Several time motion analysis studies have detailed

Transcription

1 EFFECTS OF A PERIODIZED SMALL-SIDED GAME TRAINING INTERVENTION ON PHYSICAL PERFORMANCE IN ELITE PROFESSIONAL SOCCER ADAM L. OWEN, 1 DEL P. WONG, 2 DARREN PAUL, 3 AND ALEXANDRE DELLAL 4 1 Sports Science Department, Rangers Football Club, Glasgow, Scotland; 2 Department of Health and Physical Education, The Hong Kong Institute of Education, New Territories, Hong Kong; 3 Aspetar, Qatar Orthopaedic and Sports Medicine Hospital, Doha, Qatar; and 4 Olympic Lyon FC (Soccer), Lyon, France ABSTRACT Owen, AL, Wong, DP, Paul, D, and Dellal, A. Effects of a periodized small-sided game training intervention on physical performance in elite professional soccer. J Strength Cond Res 26(10): , 2012 The present study examined effects of periodized small-sided game (SSG) training intervention during a 4-week in-season break on physical performance changes (i.e., speed, aerobic performance, and repeated sprint ability) within elite European soccer players. Fifteen, elite, male, professional players (age: years; height: cm; body mass: kg; _VO 2 max: mlkg 21 min 21 ) from a Scottish Premier League team participated in 7 separate SSG sessions (3 vs. 3 plus goalkeepers) of which games lasted for a 3-minute duration for selected number of games (ranged from 5 to 11) increasing over intervention period. To examine effects of SSG intervention on physical performance changes, pre- and posttesting sessions took place over a 2-day period (day 1: anthropometry and repeated sprint ability [RSA] assessments; day 2: running economy [RE] and blood lactate assessments). Results show that 4-week SSG training intervention induced significant improvement in RSA as indicated by faster 10-m sprint time (p, 0.05, small effect), total sprint time (p, 0.05, medium effect), and smaller percentage decrement score (p, 0.05, medium effect). Furrmore, SSGs also led to an improvement in RE as indicated through significantly reduced _ VO 2 and heart rate at running speed 9, 11, and 14 kmh 21 (all p s, 0.05, large effects). In conclusion, present study demonstrates that implementing a periodized SSG training intervention during 4-week in-season break is capable of improving elite-level soccer players physical fitness characteristics. Being able to Address correspondence to Adam Owen, adamleeowen@rangers.co.uk. 26(10)/ Ó 2012 National Strength and Conditioning Association develop physical characteristics in conjunction to technical and tactical elements of game, within a relatively short period, makes SSGs an appealing proposition for fitness coaches, players, and technical coaches alike. KEY WORDS football, fitness training, aerobic, repeated sprint ability, periodization, specific INTRODUCTION Several time motion analysis studies have detailed activity profiles of professional soccer match play (1,12). The consensus of reports shows outfield players to cover an average distance of 9 to 12 km during a game, according to different positional roles (9). Although prevalence of low-intensity activity experienced during match play elicits a greater reliance on aerobic metabolism (32), this is often interspersed with important bouts of high-intensity activity and sprinting (3,9) that coincide with decisive moments of game (i.e., tackles, passes, and shots) (25). Competing within elite level of sport, professional soccer players are expected to possess well-developed physical capabilities complementing technical and tactical demands of contemporary soccer (21). In particular, superior aerobic capacity (4), muscular strength, power (41), and repeated sprint ability (RSA) could be critical components to combat limited ball contacts encountered during match play, as reported for central defenders and central attacking midfielders competing in English and Spanish first division (9). However, a congested schedule, as is often found among soccer s elite clubs, often makes it problematic for coaches attempting to simultaneous integrate se different training parameters (25). The supposition that small-sided games (SSGs) may simulate physiologic workloads and intensities commensurate of actual match play while also developing technical and tactical proficiency has led to its popularity as a training modality in applied and scientific domain within recent years (7,10,11,20,28). Specifically, from an applied perspective, potential to increase aerobic capacity with regular 2748

2 ball involvement may satisfy sport scientist, coach, and players demands, thus highlighting its advantages over generic training methods such as interval running training. However, manipulating pitch size, number of games played, duration, coach encouragement, and technical restrictions have been shown to severely alter physical and technical demands associated with SSG (7,10,11,20,31). In relation to se findings, it is of paramount importance that session design and SSGs implementation should be performed with precision and careful consideration of training objective (18,34). Conversely, scientific evidence supporting SSG as a useful training modality has shown cardiovascular stress and training adaptations comparative to generic short-duration intermittent running training (8,26). Previous research conducted with Norwegian first division players concluded that SSGs could induce a steady-state exercise intensity of 91% of maximal heart rate (HRmax), corresponding to about 85% of maximal oxygen uptake ( _ VO 2 max) (24). Studies have also shown SSG to elicit similar effects on aerobic capacity than 7 weeks of generic training in preseason (18) or 6 or 12 weeks of interval training in youth players during a competitive season (26,33). However, re seems a paucity of data pertaining to effects of SSG on physical parameters or than maximal aerobic capacity. Moreover, claims of SSGs do not simulate high-intensity repeated sprint demands of elite-level soccer that have been confined to female soccer players (14) and warrants furr scrutiny to wher SSG can actually improve RSA test performance in elite male soccer players. The aim of present study was to examine effects of a 4-week SSG (3 vs. 3 + GKs) training intervention over 7 sessions on physical performance (i.e., speed, aerobic performance, and repeated sprint ability) of elite male soccer players during in-season break. It was hyposized that an SSG training intervention would induce a greater increase of repeated sprint ability and sprint performance than increases on aerobic capacity. The findings could potentially provide valuable information to coaches for design and promotion of use of SSGs as part of a periodized conditioning program within elite-level soccer, especially during in-season break. METHODS Experimental Approach to Problem To examine changes in physical performance after 4-week periodized SSG training intervention, all players were tested during 2 sessions, 4 weeks apart (i.e., pre- and posttests) (Table 1). The study was conducted during in-season break with players not involved within competitive fixtures over this period. The shutdown in fixtures over intervention training period (4 weeks from start to finish) was because of a combination of poor wear, international fixtures, and a reserve team fixture break (for nonplaying squad players). The structured periodized training intervention was able to be controlled at this specific period of season to a greater level than normal because of this nonscheduled fixture break. This period was not designed as a recovery period as domestic league does not have a scheduled mid-season break but because of cancellation of fixtures/international breaks and nonselected players, it was an opportunity to run intervention. Testing sessions took place over a 2-day period at same time of day to eradicate potential effects of any circadian variation on participants (day 1: anthropometry and repeated sprint ability assessments and day 2: running economy (RE) and lactate assessments). After pretest, 7 SSG training intervention sessions (each lasting minutes incorporating warm-up, low-intensity technical work, SSG sessions, and cooldown) were performed within 4-week periodized program. In addition to SSGs, players performed technical tactical sessions and some injury prevention exercises during study period. However, se sessions (heart rate [HR], 85% of HRmax) were not deemed as intense enough to induce any significant changes on player s physical profile over a 4-week period. All players were fully familiarized with experimental procedures and requirements of games before present study because of testing and training protocols being used within club as part of its sports science and conditioning structure. TABLE 1. Four-week periodized training intervention.* Monday Tuesday Wednesday Thursday Friday Saturday Sunday Week 0 Pretest Rest Pretest Day off Week 1 Tech + tact SSGs 1 + IP LITr Tech + tact SSGs 2 + IP LITr Day off Week 2 Tech + tact SSGs 3 + IP LITr Tech + tact SSGs 4 + IP LITr Day off Week 3 Tech + tact SSGs 5 + IP LITr Tech + tact SSGs 6 + IP LITr Day off Week 4 SSGs 7 + IP Tech + Tact LITr Posttest Rest Posttest Day off *IP = injury prevention/activation (low-intensity work); LITr = low-intensity recovery session; SSGs = small-sided games; Tact = tactical session (low intensity); Tech = technical session (low intensity). VOLUME 26 NUMBER 10 OCTOBER

3 Effect of Small-Sided Games on Physical Performance TABLE 2. SSG training intervention.* Session progression Progressive overload Total SSG duration (min) SSGs min games 15 SSGs min games 18 SSGs min games 21 SSGs min games 24 SSGs min games 27 SSGs min games 30 SSGs min games 33 *All SSGs were played in a 3 versus 3 format (3 outfield players + 1 goalkeeper on each side) for a 3-minute duration and a 2-minute passive recovery between bouts. Subjects Fifteen, elite, male, professional soccer players (age: years; height: cm; body mass: kg; _VO 2 max: mlkg 21 min 21 ; and sum of 8 skinfold sites: mm) from a Scottish Premier League team volunteered for investigation. Written informed consent was received from all players after a brief but detailed explanation about aims, benefits, and risks involved with this investigation. Players were told y were free to withdraw from study at any time without penalty. The study was conducted according to Declaration of Helsinki, and protocol was fully approved by Sports Science Department at Rangers Football Club before commencement of assessments. The players had refrained from vigorous high-intensity exercise 24 hours before testing sessions. During study, all players were instructed to maintain normal daily food and water intake and no dietary interventions were undertaken. The training sessions performed pre intervention were general football training sessions (inclusive of low-, moderate-, and high-intensity training sessions) depending on training week and fixture calendar. The players involved within this study would have generally performed some strength (low-level prevention sessions), tactical, technical (low intensity sessions), and conditioning sessions (inclusive of RSA activities and aerobic intervals). During 4-month buildup to start of intervention, players involved within study had played a combination of reserve team games, first team games, and generic football training. Anthropometrical Assessment The anthropometric measurements included height, body mass, and summation of 8 skinfold sites using Harpenden calipers (biceps, triceps, subscapular, iliac crest, supraspinale, abdominal, midthigh, and calf) to determine body fat level (29). Repeated Sprint Ability Assessments After a standardized warm-up, which involved running at 10 kmh 21 at 70% HRmax for 10 minutes followed by 5- minute bursts of self-selected running and stretching, players performed RSA assessment consisting of m maximal sprints, with a 25-second active recovery period to walk back to start (15). The sprint time was measured using photocells (0.01-second precision; Brower Timing Systems, UT, USA) placed at start, 10, and 20 m at height of 1 m. The players started 0.7 m behind starting gate. Repeated sprint ability was analyzed by 3 methods: (a) fastest sprint time (FST) among sprints, (b) total sprint time (TST), and (c) percentage decrement score (%Decre). The TST was used as it has been recommended by previous study of RSA in soccer players (44). The %Decre was selected as it was recently reported as most valid and reliable method of quantifying fatigue in RSA test (16). Concerning FST of 20 m, associated 10-m split time was also selected for analysis. TABLE 3. Effects of SSG training on fitness parameters (n = 15). Pre Post 95% CI Effect size/magnitude RSA, s 10-m FST * /small 20-m FST /small TST * /medium %Decre * /medium Skinfold thickness, mm * /trivial CI = confidence interval; FST = fastest sprint time; RSA = repeated-sprint ability; TST = total sprint time; %Decre = percentage decrement score. *p, Submaximal Treadmill Test Before commencing treadmill test, each player performed a 5-minute jogging warm-up on motorized treadmill (Technogym, Run 500 model, Italy) at a velocity that elicited approximately 60% of player s HRmax, which was obtained from player s previous maximal treadmill test. Thereafter, players performed 5 minutes of individually selected stretching exercises. After this warmup, each player performed a submaximal running test at 3% gradient for 3 individual 3- minute running stages (stage 1: 2750

4 TABLE 4. Effects of SSG training on submaximal aerobic performance (n = 15). Pre Post 95% CI Effect size/magnitude _VO 2,mlmin 21 kg 21 9kmh 21, 3% * 0.37 to /large 11 kmh 21, 3% * 0.98 to /large 14 kmh 21, 3% * 0.65 to /medium RER 9kmh 21, 3% to /trivial 11 kmh 21, 3% to /trivial 14 kmh 21, 3% to /medium RR 9kmh 21, 3% to /small 11 kmh 21, 3% * 1.67 to /small 14 kmh 21, 3% * 0.02 to /small HR, bmin 21 9kmh 21, 3% * to /large 11 kmh 21, 3% * to /large 14 kmh 21, 3% * 4.95 to /large Blood lactate, mmoll to /trivial CI = confidence interval; HR = heart rate; RER = respiratory exchange ratio; RR = respiratory rate; _ VO 2 = oxygen uptake. *p, kmh 21 ; stage 2: 11 kmh 21 ;andstage3:14kmh 21 ). HR responses (Polar Team System, Kempele, Finland), oxygen uptake ( _ VO 2 ) (Medgraphics, London, United Kingdom), respiratory exchange ratio (RER), respiratory rate (RR), and blood lactate samples were taken at last 15 seconds of each exercise stage. Capillary blood samples were withdrawn from players thumb and analyzed for whole blood lactate using an Analox GM7 analyzer (Analox Instruments, London, UK). The _ VO 2 value obtained at end of each stage from this test represented RE of players. Small-Sided Game Training Intervention All games were preceded by a standardized warm-up of 12 minutes followed by a 3-minute passive recovery. During this period, players were informed to only consume water if needed. All games were carried out on an outdoor grass field with an average temperature of C. The SSGs consisted of teams of 3 outfield players plus a goalkeeper being played on a m pitch (area per player = 125 m 2 ) for a 3-minute duration for selected number of games increasing over intervention period (Table 2). No specific tactical conditions were placed on players within games, and a large number of soccer balls were placed in each net with play always starting with goalkeepers when ball went out of play to aid in a rapid continuation of play. Statistical Analyses Data are expressed as mean 6 SD. The normal distribution of datawascheckedusing Kolmogorov-Smirnov test. After confirming normal distribution, paired sample t-test was used to compare difference between pre- and posttest. Significant level was defined as p # Effect size (Cohen s d) was calculated to determine practical difference between SSG and large-sided games. Effect size values of 0 to 0.19, 0.20 to 0.49, 0.50 to 0.79, and 0.8 and above were considered to represent trivial, small, medium, and large differences, respectively (5). RESULTS There was a trivial effect of SSG training on skinfold thickness (Table 3). Concerning RSA, 4 weeks of SSGs induced significant improvement in RSA as indicated by faster 10-m FST (p, 0.05, small effect, Table 3), TST (p, 0.05, medium effect), and smaller %Decre (p, 0.05, medium effect). Concerning submaximal aerobic performance (Table 4), 4 weeks of SSG training significantly reduced _ VO 2 at running speed of 9 (p, 0.05, large effect), 11 (p, 0.05, large effect), and 14 kmh 21 (p, 0.05, medium effect). Moreover, it also significantly lowered HR responses at running speed of 9, 11, and 14 kmh 21 (all p s, 0.05, large effects). There were small to trivial effects on RER, RR, and blood lactate (La) after 4 weeks of small-sided training games. DISCUSSION The aim of present study was to investigate effect of a 4-week SSG training intervention on physical fitness performance measures in elite, adult, professional, soccer players during in-season break. The main findings revealed that training intervention significantly improved players repeated sprint ability, sprint performance (TST and VOLUME 26 NUMBER 10 OCTOBER

5 Effect of Small-Sided Games on Physical Performance %Decre, Table 3), and RE, which is presented as a reduced _VO 2 and HR when running at submaximal levels of 9, 11, and 13 kmh 21 (Table 4). It appears from our findings, that periodized SSG training intervention could have a positive effect on both anaerobic and aerobic system during in-season break. The findings from present study add to emerging paradigm of research that has identified SSG as an alternative training modality to generic drills (e.g., interval running training) capable of improving physical fitness characteristics in elite senior soccer players. Corroborative studies have shown a 7-week preseason training period of SSG to significantly improve Yo-Yo intermittent recovery test performance, although not _ VO 2 max (18), while a 3% improvement in RE has been found in youth players after 12 (4 weeks preseason and 8 weeks in-season) weeks of SSG (26). Despite similar trends being shown, it would seem futile to compare results from present study to those previously conducted, particularly given that metabolic and physical stressors have shown to vary greatly when manipulating SSG training variables (e.g., pitch dimensions, number of players, coach encouragement) and subsequent differences in research methodologies innate within literature. The inclusion of an RSA test as a measure of performance in applied and research domain is substantiated by reported similarities of its physiological characteristics with high-speed sprinting performed during actual match play (31). Performing repetitive sprint efforts, change of direction, kicking, tackling, and dribbling are characteristics likely to severely exacerbate physiologic strain during SSG. Yet this may offer an auxiliary physical stimulus because ability to perform technical and tactical requirements under fatigued conditions is considered important for soccer (25). In addition, despite repeated sprinting drills and interval training ( seconds at 120% of maximal aerobic speed) shown to concurrently improve sprint, vertical jump, _ VO2, and RSA during preseason and in-season training (13,43), such drills do not offer motivation or enjoyment for players compared with those including a ball and failing to imitate unorthodox movements commonly associated with SSG (20), furr limiting any comparisons. As a result, present study is unique as it revealed a 4-week periodized program of SSGs (3 vs. 3) that improved measures of RSA and RE during mid-phase of season at an elite level of professional soccer. The ability to recover from intense bouts of repeated sprint effort is deemed critical during intermittent sports such as soccer and can be facilitated by a superior aerobic energy system (2). During recovery phase, _ VO2 is elevated to restore metabolic processes to preexercise conditions. The adaptations associated with an increased level of aerobic fitness may facilitate recovery process and subsequent sprint performance by providing aerobically derived energy at a faster rate during recovery period (38,39). Possessing an elevated aerobic capacity is also associated with adjunct higher glycogen stores necessary for energy release during intense bouts of activity (21). The benefits of an 11% improvement of _ VO2 max found in youth soccer players has shown to culminate in greater involvement with ball, total distance covered, and a 100% increase in number of sprints performed during match play (36). Research has also shown a high aerobic capacity to be correlated with RSA (2) and team success (42), thus furr advocating advantages of a superior _ VO 2 max. On attaining a good aerobic base, any furr changes in fitness level experienced during season may be better detected through submaximal indices of aerobic fitness, such as RE and corresponding blood lactate concentration (26). Running economy may differ as much as 20% between individuals with similar _ VO 2 max (6), attributed to, among or factors, mechanical and neuromuscular skill, storage of elastic energy, and anatomical traits (35). Impellizzeri et al. (26) found SSG to be equally as effective as training without ball in improving RE and _ VO 2 max. Also, potential training effect of SSG and interval training has shown to lower HR (by 9 bmin 21 )at7kmh 21 and subsequently improve RE by 14% at this speed (4). The greater gains found in study by Chamari et al. (4) might be because of different baseline fitness levels of participants. Decreasing energetic cost at a sustained workload may culminate in a reduced oxygen demand that may allow players to eir exercise at a lower HR or similar HR but with greater intensity (19). Theoretically, an approximately 5% improvement in RE could decipher an extra 1,000 m covered during a soccer match (37). All of which could be considered desirable characteristics during 90 minutes of physically exertive match play. Neverless, in present study, significant improvement in RE ( %) shows that SSGs are comparable to results achieved through strength training (22,23) in development of RE. Yet despite present findings advocating RE as a sensitive measure of fitness during mid-stage of season, it is questionable wher se improvements are transferable to work economy and specific soccer movements such as high-speed sprinting, arced runs, or change of direction (17). Furrmore, it would be injudicious to suggest that improved RE would equate to a concomitant increase in players _ VO2 max. Because intensity of SSG can be severely altered by manipulating exercise type, field dimensions, coach encouragement, and number of players involved (31,40), present study reaffirms necessity for fitness coaches to carefully consider training objective when implementing SSG drills. For example, influence number of players can have on intensity is highlighted by research showing configurations of 3-a-side to elicit a lower blood lactate response comparable to SSGs comprising even fewer players (e.g., 1 vs. 1 and 2 vs. 2) (27). Rampinini et al. (31) found intraparticipant variability to be much greater for blood lactate concentration than mean HR during high-intensity bouts of SSG. This emphasizes need to standardize coach 2752

6 encouragement to improve reproducibility between different bouts and sessions of SSG. The same study by Koklu et al. (27) also showed HR and %HRmax to be greater during 3- and 4-a-side than games of 1- and 2-a-side. Correspondingly, greater HR values have been shown during SSG of 3 vs. 3 compared with 5 vs. 5 (30). Platt et al. (30) suggested that this may be because of greater total distance covered, high-intensity activity, tackling, dribbling passing, and goal attempts encountered during 3-a-side game. Regardless, it seems that exercising at intensities close to or above 90% of HRmax is required to improve aerobic fitness in highly trained soccer players (37). The present study was conducted during mid-phase of season and comprised players not involved in competitive fixtures but still engaged in training. Admittedly, lack of control group debilitates findings and it could be argued that gains in physical performance, as measured by RSA and RE, were attributed to technical and tactical elements of training during intervention period. However, it is worth noting that SSGs were only high-intensity sessions (e.g.,.90%hrmax) performed during this period. Therefore, it can be inferred that physical improvements exhibited during a 4-week within-season SSG training intervention may culminate in greater fitness levels of physical qualities displayed during actual competitive match play. PRACTICAL APPLICATIONS The present study demonstrates that implementing a 4-week periodized SSG training intervention can improve physical fitness characteristics of elite professional soccer players during in-season break. Being able to develop physical profile of players, within a relatively short period, while encompassing technical and tactical elements, makes SSG an appealing proposition for fitness coaches, players, and coaches alike. Subsequently, ability to perform repeated sprints is considered important during intermittent sports such as soccer, and ability to improve repeated sprint ability during soccer-specific games can positively promote need to integrate SSGs as part of elite soccer clubs in-season conditioning program instead of generic nonspecific drills or sessions, when re is no official match scheduled. Despite potential advantages of SSG, care should be considered when implementing this training method in a periodized program. An overreliance on this training method may mask specific weaknesses within a player s profile and requires stringent control and standardization of influential factors (e.g., duration, pitch sizes) to avoid potential overtraining effects. The practical implications may be furr enhanced by quantifying optimal load and intensities of SSG alongside or forms of training that more specifically represents day-to-day activity within a professional soccer club. In addition, in-season training load should be monitored to prevent players from overreaching and overtraining. Coaches could use SSGs during in-season break to continually develop physical, technical, and tactical components of game in conjunction to each or rar than in isolation. ACKNOWLEDGMENTS Results of present study do not constitute endorsement of product by authors or National Strength and Conditioning Association. REFERENCES 1. Bangsbo, J. The physiology of soccer With special reference to intense intermittent exercise. Acta Physiol Scand Suppl 619: 1 155, Bishop, D, Edge, J, and Goodman, C. Muscle buffer capacity and aerobic fitness are associated with repeated sprint ability in women. Eur J Appl Physiol 92: , Bradley, PS, Sheldon, W, Wooster, B, Olsen, P, Boanas, P, and Krustrup, P. High intensity running in English FA Premier League soccer matches. J Sports Sci 27: , Chamari, K, Hachana, Y, Kaouech, F, Jeddi, R, Moussa-Chamari, I, and Wisloff, U. Endurance training and testing with ball in young elite soccer players. Br J Sports Med 39: 24 28, Cohen, J. Statistical Power Analysis for Behavioral Sciences. Hillsdale, NJ: Erlbaum Associates, pp Daniels, JT. A physiologist s view of running economy. Med Sci Sports Exerc 17: , Dellal, A, Chamari, K, Owen, A, Wong, DP, Lago-Penas, C, and Hill-Haas, S. Influence of technical instructions on physiological and physical demands within small-sided soccer games. Eur J Sport Sci 11: , Dellal, A, Chamari, K, Pintus, A, Girard, O, Cotte, T, and Keller, D. Heart rate responses during small-sided games and short intermittent running training in elite soccer players: a comparative study. J Strength Cond Res 22: , Dellal, A, Chamari, C, Wong, DP, Ahmaidi, S, Keller, D, Barros, MLR, Bisciotti, GN, and Carling, C. Comparison of physical and technical performance in European professional soccer matchplay: The FA premier league and La LIGA. Eur J Sport Sci 11: 51 59, Dellal, A, Hill-Haas, S, Lago-Penas, C, and Chamari, K. Small-sided games in soccer: amateur vs. professional players physiological responses, physical and technical activities. J Strength Cond Res 25: , Dellal, A, Lago-Penas, C, Wong, DP, and Chamari, K. Effect of number of ball contacts within bouts of 4 vs. 4 small-sided soccer games. Int J Sports Physiol Perform 6: , Di Salvo, V, Gregson, W, Atkinson, G, Tordoff, P, and Drust, B. Analysis of high intensity activity in premier league soccer. Int J Sports Med 30: , Dupont, G, Akakpo, K, and Berthoin, S. The effect of in-season, high-intensity interval training in soccer players. J Strength Cond Res 18: , Gabbett, TJ and Mulvey, MJ. Time-motion analysis of small-sided training games and competition in elite women soccer players. J Strength Cond Res 22: , Girard,O,Mendez-Villanueva,A,andBishop,D.Repeated-sprintabilitypart I: Factors contributing to fatigue. Sports Med 41: , Glaister, M, Howatson, G, Pattison, JR, and McInnes, G. The reliability and validity of fatigue measures during multiple-sprint work: An issue revisited. J Strength Cond Res 22: , Helgerud, J, Engen, LC, Wisloff, U, and Hoff, J. Aerobic endurance training improves soccer performance. Med Sci Sports Exerc 33: , VOLUME 26 NUMBER 10 OCTOBER

7 Effect of Small-Sided Games on Physical Performance 18. Hill-Haas, SV, Coutts, AJ, Dawson, BT, and Rowsell, GJ. Time motion characteristics and physiological responses of small-sided games in elite youth players: influence of player number and rule changes. J Strength Cond Res 24: , Hill-Haas, SV, Dawson, B, Impellizzeri, FM, and Coutts, AJ. Physiology of small-sided games training in football: A systematic review. Sports Med 41: , Hill-Haas, S, Rowsell, GJ, Dawson, BT, and Coutts, AJ. Acute physiological responses and time-motion characteristics of two small-sided training regimes in youth soccer players. J Strength Cond Res 23: , Hoff, J. Training and testing physical capacities for elite soccer players. J Sports Sci 23: , Hoff, J and Helgerud, J. Maximal strength training enhances running economy and aerobic endurance performance. In: Football (Soccer). New Developments in Physical Training Research. J. Hoff and J. Helgerud, eds. Trondheim, Norway: Norwegian University of Science and Technology, pp Hoff, J, Helgerud, J, and Wisloff, U. Maximal strength training improves work economy in trained female cross-country skiers. Med Sci Sports Exerc 6: , Hoff, J, Wisloff, U, Engen, LC, Kemi, OJ, and Helgerud, J. Soccer specific aerobic endurance training. Br J Sports Med 36: , Iaia, FM, Rampinini, E, and Bangsbo, J. High-intensity training in football. Int J Sports Physiol Perform 4: , Impellizzeri, FM, Marcora, SM, Castagna, C, Reilly, T, Sassi, A, Iaia, FM, and Rampinini, E. Physiological and performance effects of generic versus specific aerobic training in soccer players. Int J Sports Med 27: , Koklu, Y, Asci, A, Kocak, FU, Alemdaroglu, U, and Dundar, U. Comparison of physiological responses to different small-sided games in elite young soccer players. JStrengthCondRes25: , Owen, A. Physiological & technical analysis of small-sided conditioned training games within professional football. Soccer J 49: 5, Owen, AL, Wong, DP, McKenna, M, and Dellal, A. Heart rate responses and technical comparison between small- vs. large-sided games in elite professional soccer. JStrengthCondRes25: , Platt, D, Maxwell, A, Horn, R, Williams, M, and Reilly, T. Physiological and technical analysis of 3 v. 3 and 5 v 5 youth football matches. Insight: FA coaches association Journal 4: 23 24, Rampinini, E, Impellizzeri, FM, Castanga, C, Abt, G, Chamari, K, Sassi, A, and Marcora, SM. Factors influencing physiological responses to small-sided soccer games. J Sports Sci 25: , Reilly, T. Energetics of high-intensity exercise (soccer) with particular reference to fatigue. J Sports Sci 15: , Reilly, T and Thomas, V. A motion analysis of work rate in different positional roles in pro football match-play. J Hum Mov Stud 2: 87 97, Reilly, T and White, C. Small-sided games as an alternative to interval training for soccer players. J Sports Sci 22: 559, Saunders, PU, Pyne, DB, Telford, RD, and Hawley, JA. Factors affecting running economy in trained distance runners. Sports Med 34: , Smaros, G. Energy usage during a football match. In: Proceedings of 1st International Congress on Sports Medicine Applied to Football. L. Vecciet, ed. Rome, Italy: D Guanillo, pp Stolen, T, Chamari, K, Castagna, C, and Wisloff, U. Physiology of soccer: An update. Sports Med 35: , Taoutaou, Z, Granier, P, Mercier, B, Mercier, J, Ahmaidi, S, and Prefaut, C. Lactate kinetics during passive and partially active recovery in endurance and sprint athletes. Eur J Appl Physiol Occup Physiol 73: , Tomlin, DL and Wenger, HA. The relationship between aerobic fitness and recovery from high intensity intermittent exercise. Sports Med 31: 1 11, Williams, K and Owen, A. The impact of player numbers on physiological responses to small sided games. J Sports Sci Med 6: , Wisloff, U, Castagna, C, Helgerud, J, Jones, R, and Hoff, J. Strong correlation of maximal squat strength with sprint performance and vertical jump height in elite soccer players. Br J Sports Med 38: , Wisloff, U, Helgerud, J, and Hoff, J. Strength and endurance of elite soccer players. Med Sci Sports Exerc 30: , Wong, PL, Chaouachi, A, Chamari, K, Dellal, A, and Wisloff, U. Effect of preseason concurrent muscular strength and high-intensity interval training in professional soccer players. J Strength Cond Res 24: , Wong, PL, Lau, PW, Mao, DW, Wu, YY, Behm, DG, and Wisloff, U. Three days of static stretching within a warm-up does not affect repeated-sprint ability in youth soccer players. J Strength Cond Res 25: ,