Soccer as it is played today is a physical activity that

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1 PHYSICAL FITNESS OF ELITE BELGIAN SOCCER PLAYERS BY PLAYER POSITION JAN BOONE, 1,2 ROEL VAEYENS, 2 ADELHEID STEYAERT, 1 LUC VANDEN BOSSCHE, 1 AND JAN BOURGOIS 1,2 1 Center of Sports Medicine, Ghent University Hospital, Ghent, Belgium; and 2 Department of Movement and Sports Sciences, Ghent University, Ghent, Belgium ABSTRACT Boone, J, Vaeyens, R, Steyaert, A, Vanden Bossche, L, and Bourgois, J. Physical fitness of elite Belgian soccer players by player position. J Strength Cond Res 26(8): , 2012 The purpose of this study was to gain an insight into physical and physiological profile of elite Belgian soccer players with specific regard to player s position on field. The sample consisted of 289 adult players from 6 different first division teams. The players were divided into 5 subgroups (goalkeepers, center backs, full backs, midfielders, and strikers) according to ir self-reported best position on field. The subjects performed anaerobic (10-m sprint, m shuttle run [SR], squat jump [SJ], and countermovement jump [CMJ]) and aerobic (incremental running protocol) laboratory tests. The strikers had significantly shorter sprinting times (5-, 5- to 10-m time, and SR) compared with midfielders, center backs, and goalkeepers, whereas full backs were also significantly faster compared with goalkeepers and center backs. The goalkeepers and center backs displayed higher jumping heights (total mean SJ = cm and CMJ = cm) compared with or 3 positions, whereas strikers also jumped higher than full backs and midfielders did. Regarding aerobic performance, both full backs and midfielders ( and mlmin 21 kg 21, respectively) had a higher _ VO2 max compared with strikers, center backs, and goalkeepers ( , , and mlmin 21 kg 21, respectively). From this study, it could be concluded that players in different positions have different physiological characteristics. The results of this study might provide useful insights for individualized conditional training programs for soccer players. Aside from predominant technical and tactical skills, a physical profile that is well adjusted to position on field might enhance game performance. KEY WORDS aerobic performance, anaerobic performance, physiological profile, anthropometry Address correspondence to Jan Boone, Jan.boone@ugent.be. 26(8)/ Ó 2012 National Strength and Conditioning Association INTRODUCTION Soccer as it is played today is a physical activity that requires a high level of conditioning in addition to proficient technical and tactical skills. The game can be characterized as a predominant aerobic exercise combined with frequent intermittent short intense actions with a high rate of anaerobic energy turnover. Reports of match analyses revealed that elite soccer players generally cover 9,500 12,000 m during a 90-minute game (4,8,14,18,24). Approximately 40% of this distance consists of high-intensity running (.14.0 kmh 21 ) with or without ball (18) and 1 11% of sprinting (.19 kmh 21 ) (14). These sprinting exercises of short duration lead to a high rate of creatine phosphate breakdown, which is resynsized afterward during following lower intensity periods (3). The speed of this recovery depends on power of aerobic metabolism ( VO _ 2 max) (20,21). The average work intensity of a soccer game is close to anaerobic threshold (i.e., highest exercise intensity at which removal of lactate equals its production) at a heart rate (HR) of approximately 85% HRpeak (3,12). Based on linear relationship between HR and oxygen uptake obtained during an incremental treadmill exercise test, this HR corresponds to an average oxygen uptake of 75% VO _ 2 max (23). Despite soccer game being dependent predominantly on aerobic metabolism, it should be argued that most decisive actions are covered by means of anaerobic metabolism (i.e., sprinting, jumping, etc.). The intermittent character of a soccer game results in a subsequence of highintensity activities with an accumulation of lactate and periods of low intensity during which removal of lactate can take place. During a soccer game, blood lactate concentration generally varies between 2 and 10 mmoll 21 (1,8,13). This indicates that overall intensity of game is rar high stimulating energy turnover through anaerobic glycolysis and also that measured lactate concentration depends highly on actions preceding blood sampling. These game characteristics (and technical and tactical requirements) impose that physical performance of elite soccer players is based on combination of endurance, speed, agility, and strength. Soccer players refore are bound to have both a high power and capacity of aerobic and anaerobic metabolism VOLUME 26 NUMBER 8 AUGUST

2 Physical Profile of Elite Belgian Soccer Players to be able to perform at highest level. The combined importance of se physical determinants is specific to soccer, and in this way, soccer training needs to be well balanced and structured to optimize player performance without inducing overreaching and overtraining. It should be noted, however, that physiologic and metabolic demands of a soccer game have to be seen in view of player s position. It has been reported that midfielders cover 5 15% more total distance compared with fullbacks, forwards, and center backs and even 20 40% more distance at high intensity compared with forwards and center backs. Forwards and full backs spent 20 40% more time sprinting compared with midfielders and center backs (4,6,7,14,17). The results of se studies show that different positions on field are characterized by specific physical activities and demands. Next to motion analysis to obtain information on physiological demands of a soccer game, laboratory and field measurements might be useful to evaluate physiological characteristics of players in reflection to specific demands of different positions on field. The aim of this study was to test wher a laboratory test battery could distinguish se specific characteristics between players from various positions on field. In this way, this study could contribute to identify physical profile (i.e., strengths and weaknesses) of players conform ir position on field and facilitate individualization of training. It should be noted that physical profile, next to technical and tactical skills, is an important determinant for level of a player. Several motion analysis studies have shown that level of player influences activity pattern on field. High-level players not only cover a higher total distance but y also perform a higher amount of high-intensity activities (12,14) during a soccer game compared with players of a lower level. Therefore, individualization of training, based on position on field and individual weaknesses, is important for enhancing performance during a soccer game. In line with content of this study Sporis et al. (22) determined fitness profile of elite Croatian soccer players. It was observed that anthropometric features and aerobic and anaerobic performance differed among different playing positions. In this study, physical profile of Belgian elite soccer players incorporating anthropometric characteristics and aerobic and anaerobic performance was examined. Furrmore, we wanted to acquire an insight into wher physical profile of players varied according to different positions on field. Based on abovementioned motion analysis studies (e.g., [4,6]), we hyposized that aerobic characteristics would be more dominant in midfielders and fullbacks compared with forwards, whereas forwards and defenders would display a higher anaerobic power and capacity inherent to specific characteristics and demands of different positions on field. METHODS Experimental Approach to Problem To allow extrapolation of results in this study (i.e., physical and physiological profile) into training practice of elite soccer players and teams throughout world, one of main conditions is that a representative group of players is used. Therefore, a large (n = 289) subject group was tested consisting of elite soccer players in Belgian first division (championship level). Among this test group, 41 players had also been selected to play in National Team of ir country. Respectively, 11 and 9 players were active in World Championship of 2006 in Germany and 2010 in South Africa. To obtain an insight into physical and physiological profile, subjects completed a battery of both laboratory-based anaerobic and aerobic tests. The anaerobic tests incorporated both sprint and jump tests in line with anaerobic movements inherent to soccer game. To examine reactivity and speed, a 10-m sprint was performed, whereas agility was tested by means of a m shuttle run (SR). The jump test consisted of a squat jump (SJ) and a countermovement jump (CMJ) to obtain information on specific jump strength (explosive power). In addition to anaerobic tests, subject performed an incremental running test to examine aerobic performance and running speed at anaerobic threshold. A large subject group was used to obtain a sufficient number of players for each position on field so that a reliable representation of physical and physiological profile of elite Belgian soccer player could be made. Subjects The test group consisted of 289 professional soccer players (age: years) active in Belgian first division between 2003 and The subjects played in 1 of 6 teams, which attended Laboratory of Exercise Physiology of Centre of Sports Medicine of Ghent University Hospital (Ghent, Belgium) for physical tests in preseason phase. Three of 6 teams finished in 8 seasons between 2003 and 2010 at least 6 times among 5 best teams in first division and were, refore, also active in Champions League or Europa League/Union of European Football Associations (UEFA) Cup. The subjects were divided into 5 groups according to ir self-reported best position on field: center backs (n = 60), full backs (n =82),midfielders(n =68),strikers(n =62),and goalkeepers (n = 17). This study had approval of Ethical Committee of Ghent University Hospital, Ghent, Belgium. All participants were fully informed about nature and demands of study, and known health risks. They completed a health history questionnaire, signed an informed consent document, and were informed that y could withdraw from study at any time. Experimental Protocol The physical tests were performed 2 4 weeks before start of season. In this period, club training consisted mainly 2052

3 of specific soccer training sessions with occasionally a basic running training. The subjects were asked to abstain from strenuous exercise 24 hours before tests. The tests were performed between 8.30 AM and 5 PM. The experimental protocol consisted of 4 parts: anthropometric measurements, sprint tests, jump tests, and an incremental running test on a treadmill. It took approximately 90 minutes for 1 subject to complete entire test battery. Throughout tests, subjects were clearly instructed about procedures, and y were verbally encouraged to give ir maximal effort. During whole testing battery, laboratory was air conditioned at a temperature of 21 C. It took approximately 90 minutes for subjects to complete entire testing battery. The subjects were wearing a standard soccer kit. Anthropometry. Before physical tests, body height (60.1 cm), body weight (60.1 kg) (Seca balance), and body fat percentage of subjects were determined. The fat percentage was calculated by means of measurements of skinfold thickness using a Harpenden skinfold caliper. The skinfolds were measured at 10 locations (15). Two experienced test leaders assessed anthropometric measurements throughout entire study. Sprint Exercise. The sprint exercise consisted of 2 different exercises. First, subjects had to sprint for 10 m with time recorded electronically by light sensors at both 5 and 10 m (Ergo Tester, Globus, Italy). An auditory cue was used as a starting signal for subjects. This exercise was performed twice, and best result was retained for data analysis. In second test, subjects performed an SR in which subjects had to run 5 times 10 m as fast as possible. The same auditory cue was used for 10-m sprint. The subjects had to cross 10-m marks with 1 foot while turning. The first test was used both to obtain information about both reaction time and starting speed (explosiveness) of players, whereas second test was used to evaluate ir agility in combination with speed. Jump Exercise. After sprint tests, subjects performed SJ and CMJ. They performed both jumps without arm movement (i.e., with hands in hips). For SJ, subjects took a deep position with a knee angle of 90. The flexion of hips could be chosen freely. The subjects remained in this position for 3 seconds. In CMJ, subjects were instructed to jump as high as possible without furr guidelines concerning knee and hip angles. Each jump test was performed twice. The best result was recorded for data analysis. The jumping height was calculated from flight height from jumping mat measured with Ergo Tester (Globus). Incremental Running Test. The incremental exercise consisted of steps of 3 minutes starting from a speed of 8 kmh 21,and speed was increased with 2 kmh 21 after each step. During test, slope of treadmill was set at 1.5% (11). At end of each step, a blood sample was taken from fingertip to determine concentration of lactate in blood by means of a lactate analyzer (1500 Sport, YSI, Yellow Springs, OH, USA). When blood lactate concentration had passed threshold of 4 mmoll 21, subjectshadtoperformafinalsteptoexhaustionin which speed was increased by 1 kmh 21, but slope of treadmill was increased 0.5% each 30 seconds until volitional fatigue. The subjects were encouraged verbally to obtain individual s maximal effort. During test, oxygen uptake was registered by means of a metabolic measurement system (Jaeger Oxycon Pro, Hochenhausen, Germany). The Jaeger Oxycon Pro and Lactate analyzer were calibrated before each exercise test. Statistical Analyses Sprint Exercise. The time at 5 m was used as a parameter of reaction time and explosiveness, whereas difference between time at 5 and 10 m was considered as a measure of speed. The time for SR was used as a measure for speed and agility. Jump Exercise. The jumping heights for squat and CMJs were used as a measure of anaerobic power. Incremental Running Test. The peak performance was determined as maximal speed (Vmax) and slope (Smax) that could be maintained for full 30 seconds in final step. The maximal oxygen uptake ( VO _ 2 max) was determined as highest 30-second average of breath-by-breath values obtained from metabolic measurement system. The anaerobic threshold was determined at a lactate concentration of 4 mmoll 21 (9) and was expressed as a speed in kilometers per hour (V AnT ). The Statistical Package for Social Sciences SPSS 15.0 (SPSS Inc., Chicago, IL, USA) was used for statistical analysis. For 5 positions, descriptive statistics (mean values 6 SD) were calculated for height, weight, fat percentage, VO2 _ max, V AnT, and 5m- and 10-m times, SR, SJ, and CMJ. These parameters were compared between 5 positions by means of a Repeated Measures analysis of variance (5 3 1). If analysis of variance (ANOVA) was significant, Tukey post hoc tests were performed. The reliability of anaerobic sprint and jump tests was determined by means of test-retest method. The reliability analysis (Cronbach alpha) and intraclass correlation coefficients showed that se anaerobic tests were highly reliable. The reliability coefficients (alpha) were respectively 0.91, 0.92, 0.88, 0.90, 0.89 for 5-m times, 10-m times, SR, SJ, and CMJ, respectively. Also, ICCs for 5-m times (0.88), 10-m times (0.90), SR (0.81), SJ (0.87), and CMJ (0.84) confirm reliability of tests. Before setting significance level, a power analysis was performed. This analysis revealed a statistical power of 0.94, and refore, a significance level of p, 0.05 could be used. VOLUME 26 NUMBER 8 AUGUST

4 Physical Profile of Elite Belgian Soccer Players TABLE 1. Mean 6 SD height, weight, and body fat 6 SD for 5 different positions on field. Goalkeepers Center backs Full backs Midfielders Strikers Height (cm) * * * Weight (kg) * * Body fat (%) * The labels, *,,, are used to show significant differences between 5 positions. The same label indicates that parameter did not differ between positions. Positions with a different label differ significantly. p, 0.05 was used as level of significance. RESULTS Anthropometry The overall mean height and weight of subjects were cm and kg, respectively, with a mean body fat percentage of % (Table 1). The ANOVA revealed that goalkeepers and center backs were taller and heavier compared with full backs and midfielders (p, 0.05). The height of strikers did not differ significantly from goalkeepers (p =0.67)and defenders (p = 0.54), but on average, former had alowerweight(p, 0.05). The body fat percentage was significantly higher in goalkeepers compared with 4 or positions (p, 0.05). Anaerobic Performance The parameters of anaerobic performance are presented in Table 2. The mean time for 5 m, as a measure of reaction time and explosiveness, in total subject group was seconds. The 5-m time was significantly lower in strikers compared with goalkeepers (p = 0.03), defenders (p, 0.01), and midfielders (p = 0.04). Also, full backs had a faster time compared with that of defenders. The mean time between 5- and 10-m mark was seconds. The strikers displayed a significantly lower time compared with that of goalkeepers (p, 0.001), defenders (p, 0.01), and midfielders (p = 0.03). For SR ( m), overall mean time was seconds. The strikers were significantly faster than goalkeepers (p, 0.01), defenders (p, 0.01), and full backs (p = 0.02), whereas midfielders were faster than goalkeepers (p = 0.02) and center backs (p, 0.001). The mean jump heights for SJ and CMJ were and cm, respectively. The statistical analysis revealed that goalkeepers and center backs had a higher jumping height compared with full backs (p, 0.001) and midfielders (p, 0.01). Also forwards had a higher CMJ height compared with full backs (p =0.03) and midfielders (p = 0.03). Aerobic Performance The parameters of aerobic performance are presented in Table 3. The mean peak performance for incremental exercise test was 15.6 kmh 21 with a slope of 4.4%. The mean _VO 2 max for total subject group was mlmin 21 kg 21, and mean running speed at level of anaerobic threshold (4 mmoll 21 ) was kmh 21. The full backs and midfielders had a higher _ VO 2 max and V AnT compared with strikers (p =0.03andp = 0.02, respectively) and center backs (p, 0.01), which in turn had ahigher _ VO 2 max and V AnT than goalkeepers (p = 0.03). The maximal blood lactate value at end of incremental running test was on average mmoll 21,andthis value did not differ between 5 positions (p. 0.05). TABLE 2. Mean 6 SD 5-m time, 10- to 5-m time, SR, SJ, and CMJ 6 SD for 5 different positions on field.* Goalkeepers Center backs Full backs Midfielders Strikers 5 m (s) m (s) SR (s) k k SJ (cm) * CMJ (cm) *SR = shuttle run; SJ = squat jump; CMJ = countermovement jump. The labels,,,,k, are used to show significant differences between 5 positions. The same label indicates that parameter did not differ between positions. Positions with a different label differ significantly. p, 0.05 was used as level of significance. 2054

5 TABLE 3. Mean 6 SD _ VO 2 max, speed at anaerobic threshold (V AnT ), and lactate concentration at end of incremental running test 6 SD for 5 different positions on field. Goalkeepers Center backs Full backs Midfielders Strikers _VO 2 max (mlmin 21 kg 21 ) * V AnT (kmh 21 ) * [Lactate] (mmoll 21 ) * * * * * The labels, *,,, were used to point significant differences between 5 positions. The same label indicates that parameter did not differ between positions. Positions with a different label differ significantly. p, 0.05 was used as level of significance. DISCUSSION The purpose of this study was to gain an insight into general fitness level of elite soccer players active in Belgian first division. A large subject population was tested for anthropometric characteristics and for anaerobic and anaerobic performance. Furrmore, we wanted to test wher se different aspects of general fitness level would vary according to position of player of field. As hyposized, results of this study clearly show that anthropometric, physical and physiological characteristics differ according to specific demands inherent to position on field. The _ VO 2 max that is reported in literature varies in general between 55 and 65 mlmin 21 kg 21 for elite soccer players (8,10,16,22). The mean _ VO 2 max of elite soccer players in this study ( mlmin 21 kg 21 ) was in line with se studies. The differences between studies can be attributed to experimental protocol (i.e., protocol of incremental exercise, metabolic measurement system, etc.), testing period with respect to phase in season or level of players. In this context, it should be noted that Belgian competition is not among strongest in Europe. However, considering performances in Champions League and Champions League and Europa League (formerly known as UEFA Cup), level of Belgian competition (ranked 14th in UEFA country ranking) is very comparable (or even stronger compared) to Croatia (22nd) (22), Norway (27th) (10), and Sweden (24th) (8). Compared with aforementioned studies, performance in squat and CMJ was slightly lower (on average 3 cm) in this study. It should be noted, however, that mean age of subject group in this study was lower ( years) in comparison with most or studies in which mean age is approximately 28 years. This might explain lower anaerobic performance (SJ and CMJ) compared with or studies. Soccer players are generally at ir peak performance at age of years, and refore, subjects in our test group have a few more years to develop ir explosiveness and strength. The position of goalkeeper on soccer pitch requires relatively low demands from aerobic energy metabolism. The goalkeeper generally covers about 4 km during a soccer game (19), and most of his actions are determined predominantly by anaerobic power, that is, jumping and sprinting. In this study, goalkeepers had a significantly lower VO _ 2 max and performance at anaerobic threshold compared with or positions. On or hand, y exert a high anaerobic power, especially during jumping test. In combination with ir body size, goalkeepers are on average tallest players in team, and y have a high reach and y can cover a large part of goal, which is necessary to efficiently avoid opponent to score. In this study, goalkeepers also had a higher body fat percentage compared with that of or positions. This can probably be attributed to lower amount of aerobic training. The average sprinting performance might also be in part related to higher body fat percentage. Also, proportional contribution of strength and sprint training in training regime of goalkeeper, with an important role for strength training with an increase in muscle mass as a consequence, might attribute to average speed and agility. With regard to field players, center backs generally cover shortest distance (14,17). The center backs need strong positional play with a good headplay. They perform a smaller number of explosive sprint movements during soccer games. Generally, y play only a minor role in support of attack, and y only move to front for corner kicks or free kicks. According to present data, ir physiological profile is in line with se specific positional demands. Apart from goalkeeper, y not only have lowest VO2 _ max and running speed at anaerobic threshold, but ir anaerobic sprint performance and agility are also rar low. This is in line with findings of or studies with elite soccer players (2,22). The lower sprint and agility performance is probably because of large body size, which hinders sudden changes in direction during SR and in extension on pitch. Their anaerobic power for jumping is higher compared with or positions, and in combination with ir body size, this benefits ir headplay, which is an important part of defensive skills. The midfielders and full backs generally cover largest distance during a soccer game, on average km VOLUME 26 NUMBER 8 AUGUST

6 Physical Profile of Elite Belgian Soccer Players (3,4,8). These players have both defensive and offensive tasks including frequent movements up and down field. Therefore, this requires a well-developed aerobic capacity. Similar to or studies (2,22), this study revealed that se players had highest aerobic power and performance at anaerobic threshold compared with or positions. In this study, it was observed that full backs had a slightly higher sprinting ability (i.e., 5 and 10 m) but appeared to have a lower agility compared with that of midfielders. Although full backs predominantly need explosiveness and speed to pass an opponent along line, midfielders need to be able to change directions more appropriately and to accelerate with changes in direction. The specific characteristics in response to se specific demands of full back and midfielder position appear to be present in physical profile of players, although differences were not significant. In addition, jumping performance was slightly higher in midfielders, which more frequently need to use ir headplay compared with full back. The strikers have higher aerobic capacities ( _ VO 2 max and V AnT ) compared with goalkeepers and defenders but lower compared with full backs and midfielders. This is in line with covered distance during a soccer game ( km), which is higher than that of defenders but lower than that of midfielders. Attackers will cover a large amount of total distance using short sprints, and y need a high explosiveness and speed to be able to pass defenders. In this study, strikers had fastest sprinting times and best agility. In contrast to study of Sporis et al. (22), defenders in our study were significantly slower compared with strikers. This can probably be attributed to classification of position of field. In our study, full backs were separated from central defenders. Because full backs are faster than central defenders, this might have influenced results in study of Sporis et al. (22). The strikers also had a higher jumping performance compared with that of midfielders and full backs but lower compared with defenders. Strikers need a strong jumping ability to be able to control long pass from defenders or to head ball through or back to one of his teammates. Therefore, strikers need a high anaerobic sprint performance and also need a relatively high aerobic performance in combination with a relatively high anaerobic jumping performance. PRACTICAL APPLICATIONS This study contributes to literature on physical and physiological profile of soccer players, especially in regard to elite level of subjects in combination with large sample size. In a recent study of Sporis et al. (22), a similar research was performed in elite Croatian football players. In this study, however, only 4 different positions were considered, that is, goalkeepers, defenders, midfielders, and forwards. It should be noted, however, that position of a full back is characterized by different physical demands compared with a center back (7). Therefore, in our opinion, position of full back should be considered as a separate position on field beside center backs, especially because it was observed in this study that fitness profile of a full back more closely resembles that of a midfielder. The information of this study, reporting physiological profile of elite soccer players, can be useful for training staff into optimization of training process to maximize performance level specific for role of player in team. Furrmore, in team sports, where re is a tendency for early specialization concerning position on field, se physiological profiles can be used in selection of a player for a position and for development of specific training programs based on important characteristics of position of field. It should be noted that motion analysis of soccer games was not included in our study. This motion analysis provides important information on physical characteristics of a soccer game especially with regard to different positions on field. However, disadvantage of se match data is that se measures are performed in a situation that strongly depends on strength of own team and of opponent, tactical gameplay, and wear conditions (4,5,12,18). The measures performed in this on or hand are conducted in a standard situation following strict guidelines, and refore, se measures provide valuable insights into physical characteristics of players. The combination of both laboratory measures and motion analysis on field could provide important additional information on physical demands of positions on field and on main factors that determine individual performance. From this study, it could be concluded that physical profile of elite soccer players in Belgian competition is specific inherent to specific demands of position on field. It is not clear, however, wher process of obtaining a specific position on field is a matter of natural selection, based not only on physical profile but also on technical-tactical skills, team cohesiveness and even match performance, or wher specific physical profile is a consequence of specific demands of position itself which player has grown into. In modern game of soccer, however, it is clear that adult players need to be trained specifically according to ir position on field to optimize performance of team. The physical profile provided in this study can help coaches in identifying physical characteristics, which are important for different positions to optimize training and performance of each individual player. On or hand, physical profile can also help coaches to direct younger players to position that corresponds best to ir physical profile. ACKNOWLEDGMENTS The results of this study do not constitute endorsement of product by authors or National Strength and 2056

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