JPES. Original Article. The usefulness of small-sided games on soccer training

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1 Journal of Physical Education and Sport (), 12(1), Art 15, pp , 2012 online ISSN: X; p-issn: ; ISSN - L = Original Article The usefulness of sall-sided gaes on soccer training FILIPE CLEMENTE 1, MICAEL S. COUCEIRO 2, FERNANDO M. L. MARTINS 3 4, RUI MENDES RoboCorp, Faculty of Sport Sciences and Physical Education University of Coibra, PORTUGAL 2 RoboCorp, Engineering Institute of Coibra Polytechnic Institute of Coibra, PORTUGAL 3 RoboCorp, Coibra College of Education Polytechnic Institute of Coibra, PORTUGAL 4 Instituto de Telecounicações (Covilhã), PORTUGAL 5 Interdisciplinary Centre for the of Huan Perforance, Lisbon Technical University, PORTUGAL Published online: March 31, 2012 (Accepted for publication March 22, 2012) Abstract The specificity of collective sports training has evolved to adapt according to ecology stiuli inherent to the sport. In this sense, the coaches have adopted exercises based on the gae, designated by sall-sided gaes. In football practice this type of exercises triggers very receptivity on the part of coaches. In this sense, this paper analyzes the relevance of this type of exercise and as ay be appropriate depending on the specific needs of the players. Task constraints as field diensions, nuber of players for exercises or objectives of the task showed effects on physiological and technical variables of the players. Consequently this article will exaine through a literature review, the effects related to the task constraints in order to ephasize the assive relevance of sallsided soccer gaes. Key words: Sall-sided gaes, training, task constraints, soccer. Introduction Physiological, social, psychological, technical and tactical factors can influence the perforance of soccer players (Bagsbo, 1994), i.e., the aggloerations of factors are iportant constraints that influence directly the perforance over tie. Therefore the training conception should consider all these factors in order to develop, integrally, the soccer players (Jones & Drust, 2007). In high perforance sports it has been well accepted that the axiu benefits of exercises are achieved when the training stiuli are siilar to the copetitive deands Bopa, 1983; Mallo & Navarro, 2008). Therefore, physical factors can be carried out in a ore soccer specific way than plain running (Hoff, WislØff, Engen, Kei & Helgerud, 2002). Thus, in order to integrate the reality of the gae on training, the coaches try to eulate the physical, technical and tactical requireents, adapting the task to specificity of the gae, reducing its fors and adapting training objectives MacLaren, Davis, Isokawa, Mellor & Reilly, 1988; Hoff, et al., 2002; Reilly & White, 2004; Mallo & Navarro, 2008). In this way technical and tactical factors are involved and trained in proxial conditions to soccer atch, in order to proote an effective transfer to the copetitive environent and develop at sae tie the tactical principles, taking advantage to the training tie (Willias, Horn & Hodges, 2003). Coonly the literature indicates that these adaptations of the gae, reducing the gae at sall parts, are designated as sallsided gaes. Therefore sall-sided gaes are generally used by coaches in order to develop the technical skills or aerobic fitness of soccer players Rapinini, Ipellizzeri, Castagna, Abt, Chaari, Sassi & Marcora, 2006; Hill-Haas, Coutts, Rowsell, & Dawson, 2008; Hill-Haas, Dawson, Coutts & Rowsell, 2009). The design and introduction of the specific training exercises depends, unavoidably, of factors associated with the tea's context and their objectives. Factors such as conditional capabilities of the players, the season stage, recovery tie in relation to post or pre gae, tea's strategic objectives, technical level of players or the level of collective perforance, are factors that should be considered at the oent of designing the training exercises. In fact, the adequation of exercise specificity to the context can be a key factor predicting the activity success. Therefore the coplexity level of exercise directly depends of the factors conjugacy previously described. Nevertheless at scientific level soe factors can't be attended as a specific strategic of tea or specific season stage and their specific context. However recent studies Hill-Haas, Dawson, Ipellizzeri & Coutts, 2011) suggest the assive relevance of sall-sided gaes application in order to iprove the quality and training specificity. In fact, are not only a technical or physiology factors that can be iproved through sallsided gaes, in fact, available evidence suggests that these constraints (i.e., playing area and nuber of players) proote higher levels of enjoyent and dedication aong players iproving, at sae tie, the level of play (Wall & Côté, 2007; Sapaio, Abrantes & Leite, 2009). Regarding to physiological factors is possible to analyze that the physiological indicators depends of the exercises characteristics (Aroso, Rebelo & Goes-Pereira, 2004). Studies on sall-sided gaes suggest that, Corresponding Author: Filipe Cleente Eail: Filipe.cleente5@gail.co 93

2 heart rate responses are around 90-95% of axial heart rate Hoff, Engen, Kei. & Helgerud, 2002; Kelly & Drust, 2009) and these sae gaes can iprove aerobic fitness and, at sae tie, specifically physical atch perforance (Helgerud, Engen, Wisloff & Hoff, 2001). In fact soe studies had exained the relevance and influence of task constraints field size, player s nuber, task goals or coach encourageents) on intensity of sall-sided gaes Owen, Twist & Ford, 2004; Rapinini, et al., 2006; Jones & Drust, 2007). Soe alterations on physiology variables heart rate, blood lactate or rating perceived exertion) has been reported Little & Willias, 2007; Dellal, et al., 2008). Equally, kineatical analysis distance covered, intensity profile of players) suffered oscillations influenced by task constraints at sall-sided gaes Casaichana & Castellano, 2010). Concerning to technical aspects, the inclusion of atch-specific activities such as passing, shoots or tackling in sall-sided gaes can adequate the training to real deands of sport (Rapinini, et al., 2007). Soe studies, beyond analyzing the physiological factors, consider technical eleents of players on each sall-sided gae Jones & Drust, 2007; Katis & Kellis, 2009; Casaichana & Castellano, 2010). In fact task constrains as field size or nuber of players can influence the frequency of technical eleents of each player. Soe studies noted that field size represents an iportant factor that constrain the nuber of ball contacts or type of passes ade by players Jones & Drust, 2007; Casaichana & Castellano, 2010). In the sae way, the nuber of players on the sall-sided gae influence technical eleents ade by players Katis & Kellis, 2009; Rudolf & Václav, 2009). Therefore the usefulness of the sall-sided gaes is real and, at sae tie, a assive opportunity in order to iprove the quality of the tea play. However, their application need an careful thinking in order to achieve the ain goals of the coach, i.e., sall-sided gaes need to be adapted to the context considering the physical, technical and tactical level of each tea. The sae exercise ay not result in the sae way on two different teas, or even, in different oents of season for the sae tea. Thus, coach need to use ultiple factors or task constraints in order to adapt the sall-sided gaes to training objectives. Therefore, the ain goal of this work was analyze constraints coonly adopted by researchers on soccer training, in order to understand how sall-sided gaes and their constraints influence on players perforance. Effects of Nuber of Players Nuber of players on the field at each sall-sided soccer gaes can influence the intensity and the physiological effects of the gae. Nuber of players by each gae influence the running and they intensity, frequency of ball contacts or kineatical of the players. However in order to analyze just the intensity effects influenced by the nuber of players, the playing area should be kept constant (Rapinini, et al., 2007). However the analyzed studies do not include this perspective (i.e., keeping field size). Nevertheless, the influence of nuber of players needs to be analyzed in order to understand their potentiality to the soccer training. Physiological and Kineatical Effects Jones and Drust (2007) analyzed the influence of nuber of players at sall-sided soccer gaes on heart rate responses. Authors tested and 8 v 8 sub-phases. The results deonstrated that the nuber of players have not changed significantly the heart rate responses. Nevertheless, the anipulation of the nuber of players sees to have a sall ipact on the work-rate profiles observed. However these ipacts don t differ statistically. Additionally, Jones and Drust (2007) study, shows that no significant differences were observed in either the total distance covered or the distance covered by walking and jogging aong gaes. Using ore sub-phases, Little and Willias (2007), found significant differences aong all training drills except for just 3 of the 15 post hoc coparisons (2 v 2 and, 2 v 2 and 8 v 8, and 8 v 8). Generally, authors observed an increased heart rate response to the sall-sided soccer gaes using fewer players, although the 2 v 2 gae showed a significantly lower response than and constituting an exception. Table 1. Studies that analyzed the physiological and kineatical ipacts of nuber of players Distance Covered Jones & Drust (2007) 8 v Structure 10 in 10 in n 8 Heart Rate 175±10 beats/in 168±6 beats/in Total 778± ± 103 Low intensity walking) 181 ± ± 77 Highintensity jogging) 315 ± ± 69 Very highintensity sprinting) 143 ± ±

3 Little & Willias (2007) Rapinini et al. (2007)* *In their study authors are give equal conditions with and without coach s encourageent. Our results just present without coach s encourageent. Dellal, et al. (2008) 2 v 2 8 v 8 1v 1 2 v 2 8 v 8 8 v 8 10 v x x x x x x x x x x x x x x x x x 45 4 x 2 in 4 x 3.30 in 4 x 4 x 6 in 3 x 8 in 4 x 8 in 4 x 1 in, 30 sec 6 x 2 in, 30 sec 2 x 2 x 10 in 4 x 90 x 45 in % HRax 91% HRax 90% HRax 89% HRax 88% HRax 88% HRax 87.6 ± 1.7 HRax 88.6 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

4 Hill-Haas, Dawson, Coutts & Rowsell (2009) Katis & Kellis (2009) Rodríguez-Marroyo, Pernía & Villa (2009) 2 v 2 7 v 7 11 v x x x x x 4 in 10 x 4 in 2 x 30 in 2 x 35 in ± 4 HRax 85 ± 4 HRax 83 ± 4 HRax 87.6 ± 4.77 HRax 82.8 ± 3.22 HRax 79 HRax 76 HRax 2574 ± ± ± ± ± ± ± ± ± ± ± ± 22 At Rapinini et al (2007) study, results suggested that less nuber of players increased the intensity of the gae. Additionally was possible analyzed that the heart rate ean at each gae reduced gradually at sae tie that the nuber of players increased. Contrarily at sae tie that nubers of players decreased the nuber of ball contacts by each player increased. According to these results, Balso (1999) suggested that the less nuber of players ay increase the ball contacts by each player. These ball contacts and the associated activity ay increase directly the intensity of the biological responses of the players. Therefore the results ay confir Reilly and Ball (1984) that suggested that running with the ball requires greater energy expenditure than running without ball contact, explaining the ost intensity on sall-sided gaes with less nuber of players. The sae kinds of results are found by Hill-Haas, Dawson, Coutts and Rowsell (2009). In their study, 2 v 2 sub-phase caused a greater aount of tie spent at 490% Heart Rate ax than the and subphases. These results ay suggest that saller gae forats caused higher ean heart rate responses, with players spending ore tie in the higher heart rate zones (Hill-Haas, Dawson, Coutts & Rowsell, 2009). In the sae line, sall-sided soccer gae displayed higher exercise intensity copared with the gae situations, verified on Katis and Kellis (2009) study. According to Owen, Twist and Ford (2004) adding players to a sall-sided soccer gae in general caused a decrease in ean heart rates and a decrease in ean peak heart rates. Therefore, the results are consistent indicating that sall-sided gaes with less nuber of players ay increase the heart rate and kineatical effects on players. These results suggest that intensity of the exercise ay be anipulated by the coaches, through task constraints in order to proote the developent of physiological paraeters. Copleentally, at the sae tie that coaches influencing physiological and kineatical factors on players, ay iprove the quality of the tactical and technical factors training at specificity of the gae, i.e., considering the soccer ecology. Thus nuber of players can be used in order to iprove the quality of the training and, at sae tie, iprove the fitness of each player, training at specificity. Technical Effects The nuber of players can odify technical requireents of each player. In fact, fewer players can provide an increase of the player s intervention on atch, reducing the variability of the possibilities of passes. Contrarily, the ore nuber of players ay provide another tactical definition to the gae. Therefore, soe studies analyze the influence of nuber of players at sall-sided soccer gaes in order to understand the potentiality of this strategy. Using 8 v 8 and soccer sub-phase, Jones and Drust (2007) found significantly differences on ball contacts. In fact, authors found that the nuber of ball contacts increased on sall-sided gaes with less nuber of players. Therefore authors suggested that tactical requireents placed on the individual players when the nuber of players is altered. For one hand 8 v 8 restricted players to tactical positions and issions defensive, idfield, forward) and, for another hand on players don t have a static ission attacking and defending at every atch-play. 96

5 Table 2. Studies that analyzed the technical ipact of nuber of players Jones & Drust (2007) 8 v 8 Katis & Kellis (2009) Rudolf & Václav 8 v 8 (2009) 11 v x x 60 Structure n Ball Contacts 10 in 36± in 13±7 10 x 4 in 10 x 4 in 34 Short Passes Long Passes 30 in 143 passes in passes in Shots Dribbling Goals ± 48 ± 5 ± 3 ± 9 ± 11 ± 34 ± 11 ± 1 ± 6 ± passes 15 Through Platt, Maxwell, Horn, Willias and Reilly (2001) study was possible analyzed that when young players participated in sall-sided gaes had ore opportunities to perfor skills such as dribbling, passing and shooting than on sall-sided gaes. Siilar results were found by Katis and Kellis (2009) study where authors observe that the nuber of individual eleents increased on sall-sided gaes with less nuber of players. Thus the nuber of players in a tea proved an iportant factor that can affect the frequency of executing offensive gae-related activities by each player (Rudolf & Václav, 2009). Generally, adding players to a sall-sided soccer gae causes an increase at total nuber of technical actions, but generally the total nuber of technical actions per player decreases (Owen, Twist & Ford, 2004). Therefore, suarily, is possible observe that in youth foration phase, the less nuber of players by each sall-sided gaes can give an iportant opportunity to the players increase the frequency of skills perfored. In fact, the progressivity of the nuber of players by each sall-sided gae ust be done according to the learning and specialization phase of the players. Less nuber of players by sall-sided soccer gaes is recoended to practice at lower level of player specialization and, with the increase of the player's quality level, is recoended the increase of nuber of players by each sall-sided soccer gae. Effects of The field size can influence the kineatical indicators presented by soccer players. More or less space to run or to receive the ball and coplete the pass ay be influenced by the field size provided on soccer exercise. Therefore, coach need to conteplate this task constraint in order to iprove the efficiency of the training and the fulfillent of the ain goals. Physiological and Kineatical Effects Coaches can adapt the training intensity through variation of the size of the field (Tessitore, Meeusen, Piacentini, Dearie & Capranica, 2006). Generally, field diensions ay alter the kineatics of oveent relative to each player. Basically, the space for ball progress and carry out their actions are directly related with the space between players as well as with the free space to ake decisions. In this sense, the player ay be constrained by the diensions of the field, triggering changes in physiological and kineatical paraeters. Spaces with lower diensions ay proote ore braking, changes of otion or acceleration. By other side, larger diensions of the field ay allow to the players ore tie to ove, to carry out their actions in a planned and with ore space. Table 3. Studies that analyzed the physiological and kineatical ipacts of field size Rapinini et al. (2007)* 12 x 20 Structure n Heart Rate Total Distance Covered Low intensity walking) Highintensity jogging) Very highintensity sprinting) ±

6 *In their study authors are give equal conditions with and without coach s encourageent. Our results just present without coach s encourageent. Kelly & Drust (2009) Casaichana & Castellano (2010) 15 x x x x x x x x x x x x x 44 4 x 4in 4 x 4in 4 x 4in 8 in 8 HRax 88.6 ± ± ± ± ± ± ± ± ± ± ± 3.6 HRax 175 ± 9 beats in ± 11 beats in ± 6 beats in -1 8 in 8 in ± 5.8 HRean 88.5 ± 4.9 HRean 88.9 ± 3.9 HRean ± ± ± 50.0 Walking ± 27.7 Running ± 41.7 Walking ± 30.4 Running ± 54.0 Walking ± 37.2 Running ± ± ± ± ± ± ± 58.9 Literature don't shows consensus concerning to the real effects of field diensions in the heart rate of the players. On the one hand, results of Rapinini et al (2007) study showed that heart rate was higher during sall-sided gaes played on a large field than on ediu-sized and sall ones. Confiring Rapinini et al (2007), Casaichana and Castellano (2010) indicate that when the individual playing areas were bigger, the 98

7 physical and physiological workloads and the ratings of perceived exertion were all higher. Furtherore, the effective playing tie was also higher when the individual playing areas were bigger. These kinds of results are equally found by Owen, Twist and Ford (2004) showing that enlarging the field diension used for the sall-sided gae by 10 eters generally caused increase at ean heart rates and ean peak heart rates. By the other hand, results of Kelly and Drust (2009) showed a slight increase of ean heart rate on sall-sided soccer gaes with less area. However these results were not significantly. Is iportant to consider that, contrary to the others studies that practice in continuously for, the Kelly and Drust (2009) study, proote the practice on interittent for, i.e., with less tie and ore repetitions. Therefore, results are no conclusive concerning to real effects of field diensions on physiological and kineatical factors. However, is possible to suggest that ost space ay increase the general intensity of the exercise reflecting on an increase of the ean heart rate. Technical Effects The field size can be an iportant task constraint used by the coach in order to achieve the ain technical objectives. In fact the frequency of skills perfored by each player is an iportant factor to develop their relationship with the ball and their technical copetences in gae. Therefore, according to Kelly and Drust (2009), field size ay alter a nuber of iportant technical skills required for atch-play. Table 4. Studies that analyzed the technical ipact of field size Kelly & Drust (2009) Casaichana & Castellano (2010) x x x x 44 Structure n Pass or control and pass Receive Dribble or control and dribble Shot or control and shoot Interception 4 x 4in ± 70 ± 180 ± 50 ± 85 ± 38 4 x 4in 8 ± 100 ± 180 ± 60 ± 60 ± 40 4 x 4in ± 80 ± 140 ± 57 ± 44 ± 38 8 in 14.5 ± ± ± ± in ± ± ± ± in 18.7 ± ± ± ± 1.5 At Owen, Twist and Ford (2004) study, results showed that enlarging the field diensions used for the sall-sided gae by 10 eters had no effect on the technical actions the players perfored. However, according to the sae authors, this finding ay have been confounded by the change in nuber of players. On Kelly and Drust (2009) study, the saller field results at increased pressure fro the opponents and this situation requires fro the players to dribble the ball ore often in order to avoid the opponent s pressure and overtake the. The field diensions can decrease or increase the distance aong players. These distances ay deterine the frequency of technical skills perfored by the players. Generally, studies showed that the field with ore diensions increase the nuber of events per players, i.e., increases the technical events at the atch. Exeplifying, ore distances aong players of the sae tea can help they in order to pass the ball to the teaates, because the opponents are ore distanced of the player with ball possession. In the case of less field diension the less distance aong teaates help to pass the ball but can restrict the efficient of the pass because the opponents are closer to the teaates and, consequently, closer to the take the ball. Therefore the field size needs to be correctly adapted according to ain goal of the coach. Consequently, according to the authors, the size of the field largely deterines players behaviors in sall-sided soccer gaes (Casaichana & Castellano, 2010). Therefore is iportant to ephasize that the coach need to consider the technical level of the players before design the exercise, i.e., technical level is an iportant factor that contribute to iprove the effectiveness of the sall-sided gae. Players with less technical level, possibly, need to play with high field diensions in order to iprove the technical events per atch and the tactical positioning on the field. On the other hand, players with high technical level ay play with ore nuber of players and less field diensions. Consequently, variables as field diensions and nuber of players need to be carefully consider before the application, in order to prescript the adequate exercise to the real needs of players. 99

8 Effects of the Goals Task Task constraints are an iportant factor that can be used to anipulate the relationship aong perforer-environent interactions towards an intended outcoe (Araújo, Davids & Hristovski, 2006). Constraints can restrict or enable ultiple behaviors that the syste can adopt (Davids, et al., 2008). Specifically, task constraints can help the players to center the perception to specific inforation. Therefore, they include the rules that constrain spatial and teporal patterns of the oveent dynaics during an activity that ay be open to interpretation (Handford, et al., 1997). In addition to constraints related to the field size or nuber of players per exercise, there are other conditions that ay be used in order to enhance the task and their objectives. However these alternative fors are not being applied on assive for. Nevertheless, soe studies analyzed tasks constraints effects at physiological and technical level. Table 5. Studies that analyzed the physiological and kineatical ipacts of goals task Mallo & Navarro (2008) Hill- Haas, Rowsell, Dawson & Coutts (2009) 1) 2) 3) 2 v 2 C 2 v 2 I C I C I x x x x 37 Structure n Heart Rate 5 in 5 in 5 in 2 4 x 6 in 2 4 x 6 in 2 4 x 6 in ± 9 b- in ± 9 b- in ± 11 b- in ± 1 on continuous sall sided gaes and 84 ± 1 on interittent sall sided gaes Distance Covered Total Walking Jogging Sprinting 747 ± ± ± ± 18 on continuous sall sided gaes and 2621 ± 19 on interittent sall sided gaes 1143 ± 10 on continuous sall sided gaes and 1150 ± 10 on interittent sall sided gaes 975 ± 25 on continuous sall sided gaes and 950 ± 22 on interittent sall sided gaes 417 ± 13 on continuous sall sided gaes and 444 ± 15 on interittent sall sided gaes 1) 3-a-side gae with the ai of keeping the ball in possession as uch tie as possible 2) 3-a-side gae with 2 outer players that can pass the ball to a player fro the tea that it as received fro 3) 3-a-side gae with goalkeepers (+2) At Mallo and Navarro (2008) the coparison of the deands on the players during the three exercises shows than the inclusion of a goalkeeper odified the physical and tactical behavior of the players. In fact, results shows statistical differences between exercise with goalkeeper and two exercises without goalkeeper, where the task with goalkeeper shows less intensity at heart rate and distance covered by players. According to Mallo and Navarro (2008) when playing with goalkeepers, the players tried to organize defensively their tea in order to protect their goal, which had a repercussion in the gae tie. On Hill-Haas, Rowsell, Dawson and Coutts (2009) study, authors analyzed the ipact of continuous and interittent exercise on the sae sub-phase in order to understand if the recovery tie provides differences at physiological levels. Results shows that interittent exercises raised significantly ore oderate and higherspeed running coparing to continuous sall-sided soccer gae. According to Hill-Haas et al (2009), one possible explanation for the greater frequency of sprint activity during interittent sall-sided soccer gaes was the additional passive rest period between each gae that ay have allowed for greater physiological recovery. Based on scoring ode on sall sided soccer gaes ( without goalkeepers on 25 x 15 eters during 15 inutes by each condition), Duarte et al (2010) anipulated three conditions (i.e., task constraints) in their study: i) line goal, scoring by dribbling past an extended line; ii) double goal, scoring in either of two lateral goals; and iii), central goal, scoring only in one goal. Their results suggested that heart rate variability associated with the line goal task constraint is lower than that associated with both double goal and central goal constraints (Duarte, et al., 2010). Therefore, according to authors, these effects represent a ore cardiovascular standardized stiulation of the players involved in the line goal task

9 The encourageents provided by the coaches ay influence directly the physiological indicators of the players Hoff, et al., 2002; Rapinini, et al., 2007). These effects ay be very iportant on real application to the training because the external otivation provided by coach supervision can perit achieve greater physiological gains Coutts, Murphy & Dascobe, 2004; Mazzetti, et al., 2000). Table 6. Studies that analyzed the technical ipact of goals task Structure n Ball Contacts Short distance passes Technical Events Errors in short distance passes Shots on goals 1) 5 in 20.8 ± ± ± 4.7% 0 20 Mallo & 2) 5 in ± ± ± 2.9% 0 Navarro (2008) 20 3) 5 in 12.3 ± ± ± 5.1% 1.3 ± ) 3-a-side gae with the ai of keeping the ball in possession as uch tie as possible 2) 3-a-side gae with 2 outer players that can pass the ball to a player fro the tea that it as received fro 3) 3-a-side gae with goalkeepers (3 vs 3+2) At Mallo and Navarro (2008) study, results showed that the constraint to keep the ball in possession the ost tie as possible increase the ball contacts by players at the sall-sided soccer gae. At the sae tie, this instruction increase the short distances passes. Consequently, the nuber of technical events can be influenced by different task constraints and, for this reason, coach need to create specific goals task in order to increase the possibility to develop the technical coponents of players. Conclusion The ain goal of this paper was to show the real iportance of sall-sided soccer gae for the coaches. Globally, studies showed the real iportance of anipulate factors as nuber of players or field diensions on sall-sided soccer gaes, odifying physiological, kineatical and technical indicators. In fact, literature suggests that ay vary the constraints as field diensions or nuber of players, prooting statistical differences aong sall-sided soccer gaes. Therefore coaches before ipleent the exercises and their task constraints, need to consider the level of players and the context in order to iprove the ain goals for specific players. Consequently, coach need to consider, in first instance, the ain goal of exercise and, after this consideration, anipulate the constrains that iprove the effectiveness of exercise. References Aroso, J., Rebelo, A. N., & Goes-Pereira, J. (2004). Physiological ipact of selected gae-related exercises. Journal of Sports Sciences, 22, 522. Araújo, D., Davids, K., & Hristovski, R. (2006). The ecological dynaics of decision aking in sport. Psychology of Sport and Exercise, 7(6), Balso, P. (1999). Precision football. Kepele, Finland: Polar Electro Oy. Bangsbo, J. (1994). The physiology of soccer with special reference to intense interittent exercise. Acta Physiologica Scandinavica, 619, Bopa, T. (1983). Theory and ethodology of training. Dubusque, Iowa: Kendall/Hunt. Casaichana, D., & Castellano, J. (2010). Tie-otion, heart rate, perceptual and otor behaviour deands in sall-sides soccer gaes: Effects of field size. Journal of Sports Sciences, 28(14), Coutts, A. J., Murphy, A. J., & Dascobe, B. J. (2004). Effect of direct supervision of a strength coach on easures of uscular strength and power in young rugby league players. Journal of Strength and Conditioning Research, 18, Davids, K., Button, C., & Bennett, S. (2008). Dynaics of Skill Acquisition: A Constraints-Led Approach. Chapaign: Huan Kinetics. Dellal, A., Chaari, K., Pintus, A., Girard, O., Cotte, T., & Keller, D. (2008). Heart Rate Responses During Sall-Sided Gaes and Short Interittent Running Training in Elite Soccer Players: A Coparative. Journal of Strength and Conditioning Research, 22(5),

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