Tests of physical qualities are used to measure an

RELATIONSHIP BETWEEN TESTS OF PHYSICAL QUALITIES AND PHYSICAL MATCH PERFORMANCE IN ELITE RUGBY LEAGUE PLAYERS TIM J. GABBETT, 1,2 JOSH G. STEIN, 1 JUSTIN G. KEMP, 3 AND CHRISTIAN LORENZEN 3 1 School of Exercise Science, Australian Catholic University, Brisbane, Australia; 2 School of Human Movement Studies, The University of Queensland, Brisbane, Australia; and 3 School of Exercise Science, Australian Catholic University, Melbourne, Australia ABSTRACT Gabbett, TJ, Stein, JG, Kemp, JG, and Lorenzen, C. Relationship between tests of physical qualities and physical match performance in elite rugby league players. J Strength Cond Res 27(6): 1539 1545, 2013 Previous investigators have reported significant relationships between tests of physical qualities and physical match performance in high-intensity, intermittent team sport (e.g., soccer) players. Although rugby league requires competitors to perform high-intensity running, unlike most or highintensity intermittent team sports, physical demands are significantly increased through large amounts of tackling, wrestling, and grappling that players are required to perform during match play. This study investigated relationship between tests of physical qualities and match performance in professional rugby league players and determined wher running capacities were associated with collision and repeated high-intensity effort demands of match play. Thirty-eight elite rugby league players (mean 6 SD, age,23.16 2.7 years) performed tests of repeated sprint ability (12 3 20-m sprints on a 20-second cycle), prolonged high-intensity intermittent running ability (8 3 12-second shuttle sprints on a 48-second cycle), and estimated maximal aerobic power (VȮ 2 max) (multistage fitness test). Global positioning system data were collected during 16 professional rugby league matches. Players with better, prolonged, high-intensity intermittent running ability covered greater total distance and greater distance in high-speed running during match play. However, inconsistent relationships were found between tests of running abilities and or match performance variables, with prolonged high-intensity running ability (negative), VȮ 2 max (positive), and repeated-sprint ability (no relationship) differentially associated with total number of collisions and repeated high-intensity effort bouts Address correspondence to Dr. Tim J. Gabbett, tim_gabbett@yahoo.com.au. 27(6)/1539 1545 Ó 2013 National Strength and Conditioning Association performed in competition. These findings demonstrate importance of prolonged high-intensity running ability to match running performance of elite rugby league players but also highlight need for game-specific conditioning to prepare players for high-intensity collision and repeatedeffort demands of game. KEY WORDS physical attributes, fitness, collision sport, training INTRODUCTION Tests of physical qualities are used to measure an athlete s fitness, training progression, and preparedness for competition. Several researchers have explored relationship between tests of physical qualities and physical match performance in highintensity intermittent team sports (3,4,17,21,23). Rampinini et al. (21) investigated relationship between tests of physical qualities and physical match performance in professional soccer players. Players with better performance on a repeated-sprint test covered greater match distances at very high speed running and sprinting. Better performance on an incremental field test was also associated with greater total distance, high-intensity running, and very high intensity running during match play. Castagna et al. (3) and Krustrup et al. (18) found that players with better performance on Yo-Yo intermittent recovery test performed more running and high-intensity activity during match play in elite young male and female soccer players, respectively. These findings suggest a relationship between tests of physical qualities and physical performance during match play; better developed physical qualities generally lead to greater physical performance in soccer competition. Repeated-sprint ability is widely accepted as a critical component of high-intensity intermittent sports. However, in some team sports (e.g., rugby league and rugby union), athletes are required to perform multiple maximal effort sprints, tackles, and collisions, with very short recovery between efforts. Indeed, recent evidence from our laboratory (8,14) has shown that during professional rugby league VOLUME 27 NUMBER 6 JUNE 2013 1539

Fitness and Match Performance in Elite Rugby League match play, repeated-sprint bouts (defined as $3 sprints with minimal recovery between sprints) occurred infrequently (1 6 1 bout), whereas high-intensity repeated-effort bouts (defined as $3 sprints or tackles with minimal recovery between efforts) occurred regularly (9 6 1 bouts). Moreover, we have recently shown that repeated high-intensity effort exercise (sprinting and tackling) is associated with greater heart rate and perceived exertion and poorer sprint performance than repeated-sprint exercise alone (16), demonstrating that addition of tackling significantly increases physiological response to repeated-sprint exercise and has potential to reduce physical performance. Collectively, se findings suggest that performance of repeatedsprint training in isolation is likely to result in rugby league players being underprepared for repeated high-intensity effort (i.e., sprinting and tackling) demands of competition. Despite high collision demand, and importance of repeated high-intensity effort ability to rugby league performance, generic tests of physical qualities (e.g., repeated-sprint ability, prolonged high-intensity intermittent running ability, and maximal aerobic power) are commonly used to assess training adaptations and readiness to play (12,13). However, it is currently unclear wher se tests of physical qualities (which are all running based) adequately assess ability of players to perform repeated high-intensity effort and contact demands of competitive match play. With this in mind, purpose of this study was to investigate relationship between tests of physical qualities and match performance in professional rugby league players and determine wher running capacities were associated with collision and repeated high-intensity effort demands of match play. METHODS Experimental Approach to Problem This study investigated relationship between tests of physical (running) qualities and physical match performance in elite rugby league players using a prospective cohort experimental design. The match demands of elite rugby league players were compared by separating players into high fitness and low fitness groups based on ir performances in repeated-sprint ability, prolonged high-intensity intermittent running ability, and maximal aerobic power tests. In addition, relationship between physical qualities and physical match performance was determined using partial correlations. It was hyposized that physical test performance would be associated with running match demands but would not be associated with high-intensity collision and repeated-effort demands of match play. Subjects Thirty-eight elite rugby league players from a National Rugby League squad (mean 6 SD, age, 23.1 6 2.7 years) participated in this study. All participants received a clear explanation of study, including information on risks and benefits, and written consent was obtained. All experimental procedures were approved by Human Ethics Committee of University of Queensland. Fitness Testing Battery Players underwent fitness testing in February as part of ir preseason training program for forthcoming playing season. The physical tests performed were (a) repeatedsprint ability, (b) prolonged high-intensity intermittent running ability, and (c) estimated maximal aerobic power. All testing was conducted at same time of day (approximately 8.00 AM). Participants were requested to abstain from strenuous physical exercise for 72 hours before testing. Players were instructed to consume ir normal pretraining breakfast and to ensure adequate hydration at time of testing. Repeated-Sprint Ability Repeated-sprint ability was assessed using a repeated 20-m sprint test (13). Players performed 12 maximal effort sprints over a 20-m distance, with each sprint performed on a 20-second cycle. The players total sprint time was calculated and used as repeated-sprint score. The intraclass correlation coefficient for test-retest reliability and typical error of measurement for total repeated-sprint time was 0.91 and 1.5%, respectively. Prolonged High-Intensity Intermittent Running Ability The ability of players to repeat prolonged high-intensity running efforts was assessed using a repeated 12-second sprint-shuttle test (13). Players performed 8 3 12-second maximal effort shuttles (sprinting forward 20 m, turning 1808 and sprinting 10 m, turning 1808 and sprinting 20 m, etc.) with each shuttle performed on a 48-second cycle. Each test was filmed, with player s total distance calculated and used as prolonged high-intensity intermittent running ability score. The intraclass correlation coefficient for test-retest reliability and typical error of measurement for prolonged high-intensity intermittent running ability test was 0.91 and 4.3%, respectively. Maximal Aerobic Power Maximal aerobic power was estimated using multistage fitness test (22). Players were required to run back and forth (i.e., shuttle run) along a 20-m track, keeping in time with a series of signals on a compact disk. The frequency of audible signals (and hence, running speed) was progressively increased, until participants reached volitional exhaustion. The multistage fitness test was concluded if participants eir (a) voluntarily stopped test or (b) were unable to keep time with audible signals on at least 2 consecutive shuttles. Maximal aerobic power (VȮ 2 max) was predicted using regression equations described previously (22). When compared with treadmill-determined VȮ 2 max, it has been demonstrated that multistage fitness test provides a valid estimate of VȮ 2 max (22). In addition, intraclass correlation coefficient for test-retest reliability and typical error of measurement for multistage fitness test were 0.90 and 3.1%, respectively. 1540

TABLE 1. Physical qualities and match performance of players with well-developed ( high fitness ) and poorly developed ( low fitness ) physical qualities.* Repeated-sprint ability (s) Prolonged high-intensity intermittent running ability (m) Maximal aerobic power (ml$kg 21 $min 21 ) VOLUME 27 NUMBER 6 JUNE 2013 1541 High fitness Low fitness High fitness Low fitness High fitness Low fitness Test of physical quality 41.6 6 1.1 42.5 6 0.9 448.4 6 7.8 433.3 6 11.6 56.8 6 1.5 52.1 6 1.9 Match performance variable Total match time (min) 55.7 6 18.1 61.9 6 23.2 70.1 6 20.6 b 47.5 6 13.9 53.5 6 17.4 64.1 6 22.9 Total collisions (no.) 38.2 6 11.9 41.5 6 20.7 30.6 6 12.9 b 49.1 6 15.1 45.2 6 13.4 a 34.5 6 18.3 RHIE bouts (no.) 9.7 6 5.4 9.6 6 7.1 7.5 6 6.1 a 11.8 6 5.8 11.1 6 6.6 8.3 6 5.7 Total distance (m) 5377 6 1662 5959 6 2324 6800 6 1969 b 4535 6 1326 5170 6 1471 6165 6 2378 Low-speed distance (m) 4943 6 1543 5565 6 2153 6309 6 1852 b 4199 6 1200 4793 6 1387 5716 6 2202 High-speed distance (m) 434 6 133 392 6 198 490 6 141 b 336 6 159 377 6 99 449 6 212 Total Collisions (no. per min) 0.76 6 0.34 0.79 6 0.52 0.47 6 0.26 b 1.07 6 0.36 0.92 6 0.34 a 0.63 6 0.47 RHIE bouts (no. per min) 0.20 6 0.16 0.18 6 0.14 0.11 6 0.09 b 0.27 6 0.16 0.23 6 0.16 0.15 6 0.12 Total distance (m$min 21 ) 97.3 6 9.6 96.3 6 15.2 98.0 6 16.0 95.8 6 8.1 98.2 6 11.3 95.7 6 13.9 Low-speed distance (m$min 21 ) 89.7 6 9.3 90.2 6 14.4 90.9 6 15.2 88.9 6 7.7 90.9 6 10.1 88.9 6 13.7 High-speed distance (m$min 21 ) 7.9 6 1.0 b 6.1 6 1.9 7.1 6 1.3 6.9 6 2.2 7.3 6 1.6 6.7 6 1.9 *Data are mean 6 SD. RHIE = Repeated high-intensity effort. Denotes significant differences (p # 0.05) between high fitness and low fitness groups. Effect sizes of 0.50 0.79 and.0.80 were considered moderate (superscripted a) and large (superscripted b), respectively. www.nsca.com

Fitness and Match Performance in Elite Rugby League TABLE 2. Relationship between tests of physical qualities and absolute measures of match performance.* RSA PHIIRA VȮ 2 max Match time CollTot RHIE DistTot LowSp HighSp RSA 1.00 PHIIRA 20.39 1.00 VȮ 2 max 20.30 0.29 1.00 Match time 0.15 0.41 20.29 1.00 CollTot 0.33 20.51z 0.24 20.12 1.00 RHIE 0.04 20.26 0.21 20.10 0.60z 1.00 DistTot 0.15 0.42z 20.23 0.93z 20.17 20.17 1.00 LowSp 0.15 0.41 20.23 0.93z 20.18 20.17 0.99z 1.00 HighSp 0.16 0.48z 20.19 0.87z 20.08 20.12 0.84z 0.82z 1.00 *RSA = repeated-sprint ability; PHIIRA = prolonged, high-intensity intermittent running ability; VȮ 2 max = predicted maximal aerobic power; Match Time = total number of minutes played during matches; CollTot = total number of collisions; RHIE = repeated highintensity effort bouts; DistTot = total distance covered; LowSp = low-speed activity; HighSp = high-speed running. Denotes significance at p # 0.05. zdenotes significance at p # 0.01. Global Positioning System Analysis Global positioning system (GPS) data were collected during 16 elite rugby league matches. Movement was recorded by a minimaxx GPS unit (Team 2.5; Catapult Innovations, Melbourne, Australia) sampling at 5 Hz. The GPS signal provided information on speed, distance, position, and acceleration. The GPS unit also included triaxial accelerometers and gyroscopes sampling at 100 Hz, to provide information on physical collisions and repeated high-intensity efforts. The unit was worn in a small vest, on upper back of players. Data were categorized into (a) movement speed bands, corresponding to low (0 5 m$s 21 ) and high (.5 m$s 21 ) speeds (14); (b) sprinting (.7 m$s 21 ); (c) collisions (11); and (d) repeated high-intensity effort bouts (8,14). A repeated high-intensity effort bout was defined as $3 maximal ($2.79 m$s 22 ) acceleration, high speed, or contact efforts with,21 seconds recovery between efforts (8,14). The minimaxx units have been shown to have acceptable validity and reliability (15,20). In addition, minimaxx units have been shown to offer a valid measurement of tackles and repeated efforts commonly observed in collision sports (11). Statistical Analyses Players were separated into high fitness and low fitness groups based on ir results for repeated-sprint ability, prolonged high-intensity intermittent running ability, and TABLE 3. Relationship between tests of physical qualities and relative measures of match performance (per minute of match play).* RSA PHIIRA VȮ 2 max Match time CollTotMin RHIEMin DistTotMin LowSpMin HighSpMin RSA 1.00 PHIIRA 20.39 1.00 VȮ 2 max 20.30 0.29 1.00 Match time 0.15 0.41 20.29 1.00 CollTotMin 0.16 20.64z 0.27 20.65z 1.00 RHIEMin 20.03 20.39 0.30 20.51z 0.66z 1.00 DistTotMin 0.03 0.04 0.18 20.12 0.12 0.08 1.00 LowSpMin 0.04 20.01 0.15 20.13 0.13 0.08 0.99z 1.00 HighSpMin 20.06 0.40 0.26 0.01 20.01 0.04 0.40 0.27 1.00 *RSA = repeated-sprint ability; PHIIRA = prolonged, high-intensity intermittent running ability; VȮ 2 max = predicted maximal aerobic power; Match Time = total number of minutes played during match play; CollTotMin = total number of collisions performed per minute of match play; RHIEMin = repeated high-intensity effort bouts per minute of match play; DistTotMin = total distance covered per minute of match play; LowSpMin = low-speed activity per minute of match play; HighSpMin = high-speed running per minute of match play. Denotes significance at p # 0.05. zdenotes significance at p # 0.01. 1542

www.nsca.com predicted VȮ 2 max tests. Data were dichotomized according to median value. Differences in physical demands of match play between high fitness and low fitness groups were compared using statistical significance testing and by using a practical approach based on real-world relevance of results (1). First, differences in physical demands (i.e., distance covered at low and high speeds, collisions, and repeated high-intensity effort activity) between high fitness and low fitness groups were compared using an independent t-test. The level of significance was set at p # 0.05, and all data are reported as mean 6 SD. Second, given practical nature of study, differences in match demands of high fitness and low fitness groups were also analyzed using Cohen s effect size (ES) statistic (5). Effect sizes of,0.09, 0.10 0.49, 0.50 0.79, and.0.80 were considered trivial, small, moderate, and large, respectively (5). Partial correlations (controlling for effect of playing position) were also used to assess relationship between tests of physical qualities and physical match performance. RESULTS Physical Match Performance of Players With High and Low Fitness The physical qualities of players with high and low fitness are shown in Table 1. Players with well-developed repeated-sprint ability performed significantly (p # 0.05) more high-speed running (ES = 0.9) per minute of match play. No or differences were found between players with high and low repeated-sprint ability for physical match performance variables. Players with well-developed, prolonged, high-intensity intermittent running ability spent significantly (p # 0.05) more time on field (ES = 1.3), covered greater total distance (ES = 1.4), and more distance in low-speed (ES = 1.4) and high-speed running (ES = 1.0). Players with poor, prolonged, high-intensity intermittent running ability engaged in significantly (p # 0.05) more total collisions and repeated high-intensity effort bouts during match play. Players with well-developed predicted VȮ 2 max engaged in a greater number of total collisions (ES = 0.7) and total collisions per minute of match play (ES = 0.7). Association Between Physical Qualities and Physical Match Performance There were several relationships between tests of physical qualities and physical match performance variables (Tables 2 and 3). In general, tests of physical qualities were positively associated with match running variables; players with better, prolonged, high-intensity intermittent running ability covered greater total distance and greater distance in high-speed running during match play. Conversely, an inverse relationship was found between tests of physical qualities and both absolute and relative number of total collisions, and number of repeated high-intensity effort bouts. A strong association (r = 0.60 0.66, p # 0.01) was found between total number of collisions performed in match play and number of repeated high-intensity effort bouts. DISCUSSION This study is first to investigate relationship between tests of physical qualities and match performance in elite rugby league players and determine wher physical running qualities are associated with collision and repeated high-intensity effort performance in this sport. The results of this study demonstrate a significant relationship between tests of prolonged high-intensity running ability and distance covered in high-speed running during elite rugby league match play. However, inconsistent relationships were found between tests of running abilities and or match performance variables, with prolonged high-intensity running ability (negative), VȮ 2 max (positive), and repeatedsprint ability (no relationship) differentially associated with total number of collisions and repeated high-intensity effort bouts performed in competition. These findings demonstrate importance of prolonged high-intensity running ability to match running performance of elite rugby league players but also highlight need for game-specific conditioning to prepare players for high-intensity collision and repeated-effort demands of game. The amount of high-speed running performed in matches was significantly related to tests of prolonged high-intensity intermittent running ability in elite rugby league players of this study. Indeed, players with better, developed, prolonged, high-intensity intermittent running ability covered greater absolute and relative distances in high-speed running than players with relatively poorer, prolonged, highintensity intermittent running ability. Players with better, prolonged, high-intensity intermittent running ability also covered greater total distances across duration of match. These results are consistent with findings from top-class elite, moderate elite, and young male soccer players; players with higher Yo-Yo intermittent recovery test performances covered greater distances in high-speed running during matches (3,17,19). Although Yo-Yo intermittent recovery test is not strictly comparable to prolonged, high-intensity intermittent running ability test used in this study, it is still a test of repetitive high-intensity running ability. These findings emphasize importance of prolonged, high-intensity intermittent running ability to high-intensity running performance in elite rugby league match play. However, although measures of prolonged high-intensity intermittent running ability were positively associated with match running performance, an inverse relationship was found between this quality and number of collisions and repeated high-intensity effort bouts performed in matches. From a practical perspective, se findings highlight distinction between running and repeatedeffort physical qualities; well-developed, prolonged, highintensity intermittent running ability appears to prepare VOLUME 27 NUMBER 6 JUNE 2013 1543

Fitness and Match Performance in Elite Rugby League players for running demands of competition but does not necessarily prepare players for repeated high-intensity effort and collision demands of match play. This study failed to find a significant relationship between repeated-sprint ability and high-speed running distance, although players with better developed repeated-sprint ability performed more high-speed running per minute of match play than players with poorly developed repeatedsprint ability. This finding is in partial agreement with ors (21) who have found a strong relationship between repeated-sprint ability and amount of very high speed running and sprinting distance performed in soccer. The lack of association between repeated-sprint ability and physical match performance in this study may be explained by relative homogeneity of our cohort; a large spread of physical qualities within sample is likely to improve probability of finding a significant relationship between variables. We have recently shown that repeated high-intensity effort bouts (involving sprinting and tackling, with short recovery) are far more common than repeated-sprint bouts (involving sprinting in isolation, with short recovery) during elite rugby league match play (8). Moreover, heart rate, perceived exertion, and fatigue associated with repeated high-intensity effort activity are significantly greater than that associated with repeated-sprint activity (16). The lack of significant relationship between our test of repeated-sprint ability and repeated high-intensity effort performance in matches, coupled with findings of ors (8,16), suggest that repeated-sprint ability and repeated high-intensity effort ability are two distinct and different qualities. As such, training that only includes repeated-sprinting may result in players being underprepared for repeated high-intensity effort demands of elite rugby league match play (14). We found a lack of association between predicted VȮ 2 max and running match performance variables. However, significant positive relationships were found between predicted VȮ 2 max and both number of collisions and repeated high-intensity effort bouts performed during match play. Although we are circumspect in our interpretation of se associations, recent evidence has shown that aerobic qualities (in form of maximal aerobic speed) may contribute to repeated-effort performance (2). Presumably, well-developed aerobic qualities stimulate physiological adaptations that facilitate recovery between repeated accelerations and high-intensity collisions. Interestingly, players with higher predicted VȮ 2 max played significantly shorter match time than players with lower predicted VȮ 2 max. Although se results are difficult to reconcile, it is likely that players with greater aerobic fitness were required to be interchanged more frequently, as a consequence of fatigue associated with performing more collisions and repeated high-intensity effort bouts. This study found a strong relationship between number of repeated high-intensity effort bouts and total collisions performed during rugby league match play, with 36 44% of variance in repeated high-intensity effort performance explained by total number of collisions performed. These findings suggest that repeated high-intensity effort bouts consist predominantly of collisions. Furrmore, se results highlight clear distinction between soccer (a high-intensity running sport) and rugby league (a high-intensity collision sport) and provide furr explanation for lack of association between our test of repeated-sprint ability and repeated high-intensity effort performance. Although present results suggest that game-specific contact conditioning may be required to prepare players for repeated high-intensity effort demands of rugby league match play, it should also be recognized that not all conditioning needs to be game specific. Indeed, some general conditioning (e.g., maximal aerobic speed training) and strength training will promote aerobic, neural, skeletal, and tissue adaptations that allow players to perform skills of rugby league (7). In addition, given that repeated highintensity effort activity is also highly fatiguing (11), excessive volumes of this form of conditioning could lead to adverse training adaptations (injury, illness, fatigue, and overtraining) (9). For example, it has recently been shown that large volumes of high-intensity activity contribute to risk of soft tissue injury in elite team sport athletes (10). With se results in mind, clearly high-intensity conditioning components require appropriate planning and scheduling within training program and should be performed in combination with appropriate recovery activities to avoid neuromuscular and psychological fatigue, illness, overtraining, and injury (6,9). Furrmore, given fatigue associated with competition and recovery required between matches, greatest adaptations in repeated high-intensity effort ability are likely to occur in preseason training period. In conclusion, results of this study demonstrate a significant relationship between tests of prolonged high-intensity running ability and distance covered in high-speed running during elite rugby league match play. However, inconsistent relationships were found between tests of running abilities and or match performance variables, with prolonged highintensity running ability (negative), VȮ 2 max (positive), and repeated-sprint ability (no relationship) differentially associated with total number of collisions and repeated high-intensity effort bouts performed in competition. These findings demonstrate importance of prolonged high-intensity running ability to match running performance of elite rugby league players but also highlight need for game-specific conditioning to prepare players for high-intensity collision and repeated-effort demands of game. PRACTICAL APPLICATIONS The positive relationship between our test of prolonged, high-intensity intermittent running ability and high-speed running in elite rugby league matches demonstrates need 1544

www.nsca.com to adequately prepare players for running demands of competition. In addition, although well-developed, prolonged, highintensity intermittent running ability was associated with greater total distance and greater distance covered in highspeed running, an inverse relationship was found between this physical quality and number of collisions and repeated high-intensity effort bouts in which players engaged during competition. These findings highlight need for game-simulated contact conditioning of players to adequately prepare m for repeated high-intensity effort nature of rugby league. Based on previous findings (14), se repeated high-intensity effort bouts should include a minimum of 6 efforts, each of at least 6 seconds duration, using a work:rest ratio of 1:1. Finally, we found a lack of association between repeatedsprint ability and repeated high-intensity effort performance in matches. These findings suggests that repeated-sprint and repeated high-intensity effort ability are two distinct and different qualities and demonstrate need for a test of repeated high-intensity effort ability for collision sport athletes to assess ir preparedness for competition. REFERENCES 1. Batterham, AM and Hopkins, WG. Making meaningful inferences about magnitudes. Int J Sports Physiol Perform 1: 50 57, 2006. 2. Buchheit, M. Repeated-sprint performance in team sport players: Associations with measures of aerobic fitness, metabolic control and locomotor function. Int J Sports Med 33: 230 239, 2012. 3. Castagna, C, Impellizzeri, F, Cecchini, E, Rampinini, E, and Alvarez, JC. Effects of intermittent-endurance fitness on match performance in young male soccer players. J Strength Cond Res 23: 1954 1959, 2009. 4. Castagna, C, Manzi, V, Impellizzeri, F, Weston, M, and Barbero Alvarez, JC. Relationship between endurance field tests and match performance in young soccer players. J Strength Cond Res 24: 3227 3333, 2010. 5. Cohen, J. Statistical Power Analysis for Behavioural Sciences (2nd ed.). New York, NY: Academic Press, 1988. 6. Gabbett, TJ. Influence of training and match intensity on injuries in rugby league. J Sports Sci 22: 409 417, 2004. 7. Gabbett, TJ. Influence of fatigue on tackling technique in rugby league players. J Strength Cond Res 22: 625 632, 2008. 8. Gabbett, TJ. Sprinting patterns of National Rugby League competition. J Strength Cond Res 26: 121 130, 2012. 9. Gabbett, TJ and Jenkins, DG. Relationship between training load and injury in professional rugby league players. J Sci Med Sport 14: 204 209, 2011. 10. Gabbett, TJ and Ullah, S. Relationship between running loads and soft-tissue injury in elite team sport athletes. J Strength Cond Res 26: 953 960, 2012. 11. Gabbett, T, Jenkins, D, and Abernethy, B. Physical collisions and injury during professional rugby league skills training. J Sci Med Sport 13: 578 583, 2010. 12. Gabbett, TJ, Jenkins, DG, and Abernethy, B. Relationships between physiological, anthropometric, and skill qualities and playing performance in professional rugby league players. J Sports Sci 29: 1655 1664, 2011. 13. Gabbett, TJ, Jenkins, DG, and Abernethy, B. Relative importance of physiological, anthropometric, and skill qualities to team selection in professional rugby league. J Sports Sci 29: 1453 1461, 2011. 14. Gabbett, TJ, Jenkins, DG, and Abernethy, B. Physical demands of professional rugby league training and competition using microtechnology. J Sci Med Sport 15: 80 86, 2012. 15. Jennings,D,Cormack,S,Coutts,AJ,Boyd,L,andAughey,RJ.The validity and reliability of GPS units for measuring distance in team sport specific running patterns. Int J Sports Physiol Perform 5: 328 341, 2010. 16. Johnston, RD and Gabbett, TJ. Repeated-sprint and effort ability in rugby league players. J Strength Cond Res 25: 2789 2795, 2011. 17. Krustrup, P, Mohr, M, Amstrup, T, Rysgaard, T, Johansen, J, Steensberg, A, Pedersen, PK, and Bangsbo, J. The yo-yo intermittent recovery test: Physiological response, reliability, and validity. Med Sci Sports Exerc 35: 697 705, 2003. 18. Krustrup, P, Mohr, M, Ellingsgaard, H, and Bangsbo, J. Physical demands during an elite female soccer game: Importance of training status. Med Sci Sports Exerc 37: 1242 1248, 2005. 19. Mohr, M, Krustrup, P, and Bangsbo, J. Match performance of highstandard soccer players with special reference to development of fatigue. J Sports Sci 21: 519 528, 2003. 20. Peterson, C, Pyne, D, Portus, M, and Dawson, B. Validity and reliability of GPS units to monitor cricket-specific movement patterns. Int J Sports Physiol Perform 4: 381 393, 2009. 21. Rampinini, E, Bishop, D, Marcora, SM, Bravo, DF, Sassi, R, and Impellizzeri, FM. Validity of simple field tests as indicators of matchrelated physical performance in top-level soccer players. Int J Sports Med 28: 228 235, 2007. 22. Ramsbottom, R, Brewer, J, and Williams, C. A progressive shuttle run test to estimate maximal oxygen uptake. Br J Sports Med 22: 141 144, 1988. 23. Weston, M, Castagna, C, Helsen, W, and Impellizzeri, F. Relationships among field-test measures and physical match performance in elite-standard soccer referees. J Sports Sci 27: 1177 1184, 2009. VOLUME 27 NUMBER 6 JUNE 2013 1545