Analysis of motor and technical activities of professional soccer players of the UEFA Europa League

Transcription

1 International Journal of Performance Analysis in Sport 2014, 14, Analysis of motor and technical activities of professional soccer players of the UEFA Europa League Marcin Andrzejewski 1,3, Jan Chmura 2 and Beata Pluta 1 1 Faculty of Methodology and Recreation, University School of Physical Education, Poznan,ul. Królowej Jadwigi 27/ Poznan, Poland 2 Faculty of Players' Motor Activity, University School of Physical Education, Wrocław, ul. Paderewskiego Wrocław, Poland 3 KKS Lech Poznań S.A. Football Club, Poznań, ul. Bułgarska 5/ Poznań, Poland Abstract The aim of this study was a detailed physical and technical activities analysis of professional soccer players. The studied match performance variables included physical activity and technical actions. The study included 147 soccer players participating in 10 matches of the and Europa League seasons. Physical and technical variables were analyzed according to players positions on the field. The study was performed using the Amisco Pro (version ). The statistical analysis revealed that the total distances covered by studied players ranged from 10,335 m to 11,760 m, with the total sprinting distance ranged from 167 m to 346 m. While in ball possession, the forwards and external midfielders covered a 10-fold longer total sprinting distance than the central defenders (p < 0.05). The technical analysis showed that the players retained ball possession between 36.4 s and 64.9 s per match, and they had no more than 2.3 ball touches per individual possession. More specifically, the central defenders performed successful passes at 76.7%, and forwards at 69.7%. In conclusion, elite soccer players feature the ability to repeat high-intensity actions, while losing a certain number of ball possessions, and to perform technical actions quickly during matches. Keywords: motion analysis, sprinting, playing positions, technique 1. Introduction Association football is team sport featuring an acyclical, intermittent and non-repeatable game play due to its changing and unpredictable course (Nicholas et.al., 2000; Wragg et al., 504

2 2000). The constant increase in popularity and evolution of soccer creates the need for instant recognition and analysis of players activities and systematic assessment of game characteristics. The anticipation of future results on the basis of available data is an important aim of all match analyses. The analyzed data is used for developing gameplay models of players, teams, or for proposing specific match solutions. The observed repeatability of various indices allows predicting future developments and setting trends (Borrie et al., 2002). Quantitative analysis of team and players motor activities is one of the most important components of the modern training process. Obtaining accurate positional and movement information about players is of interest to coaches because of the potential to relate performance to tactics and to assist in the design of better training programs (Figueroa et al., 2006; Barris and Button, 2008; Carling et al., 2009). The data concerning the total distance traveled at different intensities, number of sprints, mean sprinting distance or the number of ball touches per individual possession is used to identify key elements of performance according to different playing positions on the field (Dellal et al., 2009). Over the last decade technological developments in game analysis have been based on advanced motion analysis systems used currently in professional soccer (Barris and Button, 2008; Carling et al., 2008). Computerized analysis has progressed from a simple analysis of players actions such as shots, passes, dribbles, to the development of so-called tracking, i.e. recording and reproducing players movements as simulations in two dimensions (Carling et al., 2009). Nowadays, a semi-automated motion system can be applied for planning tactics and strategies, measuring team organization, providing kinematic feedback, and objective measures of intervention effectiveness in team sports (Barris and Button, 2008). This system permits a precise assessment of physical and technical activities of all players on the pitch and a comparison of their characteristics, while in offensive and defensive play (Di Salvo et al., 2006). The data produced by player tracking systems could be used to improve tactical decision making, direct technical development strategies and prescribe modifications in strength and conditioning training programmes (Glazier, 2010). The individualization of training programs concerning both technical and tactical activities as well as physical loads must account for the player s position on the field. Studies (Bangsbo et al., 1991; Di Salvo et al., 2007; Andrzejewski et al., 2012) show, for example, that midfielders cover much longer distances than defenders and forwards. However, individual differences in the distance covered are not just related to the division into basic traditional team positions of defenders, midfielders and forwards. For each playing position, there may be a significant variation in the physical demands, depending on the tactical role and the physical capacity of the players. For example, Barros et al. (2007) and Di Salvo et al. (2007) showed that in professional Brazilian and European soccer, external defenders ran significantly longer distances than central defenders. Again, marked differences in the intensity of various running activities exist across the various playing positions. A detailed analysis of English Premier League players showed that the playing 505

3 position (defender, midfielder and forward) had a significant influence on players sprinting distances (Bloomfield et al., 2007). Analysis of work rate categories also suggests that training and fitness testing should be tailored specifically to positional groups (e.g. central and external midfielders), rather than simply differentiating between forwards, midfielders and defenders, because each positional group has its own unique physical demands. Findings from a study of 147 professional European players showed that central defenders sprinted over significantly shorter distances than external defenders (Andrzejewski et al., 2013). A large-scale study of professional Spanish soccer players reported a significant difference in the total distance sprinted by external midfielders compared with central midfielders (Zubillaga et al., 2007). This research again demonstrates the need for a criterion model in order to tailor training programmes and strategies to suit the particular needs of individual playing positions. Research dividing players high-intensity efforts into defensive and offensive plays would be pertinent to determine whether positional role determines the physical contribution of players according to whether their teams are in ball possession or not. Motion analysis in professional soccer must therefore account for technical-tactical and physical demands imposed upon players during the game. So far, studies on technicaltactical activities in combination with physical activities of elite soccer players have mostly focused on analyses of matches from English, Spanish, Italian and French national leagues (Rampinini et al., 2009; Carling, 2010; Dellal et al., 2010; Carling and Dupont, 2011; Dellal et al., 2011). No similar studies, however, have been performed using match analyses from the UEFA Europa League matches. The present research involved technical and physical analyses of activities of professional soccer players participating in the UEFA Europa League matches accounting for the players different positions on the pitch. 2. Methods 2.1. Experimental Approach to the Problem An objective analysis of total covered distance by professional soccer players, including sprinting and high-speed distances, was carried out using a state-of-the-art match analysis computer system Amisco Pro. The main research assumption was that a player s position on the field determined the total distance, sprinting distance and high-speed distance covered during the game both in offensive and defensive play as well as the performance of selected technical-tactical actions: percentage of successful passes, total duration and number of individual ball possessions and the number of ball touches per individual possession. It was assumed that there were statistically significant differences between the player s position and variables in the study. 506

4 2.2. Players The study sample comprised 147 players in 5 outfield positions: central defenders (CD, n = 39), external defenders (ED, n = 35), central midfielders (CM, n = 35), external midfielders (EM, n = 20) and forwards (F, n = 18). Ten Europa League matches from the and seasons were recorded. The analysis involved physical and technical activities of the players participating in the entire match, excluding the goalkeepers. Five of the examined matches ended in a draw, there matches were won by the home team, whereas two matches were won by the visiting team. The authors received written consent from the authorities of the KKS Lech Poznan football club to use statistical data provided by the club. The players were informed about all experimental procedures, and informed consent was obtained from them to participate in the study. To ensure club and players confidentiality, all performance data were anonymous. The study was conducted in compliance with the Declaration of Helsinki, and was approved by the local ethics committee (No. 339/02). The study protocol was also approved by the Board of Ethics of the University School of Physical Education in Poznan Procedures The study used one of the latest and most versatile match performance analysis computer systems, Amisco Pro (version 1.0.2, Nice, France). This multiple-camera system tracked the movements of each player over the course of the matches. Eight stable cameras were positioned at the Municipal Stadium in Poznań, Poland and subsequently calibrated and synchronized. Signals and angles obtained by the encoders were sequentially converted into digital data and recorded on six computers for post-game analysis. The movements of each player over the course of matches were tracked using a sampling rate of 25 Hz. Operators experienced in video match-analysis simultaneously coded each player s action with the ball. Physical and technical performance from the raw data file was determined automatically by computerized analysis of player movements and actions using matchanalysis software (AMISCO Viewer, Sport-Universal, Nice, France). The working, accuracy, and reliability of the AMISCO Pro system in measuring player s movements and coding game events in professional soccer competition have been described in more detail elsewhere (Di Salvo et al., 2007; Zubillaga et al., 2007; Carling et al., 2008; Zubillaga et al., 2008). The physical parameters recorded were: the total distance covered, total distance covered while sprinting ( 24km h -1 ), and total distance covered in high-speed intensity runs (21-24km h -1 ). These speed categories are similar to those used in other studies using the same analysis system (Di Salvo et al., 2007; Carling and Bloomfield, 2010; Dellal et al., 2010; Andrzejewski et al., 2012). The physical efforts of players were calculated according to whether their team was in or not in possession of the ball, i.e. in offensive or defensive play. 507

5 The examined technical parameters included the percentage of successful passes, total duration and number of individual ball possessions and the number of ball touches per individual possession. 2.4 Statistical Analysis All values were expressed as mean values ± standard deviation (mean ± SD) and median, interquartile range. The normal distribution of data was checked using the Shapiro-Wilk test. A two-way analysis of variance (ANOVA) with repeated measures was used to compare the distance covered according to two factors: playing positions with five levels (CD, ED, CM, EM and F) and the distances covered at two threshold intensities with two levels (21-24km h -1 and > 24km h -1 ). With regard to the technical performance, a one-way ANOVA was used to compare the technical aspects according to playing position with five levels (CD, ED, CM, EM and F). The significant main effects of each factor were followed up with the post hoc Bonferroni-corrected multiple comparisons test. The level of significance was set at p < The high-speed running distance (21-24km h -1 ) covered by players in five different positions on the field, in defensive play and in offensive play, revealed a moderate absolute agreement of ricc = A similar value was found in the analysis of total sprinting distance ( 24 km h -1 ) covered by players in defensive and offensive play (ricc = ). All statistical analyses were carried out using the STATISTICA 10 software package. 3. Results 3.1 Physical performance Total distance covered In terms of total distance covered by soccer players under study, statistically significant differences were found between all playing positions (p < 0.05) (Tab.1). Central midfielders covered the longest distance in comparison with all other playing positions; however, significant differences were noted between central midfielders and central defenders, central midfielders and forwards, and central midfielders and central defenders (p < 0.05). Significant differences were also observed between external defenders and central defenders, and between external midfielders and central defenders (p < 0.05). Table 1 shows, that in offensive play the longest total distance was covered by forwards and external midfielders when compared with external defenders and central defenders (p < 0.05). Significant differences were also found between central midfielders and central defenders. The distance covered in defensive play was the longest by central midfielders, followed by external defenders and external midfielders; and there was a statistically significant difference with forwards (p < 0.05), who covered the shortest distance without ball possession in comparison to all other playing positions. 508

6 Table 1. Physical and technical characteristics of match-play in professional soccer players in the Europe League (mean ± SD). ED (n = 35) CD (n = 39) CM (n = 35) EM (n = 20) F (n = 18) Follow-up Tests (Bonferroni) Total distance covered [m] (790) (470) (797) (690) (648) CM > ED = F = CD < EM, ED > CD* Total distance covered in possession [m] 3455 (587) 3014 (495) 3828 (618) 4076 (460) 4137 (496) (F = EM) > ED = CD < CM* Total distance covered not in possession [m] 4000 (630) 3839 (576) 4265 (767) 3906 (721) 3213 (662) (CM = ED = EM) > F* Total distance covered in high-speed running (HSR) [m] 325 (93) 214 (95) 316 (113) 384 (109) 331 (88) (EM = F = ED = CM) > CD* Total HSR distance in possession [m] 96 (66) 25 (22) 119 (81) 218 (96) 227 (91) (F = EM > CM = ED) > CD* Total HSR distance not in possession [m] 206 (69) 169 (72) 179 (95) 146 (77) 85 (58) ED > EM = F < (CM = CD)* Percentage of the total distance covered in HSR 2.9 (0.7) 2.1 (0.9) 2.7 (0.9) 3.2 (0.8) 3.0 (0.8) (EM = F = ED) > CD* Total sprint distance covered [m] 264 (121) 185 (82) 167 (87) 313 (122) 346 (129) (F = EM = ED) > (CD = CM)* Total sprint distance covered in possession [m] 109 (92) 20 (29) 65 (75) 219 (123) 244 (86) (F = EM) > (CM = CD), F > ED > CD* Total sprint distance covered not in possession [m] 148 (68) 152 (74) 96 (61) 91 (51) 90 (73) (CD = ED) > (CM = EM = F)* Percentage of total distance covered in sprinting 2.4 (1.0) 1.8 (0.7) 1.4 (0.7) 2.7 (1.1) 3.1 (1.1) (F = EM) > (CD = CM), ED > CM* * Significant difference between playing positions (p < 0.05). 509

7 High-speed running The analysis of the total distance covered while running at a high speed (21-24km h -1 ) revealed similar distances covered by external midfielders, forwards, external defenders and central midfielders, and higher distances in comparison with central defenders (p < 0.05). Table 1 shows that the mean percentage of high-speed running was between 2.1% and 3.2% of total covered distance. External midfielders, forwards and external defenders covered the longest high-speed running distance (in %). That was statistically significantly longer than central defenders (p < 0.05). In offensive play, central defenders covered decidedly the shortest high-speed running distance in comparison with the other playing positions (p < 0.05). Forwards and external midfielders covered similar distances, longer than those of central midfielders and external defenders (p < 0.05) (Table 1). In defensive play, external defenders covered the longest high-speed running distance significantly differing from external midfielders and forwards (p < 0.05). Similar results were obtained by central midfielders and central defenders, significantly different from distances by forwards (p < 0.05) (Table 1). The analysis of total high-speed running (21-24km h -1 ) distance covered by each positional group showed that defenders (central and external) ran statistically significantly longer distances in defensive play than in offensive play (p < 0.05). On the other hand, the forwards ran longer high-speed distances in offensive play than in defensive play (p < 0.05) (Figure 1). 510

8 Distance [m] 350 F=28,27 p<0, * * 100 * 50 0 ED CD CM EM F Figure 1. High-speed running (21-24km h -1 ) across playing positions in the Europe League according to team ball possession: in possession; not in ball possession. * Significantly longer total distance covered in high-speed running when their team was in ball possession and not in ball possession (p < 0.05). Sprinting activity The statistical analysis revealed that the mean total sprinting ( 24 km h -1 ) distance run by all studied players (n = 147) was 237 ± 123 m. Statistically significant differences were found between sprinting distances covered by all players on the pitch (p < 0.05), i.e. between forwards, external midfielders and external defenders, and central defenders and central midfielders (p < 0.05). According to playing position, the mean percentage of sprinting activity in the entire player s running time ranged between 1.4% and 3.1% of total covered distance. Statistically significant differences were found between all playing positions (p < 0.05), i.e. between forwards and external midfielders, and central defenders and central midfielders (p < 0.05). The external defenders covered a longer mean sprinting distance than the central midfielders (p < 0.05) (Table 1). The analysis of sprinting distance ( 24 km h -1 ) covered in offensive play showed that the most active in sprinting were the forwards and external midfielders as compared with central midfielders and central defenders (p < 0.05). Moreover, the forwards covered a 511

9 Distance [m] significantly longer sprinting distance in offensive play than external defenders (p < 0.05). In fact, the sprinting distance covered by the forwards and external midfielders in offensive play was more than 10 times longer than the distance run by central defenders. In defensive play, the most similar and the longest sprinting distance was run by central defenders and external defenders, followed by the central midfielders, external midfielders and forwards (p < 0.05) (Table 1). Considering the total sprinting distance ( 24 km h -1 ) covered by players in different pitch positions, the central defenders ran significantly longer in defensive play than in offensive play (p < 0.05). On the other hand, the forwards and midfielders, while in ball possession, covered a longer sprinting distance than in defensive play (p < 0.05) (Fig. 2) F=32,61 p<0, * ED CD CM EM F * * Figure 2. Sprinting ( 24 km h -1 ) activity across playing positions in the Europe League according to team ball possession: in possession; not in ball possession. * Significantly longer total distance covered in sprinting when their team was in ball possession and not in ball possession (p < 0.05). 3.2 Technical performance The players had 48.2 ± 12.9 individual possessions per match, with differences among playing positions (p < 0.05) (see Table 2). There were a substantially greater total number 512

10 of ball possessions by central midfielders, external defenders and external midfielders than central defenders. In turn, the central midfielders featured a greater total number of ball possessions than the forwards (p < 0.05) (Table 2). The number of ball touches per individual possession considering all players was 2.0 ± 0.4 and varied between playing positions (p < 0.05). The number of ball touches per possession was similar for the forwards, external midfielders and central midfielders, but differed for external defenders (p < 0.05). Furthermore, the forwards recorded significantly more ball touches than the central defenders (p < 0.05) (Table 2). The examined players spent 54.1 ± 21.4 s per match in possession. There were differences among playing positions (p < 0.05), with external midfielders and central midfielders spending more time in possession than central defenders (p < 0.05) (Table 2). The percentage of successful passes ranged from 69.7% to 76.7% (Table 2) with no difference between playing positions. The highest mean number of successful passes (in percent) was noted in central defenders, and the lowest in forwards. These differences were, however, statistically, non-significant. 513

11 Table 2. Technical characteristics of professional soccer players in the Europe League (mean ± SD). ED (n = 35) CD (n = 39) CM (n = 35) EM (n = 20) F (n = 18) Follow-up Tests (Bonferroni) Total number of ball possessions 55.1 (14.0) 33.4 (12.8) 58.5 (13.1) 53.3 (14.1) 42.3 (10.5) (CM = ED = EM) > CD, CM > F* Number of ball touches per individual ball possession 1.7 (0.3) 1.8 (0.3) 2.0 (0.3) 2.1 (0.5) 2.3 (0.6) (F = EM = CM) > ED, F > CD* Total duration of ball possession [s] 50.4 (29.0) 36.4 (25.3) 62.1 (24.8) 64.9 (30.8) 56.7 (27.0) (EM = CM) > CD* Percentage of successful passes 72.0 (12.3) 76.7 (13.0) 71.3 (13.1) 72.7 (10.3) 69.7 (9.5) (CD = EM = ED = CM = F) ns * Significant difference between playing positions (p < 0.05) 514

12 4. Discussion The required versatile training of modern soccer players must include optimal physical and volitional preparation as well as various technical skills and abilities. Soccer demands from players specific predispositions with regard to their respective positions on the team. The analysis of matches of professional soccer teams reveals that the same training means and methods must not be applied equally to all players regardless of their playing position. The training methodology should be adjusted to particular positions on the pitch and their requirements. Only then can the players fulfill their team duties perfectly (Di Salvo et al., 2007). This adjustment concerns players motor abilities (Krustrup et al., 2005), length of covered running distances (Bradley et al., 2010), especially with high-speed and sprinting intensities (Mohr et al., 2003) and technical-tactical skills (Kannekas et al., 2009; Dellal et al., 2010). The results of the analysis of Europa League matches indicate that the mean total distance covered by elite players regardless of their playing position amounted to 11,168 ± 679 m, which was close to results by other authors (Carling et al., 2008; Di Salvo et al., 2009; Dellal et al., 2010; Carling and Dupont, 2011; Dellal et al., 2011; Andrzejewski et al., 2012). These results point to the significance of aerobic processes which - in professional players - should be studied continuously and thoroughly (Helgerud et al., 2001; Stølen et al., 2005). The role of these processes explains the wide research into determination of the anaerobic threshold (Kemi et al., 2003; Andrzejewski et al., 2012) or maximum oxygen uptake (Sotiropoulos et al., 2009). The analysis revealed differences in the length of total covered distance between players in different positions on the pitch. The longest distance during a game was covered by the central midfielders ahead of external defenders, forwards and central defenders (p < 0.05). The results of the present analysis are confirmed by Di Salvo et al. (2007), who in their analysis of motor activities of 300 soccer players participating in 20 matches of the Spanish Primera Division also indicated central midfielders as players who covered the longest running distances. Also the midfielders (central and external) of the French La Liga in the season ran the longest distances (Dellal et al., 2011) in comparison with other playing positions. It should be mentioned that these authors also used the Amisco Pro computerized system in their match analyses. An interesting research aspect is the economy of motor activities of soccer players in different positions on the pitch. It is measured by the distance covered in offensive play as well as in defensive play. Players movement on the pitch is affected by their technicaltactical preparation, motor predispositions and tasks assigned to particular players by the coach. The analysis of total distance covered by soccer players in the present study showed that the forwards and external midfielders ran longer distances while in ball possession (p < 0.05) than the central and external defenders (Tab. 1). This is confirmed by Dellal et al. 515

13 (2010), who also came to the same conclusions. The longest total distance covered by players in defensive play was covered by the central midfielders followed by external defenders and external midfielders. These results seem to be related to the fact that players in these positions move mostly in the middle part of the field, in which the highest number of passes take place. The midfield is also where the game is played for more than one half of a match. Moreover, the midfielders are the first to attempt to regain ball possession after their team has lost it. Very often they act in the situation of improper defensive formation of their team, which requires even more intensive motor activities from them. The shortest distance in defensive play was covered by the forwards. This can be explained by the fact that these players do not take part or are limitedly involved in the team s defensive actions. One of the criteria used to determine players sports level is the length of distance covered with a high-speed intensity during a match (Di Salvo et al., 2009). The results of the present study show that the high-speed running distance covered by professional Europa League soccer players range between 214 m and 384 m, i.e. 2.1% to 3.2% of the total covered distance (Tab. 1). Similar results were obtained by Dellal et al. (2010) who studied motor activities of players taking part in the French First League, in the season, and in La Liga and the Premier League in the seasons (Dellal et al., 2011). Also Rey et al. (2010) in their match analysis of the Spanish Soccer League in the season noted a similar mean high-speed intensity running distance to the one studied in the current study. The present analysis also revealed differences between high-speed running distances between players in different positions on the team. The shortest distance was covered by the central defenders (p < 0.05), which had been confirmed by a study of Premier League players in the season (Bradley et al., 2009). The specifics of the high-speed running distance with regard to offensive and defensive play were described by Di Salvo et al. (2009). They observed that the central defenders covered the shortest high-speed running distance while in ball possession, i.e. nine-fold shorter than the distance covered by the forwards (Fig. 1). This can be explained by the implementation of tactical tasks assigned to the forwards and their more dynamic play while in ball possession. In defensive play, the longest high-speed running distance was covered by the external defenders, i.e. two-fold longer than the forwards (p < 0.05), as confirmed by Dellal et al. (2010, 2011). This is a consequence of the practice of zone defense in modern soccer, which involves external defenders continuous dynamics. Also the lengths of sprinting distances ( 24 km h -1 ) covered by the studied players varied according to playing position. The longest sprinting distances were covered by the forwards, external midfielders and external defenders. They were significantly longer than the distances by central defenders and central midfielders (p < 0.05) (Tab. 1). The results of the present study correspond to those obtained by Dellal et al. (2011) in their analysis of motor activities of soccer players from the English Premier League and Spanish Premier Division in the season. In the European Champions League ( seasons) the longest sprinting distances were covered by external midfielders, however, they were not significantly longer than those run by the forwards and external defenders. Like in the present study of Europa League players and in Di Salvo et al. (2010), the results 516

14 obtained by players in those three positions differed from those of central defenders and central midfielders. The analysis of the total sprinting distances run by players in offensive or in defensive play revealed considerable differences in their length depending on playing position. In offensive play the central defenders ran decidedly the shortest sprinting distances out of all players on the pitch; however, in defensive play they dominated this particular distance parameter (Fig. 2). These results again can be explained by the nature of technical-tactical tasks assigned to central defenders who are in charge of securing the direct approaches to their goal. Moreover, these players assist the midfielders and forwards and also engage in duels with the forwards of the opposing team. In offensive play (with the exception of set pieces), central defenders are usually not involved in offensive actions and remain at halfway line. The forwards are assigned markedly different technical-tactical tasks on the pitch. These players were shown to cover the shortest sprinting distance while not in ball possession. This is because the forwards are assigned defensive tasks to a very limited extent. The forwards are potentially the first players to attempt regaining ball possession, but it is the players in other positions who take over defensive tasks more swiftly. On the other hand the forwards dominate the sprinting distances while their team is in ball possession. They are extremely engaged in the team s offensive actions such as receiving orthogonal and diagonal passes from their teammates, reaching the opponent s penalty area and, possibly, taking a shot at goal. In offensive play along the sidelines the forwards task is to enter the opposing team s penalty area and attempt to gain control in midair over centered balls. Both the length of sprinting distances as well as their percentage contribution to the total distance covered by players revealed identical relationships between players in different positions on the pitch. The longest relative sprinting distance was run by the forwards (3.1%), i.e. two-fold greater sprinting work rate than central midfielders and central defenders. Similar results were obtained by Dellal et al. (2010, 2011), who also showed that forwards covered proportionally the longest sprinting distances of all soccer players. The present analysis revealed that the Europa League soccer players covered the combined high-speed and sprinting distance between 399 m and 697 m, i.e. between 3.9% and 6.1% of the total covered distance during a match. The mean combined distance at such intensities was about 10% of the total distance (Carling et al., 2008), although in some earlier studies it had ranged between 1% and 12% (Van Gool et al., 1988; Rienzi et al., 2000).These differences are undoubtedly due to different methodologies and interpretations of results. The assessment of playing effectiveness requires the determination of multiple factors affecting players activities during a match. The combination of these factors and construction of indices and models of gameplay make the evaluation of players activity profiles possible. These factors determine the technical-tactical levels of individual players and the entire team. They include the total duration and number of individual ball 517

15 possessions, number of ball touches per individual possession and percentage of successful passes. The analysis of technical activities showed that total duration of ball possession ranged between 36.4 s and 64.9 s, while the total number of ball possessions never exceeded 58.5 possessions, in all ten studied Europa League matches. This data clearly confirm the significant role of players activity in defensive play. As far as the playing position is concerned, the central defenders featured the shortest total duration of ball possession and the lowest total number of ball possessions in comparison with other playing positions (Tab. 2). This can be explained by the central defenders not taking the risk of losing ball possession, simultaneous acceleration of gameplay and moving into the opponent s area. The number of ball touches per individual possession ranged between 1.7 and 2.3, which indicates that technical actions undertaken by professional Europa League soccer players must be executed very swiftly. This swiftness of task execution is an indicator of differences in levels of technical-tactical skills of players at various stages of their soccer training: youth, amateur and professional. The results of the present study show that offensive formation players (forwards, external and central midfielders) recorded the highest number of ball touches in comparison with defensive formation players. These results confirm that offensive players must possess a high level of technical skills allowing them to engage in constant duels with the defenders and creating enough room to execute shots on goal. Similar conclusions had been also reached by other authors (Carling, 2010; Dellal et al., 2010; Dellal et al., 2011). The basic means of soccer play include ball passes that constitute about one half of all activities of players in ball possession (Dufour, 1993). In the present study the highest percentage of successful passes was displayed by the central defenders (76.7%). As for the external midfielders, external defenders and central midfielders, the percentage of successful passes was lower but also exceeded 70%, i.e. 72.7%, 72.0% and 71.3%, respectively. The lowest percentage of successful passes was recorded by the forwards 69.7% (Tab. 2). Players of the Spanish Primera Division and English Premier League were shown to have a similar percentage of successful passes, i.e. from 70 to 81% (Dellal et al., 2011). On the other hand, the French elite players of Ligue 1, revealed differences in percentage of successful passes, with regard to the playing position. The French central defenders reached 63% of successful passes, i.e. lower than their counterparts in the present study. The players in other positions on the pitch attained the percentage above 70%, e.g. 71% in forwards (close to Europa League forwards). The present study confirmed the existence of differences in the effectiveness of physical and technical-tactical activities of players in different positions on the pitch. The study results show that requirements of players fulfilling different roles on the team vary significantly. Modern association football requires from players specific motor and technical-tactical predispositions to play in particular positions on the pitch. The precise determination of these predispositions will enable the development of the type and intensity of training adjusted to particular positions on the team. Defining the possibilities, 518

16 predispositions and skills soccer players should possess will permit the development of activity profiles for each playing position. 5. Conclusions The results of the present study show that despite the significant universalism of activities of soccer players taking part in Europa League matches, the division into offensively predisposed and defensively predisposed players is still valid. The specific and individual players predispositions should be appropriately utilized in the training process accounting for particular tactical formations and playing positions. The observations of behaviors of professional soccer players taking part in Europa League matches point to the fact that players capable of performing multiple efforts of high and very high intensity with and without the ball are in high demand in modern association football. Such players must display high levels of aerobic capacity, lactate tolerance and anaerobic fitness. If during a game their ability to perform sprinting efforts is reduced, it may negatively affect the implementation of technical tasks on the pitch and, in consequence, the team may lose points. The players may show greater fatigue, which could affect their technical actions, ability to play quickly and perception capability. In the training plans, soccer coaches and training managers must account for performance of efforts of high and very high intensities, which constitute from 3.9% do 6.1% of the total covered distance during the game. The Repeated Sprint Ability (RSA) in soccer players should range from 200 m to 500 m, considering the player s position on the pitch. The training of external midfielders, forwards and external defenders taking part in Europa League matches must involve more work of high and very high intensity. The distance covered by these players and the number of actions performed with high intensity are higher than central defenders and central midfielders. That is why the process of selection of players for these team positions must account for their predispositions conditioning their effective performance. It is rather difficult to point out a single and most appropriate training method that can be used for development of Repeated Sprint Ability. Two useful methods can be distinguished. One is based on a traditional model of development of speed abilities and involves multiple, repeated sprints (15-20 m) with rest breaks. This method, in comparison with interval training methods, improves the best sprint time and mean sprint time and thus increases the RSA index. The other method involves modified interval training with a single load of shorter duration than in regular interval training. Each performed exercise is followed by an incomplete rest break. In practice this means that the training players begin the next repetition with incremental fatigue. Unlike speed training, interval training improves the fatigue index and, in effect, reduces the time of a single sprint and a mean sprint time. A better fatigue index 519

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20 Football VI. (edited by T. Reilly and F. Korkusuz), Routledge. pp London: 7. Acknowledgments The authors wish to express their thanks to the authorities of KKS Lech Poznan football club for making their statistical match data available for research purposes. The results of the present study do not constitute endorsement of Amisco Pro or KKS Lech Poznan football club by the authors. Correspondence Marcin Andrzejewski Faculty of Methodology and Recreation University School of Physical Education, Poznan,ul. Królowej Jadwigi 27/ Poznan, Poland Tel: