are significantly higher on CL than on H. All these results can be explained by the tactical behavior used by players according to the court surface. For example, a more aggressive and attacking game is associated with faster surface such as grass. This type of study has been repeated for a more 6

7 recent period. Indeed, Brown and O Donoghue (2008) have conducted a notational analysis of singles events at all four Grand Slam tournaments during They revealed that the difference between rally durations at the French Open (7.3 s) and Wimbledon (3.8 s) in 1997 to 1999 has decreased in 2007 (7.6 s and 5.4 s respectively). Moreover, rallies in men's singles have increased in duration at all four tournaments since There was a lower percentage of service points (aces, double faults, serve winners and return winners) in men s singles at each tournament in 2007 than reported by O Donoghue and Ingram (2001). These data reflect two evolution points in elite competitive tennis matches. Firstly, they can be explained by the introduction of new balls by the ITF to reduce the variation between different surfaces. In 2006, the ITF decided to use type 1 balls on the slowest surfaces and type 3 ball on the fastest surface. Because the type 3 ball is six to eight per cent bigger than the standard type 2, it generates greater air resistance, resulting in greater air deceleration before the rebound (Miller, 2006). Secondly, one may argue that players are fitter and show better technical abilities currently than during the 1990s, allowing them to reach more balls and increase the duration of rallies (Brown and O Donoghue, 2008). THE INFLUENCE OF TENNIS PLAYING SURFACE ON MATCHES CHARACTERISTICS AND PHYSIOLOGICAL PARAMETERS Studies analyzed the effect of court surfaces on the match s technical characteristics in relation with the player s physiological responses during simulated tennis competition (Girard and Millet, 2004; Martin et al., 2011; Murias et al., 2007). They found a relationship between the changes in match characteristics induced by court surface and physiological responses. Court surface influences tennis match characteristics that are probably responsible for the higher mean HR and [La] values measured on CL than on H, suggesting an overall higher physiological demand on that surface (Martin et al., 2011; Murias et al., 2007; Reid et 7

8 al., 2012). The fact that, on H, the rallies are less long and less intense than on CL could be a factor responsible for higher [La] values on CL. Girard and Millet (2004) found high correlations between the percentage of HRmax, duration of rallies and shots played consecutively on CL and H courts (see Figure 25.2). HR increases when subjects hit more consecutive shots and play longer rallies. In the same way, Fernandez-Fernandez et al. (2007) found a significant positive relationship between rally duration, strokes per rally, changes of direction and [La] and HR responses, with stronger correlations when the players were serving on CL. Concerning O 2, Girard and Millet (2004) reported higher mean O 2 values on CL than on H. According to Murias et al. (2007), mean per cent of O 2max was not altered by the playing surface. These results are suggestive of an increased physiological demand on CL. Fernandez-Fernandez et al. (2010) have examined how the training surface (CL or carpet) affects the characteristics (ball velocity, running pressure, running volume, physiological responses) of a training session. They reported no significant difference of the court surface on any variables analyzed. (Insert Figure 25.2 about here) THE INFLUENCE OF TENNIS PLAYING SURFACE ON FATIGUE In tennis, the fatigue may be related to a prolonged or high-intensity physical exertion (Hornery et al., 2007). For these authors, fatigue can be defined as an acute impairment of exercise performance, which ultimately leads to the incapacity to produce maximal force output and/or control motor function. In tennis, fatigue may be resulted in a sequence of long and intense points. To our knowledge, only one study has focused on the effect of the playing surface properties on the development of neuromuscular fatigue in tennis (Fabre et al., 2012). In this study, ten subjects played randomly two tennis matches on H-court and CL-court for an effective playing duration of 45 minutes, corresponding approximately to a three-hour 8

9 game. Before and after each match, the maximal voluntary contraction force of the plantar flexors, the maximal voluntary activation level, the maximal compound muscle action characteristics and the electromyographic activity were determined on the soleus and lateralis gastrocnemius muscles. Any significant difference between playing surfaces was observed in this study. These results suggest that the ground surface properties influence neither the extent nor the origin of neuromuscular fatigue in tennis. THE INFLUENCE OF TENNIS PLAYING SURFACES ON INJURIES Most epidemiological studies in tennis players have shown that overuse injuries are very common in all competitive levels (Jayanthi et al., 2005; Pluim et al., 2006). Among these injuries, it has been reported that lower limb problems are nearly equal or exceed upper limb pains (Pluim et al., 2006). This phenomenon can be explained by the nature of the tennis game that involves quick, intense and repeated start-stop movements, changes in direction, running and sliding side-to-side (Kovacs, 2006). However, injury rates depend not only of the nature of the sport but are also caused by a lot of risk factors. Indeed, in sport injury, risk factors are often classified into two main categories: intrinsic athlete-related factors (age, gender, skill level, somatotype, biomechanics, conditioning, maturational stage ) and extrinsic environmental factors (weather, rules, equipment, floor surfaces ) (Taimela et al., 1990; Van Mechelen et al.,1992). As an extrinsic environmental factor, the court surface has been shown to have an influence on the injury pattern of tennis players (Dragoo and Braun, 2010; Nigg and Segesser, 1988; Nigg and Yeadon, 1987). A study of incomplete matches in Grand Slam professional tennis tournaments from 1978 to 2005 reported the following results: fewer incomplete matches on grass courts (2.0 per cent for men in Wimbledon between 1995 and 2004), higher rates of incomplete matches on Australian Open H courts (1.9 per cent) than on other surfaces (0.6 per cent) in Wimbledon and Roland Garros, 0.8 at 9

10 the US Open) for women and a higher rate of incomplete matches on US Open H courts for men (4.3 per cent between 1995 and 2004) than on other surfaces (3.1 per cent in Australian Open and 3.6 per cent in Roland Garros) (Cross, 2006). Breznik and Batagelj (2012) clearly confirmed the influence of the surface type, with the proportion of retired matches being higher on H and CL courts compared to grass and carpet surfaces. Moreover, it has been reported that senior players who spent their careers on CL rather than on H surfaces had lower rates of knee problems (Kulund et al., 1979). Bastholt (2000) has examined injury rates in professional male tennis players for three years on CL, H, grass and carpet courts. According to the results, injury treatment during matches was required significantly more often on H than on CL courts. In the same way, Nigg and Denoth (1980) used a retrospective design study over 3 seasons to question 1003 tennis players to study the relationship between tennis injuries and court surfaces. They showed that back, knee and ankle joints were the locations the most frequently injured and that athletes playing on surfaces allowed sliding, as CL courts, were related to significant less pain and injury than athletes playing on surfaces which did not allow sliding (asphalt, synthetic surface).in the literature, possible causes related to court surfaces for such differences have been suggested (Nigg and Segesser, 1988) and will be exposed in the following sections. Ground reaction forces Dixon and Stiles (2003) found no significant difference in vertical impact force or peak inshoe heel pressures across surfaces typically used in tennis when running at a relaxed pace. However, we can suppose that the task in this study ( running at a relaxed pace ) was not sufficient to simulate the complex tennis activity and movements that would have revealed impact force differences between court surfaces. Tiegermann (1983) compared the ground reaction forces and the EMG activation of the soleus and peroneus longus in fast sideways 10

11 movements on carpet and CL courts. The ground reaction forces and the EMG activity were significantly higher on carpet than on CL. Moreover, Girard et al. (2007) compared in shoeloading patterns during two frequent tennis-specific movements (serve and volley, baseline play) performed on two court surfaces (CL and H) to identify the main loading patterns and locations on the anatomical structures of the foot. Regarding the whole foot, mean force was significantly lower on CL (614 ± 73 N) than on H court (717 ± 133 N) (p<0.05). These results mean that the magnitude of external forces induced by the court surface on the musculoskeletal system is less important. This phenomenon could explain why epidemiological studies reported lower injury rates on CL than on H courts. Furthermore, higher loadings in hallux and lesser toes area were measured on H court than on CL (Girard et al., 2007). Conversely, the CL condition was characterized by higher loadings and relative loadings on medial and lateral midfoot (see Figure 25.3). As a consequence, it was concluded that the type of court surface influences plantar loading at specific foot regions and, as a consequence, differently affects the aetiology of surface-related injuries (Girard et al., 2007). (Insert Figure 25.3 about here) Cushioning / stiffness Stiles and Dixon (2006) have evaluated the influence of court surfaces with different cushioning values on the ground reaction forces during tennis running forehand trials. They reported that the surface with the lowest mechanical cushioning induced the lowest vertical force magnitude. However, according to Nigg and Yeadon (1987), the cushioning of a tennis court is less important for load reduction than reduction of frictional forces. Indeed, they showed that the surfaces synthetic sand and synthetic turf have the same stiffness. However, the number of people complaining about pain is higher while playing on synthetic turf than on synthetic clay. This result could be explained by the only difference between 11

12 these two surfaces. Indeed, the synthetic sand has an additional loose layer of granules on its top that allows tennis players to slide. Consequently, the stiffness of the surface seems less important than the frictional properties for preventing tennis injuries (Nigg and Yeadon, 1987). Frictional properties Frictional properties of the tennis shoe-surface interface are a factor that could explain pain/injury frequency and severity (Nigg and Yeadon, 1987). Translational friction determines how much horizontal force will be needed to cause the shoe to slide over the surface. CL courts show a lower coefficient of translation friction than H courts. As a consequence, it has been suggested that playing on CL could produce lower frictional resistance and will decrease the loadings at the joints, which reduce the risk of lower extremity injuries (Girard et al., 2007). Rotational friction determines how much force must be applied as a moment of force to cause the shoe to pivot on the surface. The maximum torque is often measured by researchers comparing various surfaces and shoe combinations to evaluate the rotational friction of the combination. This value corresponds to the maximum torque to produce a shoe rotation on the given surface (Frederick, 1993). It has been reported that surfaces with higher rotational friction demonstrate greater peak torques during pivoting. Conversely, surfaces with lower rotational friction show lower peak torques (Frederick, 1993). For example, executing a guided rotation of 180 degrees on CL court would result in a peak torque of about 20 Nm (Michel, 1978). Performing the same movement on an grass court and on an asphalt court, the maneuver would respectively produce a peak torque of about 25 Nm and 30 Nm (Michel, 1978). High rotational friction on sport surfaces has been shown to cause an increased incidence of knee and ankle injuries (Nigg and Denoth, 1980). 12

13 THE INFLUENCE OF TENNIS PLAYING SURFACES ON STRATEGY O Donoghue and Ingram (2001) evaluated the effect of tennis court surfaces on the strategies of elite players in single events at Grand Slam Tournaments between 1997 and According to their results, there were significantly more aces played at Wimbledon than at Roland Garros and significantly more serve winners at Wimbledon than at Roland Garros and at the Australian Open. This result could be explained by the court surface. Indeed, CL courts in Roland Garros induce slower and higher ball bounce, providing the receiver with the opportunity of returning more serves than on faster surfaces such as grass in Wimbledon. Moreover, the players approached the net significantly more at Wimbledon and the US Open than at Roland Garros. Conversely, the proportion of baseline rallies played at Roland Garros (51.9 ± 14.3 per cent of points) was significantly higher than at the Australian Open (46.6 ± 12.5 per cent), Wimbledon (19.7 ± 19.4 per cent) and the US Open (35.4 ± 19.5 per cent). These results suggest that, on slow surfaces (such CL), the tennis players have difficulty to hit effective approach shots that pressurize their opponent to reduce the risks of successful passing shots or lobs. As a consequence, they prefer to hit baseline strokes. Furthermore, no significant difference was reported between the four tournaments in the percentage of points won at the net and in the percentage of points won when players remained at the baseline by the serving player or the receiving player. In the same way, Barnett and Pollard (2007) analyzed various match statistics for men and women during Grand Slams (see Table 25.4). Progressing from left to right in both tables, their results report an increase in the winning percentage on first serve, an increase in the serving points won, an increase in aces and an increase in net approaches. As a consequence, the authors assumed that there was a fundamental ordering of court speeds between Grand Slams: grass, DecoTurf, Rebound Ace, CL. (Insert Table 25.4 about here) 13

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