Rugby league is a collision sport played in a number of countries worldwide. Two teams compete in 2 40-minute halves separated by a 10-minute rest period. Match play consists of frequent bouts of high-intensity activity (e.g., running, sprinting, and tackling) separated by short bouts of low-intensity activity (e.g., jogging, walking, and standing). The physiological demands are complex with the movement patterns and work-to-rest ratios varying significantly throughout a game (1,15,17,21,24). Players require high levels of speed, agility, aerobic and anaerobic power, and muscular strength and power to excel (16). Players are called upon to sprint multiple times during a game with sprinting comprising 50.1 ± 25 and 43.2 ± 18.9 seconds of match play in elite and semielite rugby league, respectively (21). Therefore, the ability to maintain sprint speed over the course of a game is thought to be vital for performance (5,10,18) and has been termed repeated-sprint ability (RSA ).
Unlike other team sports (e.g., soccer, basketball, and field hockey), the repeated high-intensity bouts experienced during a rugby league game often involve a physical collision or tackle (1,7,21). For this reason, repeated sprinting in isolation may not be representative of the high-intensity bouts of a rugby league game. The ability to perform repeated sprints with intermittent tackles can be termed repeated-effort ability (REA) and may better reflect the repeated high-intensity bouts experienced during rugby league training and competition. This notion is supported by the recent literature from the National Rugby League, which found that players were required to perform between 0 and 4 repeated-sprint bouts during competition (1,21). The repeated-effort demands appear more substantial with players being required to perform an average of 12 repeated-effort bouts per game (1). These data clearly show that RSA may not be as vital in rugby league as previously thought (5,10,18) and that REA may be more representative of the repeated high-intensity bouts of activity experienced during match play. The players who can maintain sprint performance while effecting tackles are more likely to deliver successful performances. For this reason, it is important to determine the impact of intermittent tackling on repeated-sprint performance.
Various physiological tests are used in team sports, and the ability of a test to be reliable is of great importance so that real changes in performance can be tracked over time (19). Although a number of studies have found repeated-sprint tests to offer good test–retest reliability (9,20,22,26), no study has documented the reliability of a repeated-effort test that incorporates tackling and physical contact.
The repeated-effort demands of rugby league match play appear to be substantial; therefore, assessing and training RSA may not represent or prepare players physically for the most demanding repeated high-intensity bouts experienced during competition. An understanding of the impact of intermittent tackling on repeated-sprint performance is clearly warranted. Assessing the relationship between RSA and REA is of great worth to determine whether RSA, and REA are 2 distinct qualities. In addition, it is important to determine whether REA can be reliably assessed. With this in mind, the purpose of this study was to (a) investigate the effect of tackling on repeated-sprint performance; (b) examine the relationship between RSA and REA; and (c) assess the reliability of the 2 tests.
Experimental Approach to the Problem
We hypothesized that (a) tackling would impair repeated-sprint performance and increase the physiological demands of repeated-sprint activity; (b) RSA and REA would be 2 distinct qualities; and (c) both RSA and REA could be reliability assessed in a field-based setting. To test these hypotheses, the study used a randomized, counterbalanced, crossover experimental design to investigate the influence of tackling on repeated-sprint performance in rugby league players. Players performed both a repeated-sprint test and a repeated-effort test on 2 separate occasions so that the influence of tackling on repeated-sprint performance could be determined. The test–retest reliability of each test was determined by each test being performed twice on separate occasions. Heart rate was recorded throughout each test to assess the physiological demands of both tests, whereas perceived effort was recorded for each player using a rating of perceived exertion (RPE) scale (4). This allowed the physiological cost of the added tackling to be determined. Finally, Pearson's product–moment correlation coefficients were used to determine the relationship between RSA and REA to assess whether the 2 tests were assessing distinct qualities.
Twelve rugby league players (age 22.7 ± 2.2 years; height 178.6 ± 9.6 cm; body mass 85.0 ± 10.7 kg) from the same club participated in this study. Data collection took place in the first month of the competitive season after a 2-month preseason period, with players free from injury, and in peak physical condition at the time of testing. Testing took place at the start of 2 consecutive training sessions, separated by 7 days. Before the testing sessions, all players underwent a habituation session to control for any learning effects. All players received a clear explanation of the study, including the risks and benefits of participation. Written informed consent was obtained from the players before participation in the study. All experimental procedures were approved by the Moray House School of Education (University of Edinburgh) ethical committee.
Players were required to refrain from exercise and caffeine consumption 24 hours before testing, and abstain from food for 2 hours before testing. Any player using creatine supplementation was excluded from the study. In addition, players were required to maintain a normal diet before testing and consume the same food 24 hours before each testing day. Players were randomly allocated to 2 groups, 1 group performing the repeated-sprint test on day 1 and the other performing the repeated-effort test before switching over a week later. Before each test, the players performed the same standardized dynamic warm-up, consisting of dynamic stretches and progressive running drills. The warm-up lasted approximately 10 minutes. After completion of the warm-up, players performed either the repeated-sprint or the repeated-effort tests.
The repeated-sprint protocol comprised 12 × 20-m sprints with each sprint commencing every 20 seconds (Figure 1A). This is specific to the distances covered and the work-to-rest ratios experienced in a game (1,15,21). This protocol also meets the criteria of a repeated-sprint bout outlined by Spencer et al. (23). Players were instructed to perform each sprint with maximal effort. Recovery was characterized by walking around a cone placed 10 m from the end of the sprint track, before walking back to the start line to perform the next sprint once 20 seconds had elapsed. Ten minutes after the cessation of the test, players then manned the tackle bags for the players performing the repeated-effort test.
The repeated-effort protocol comprised 12 × 20-m sprints and tackles with each sprint commencing every 20 seconds and the tackle performed after each 20-m sprint (Figure 1B). Players were instructed to perform each sprint with maximal effort. The tackle during the prescribed recovery period lasted approximately 4 seconds and involved accelerating forward 2 m before effecting a tackle on a player holding a standard hand-held tackle shield (measuring 87.5 × 40 cm2; Centurion Rugby, Dewsbury, United Kingdom) and grappling with the player for 3 seconds. The player holding the tackle shield was not brought to ground during the tackle and grapple. Both the tackler and the tackle shield holder were instructed to exert maximal force during the hit and grapple phases of the tackle, to mirror the contact demands of a game as accurately as possible.
Sprint performance was measured using 2 Canon MD101 video cameras (Canon UK, Surrey, United Kingdom) placed in elevated positions on the 10-m (start and finish) and the 30-m (start/finish) lines. The cameras panned across each sprint, recording when the player started, and when they crossed the finish line. Sprint time was assessed by taking the time from the first foot movement to when the player's chest crossed the finish line. Repeated-sprint ability and REA were assessed using the time of each individual sprint, total time (summation of all the sprints), and percentage decrement which was calculated using the following formula:
Ideal time was calculated using the following formula:
Ideal time = fastest sprint × number of sprints.
Physiological Responses and Perceived Exertion
Heart rate was recorded to determine the physiological responses to the tests. Heart rate was recorded using Polar Team heart rate monitors with the data subsequently downloaded to a computer for analysis using Polar Precision Performance software (Polar, Oulu, Finland). Players wore the heart rate belts for 2 minutes before commencing the test and 5 minutes after the cessation of the test. Average and peak heart rates were reported for the 2 tests; average heart rate was the mean heart rate taken from the start of the test to immediately at the end of each test. Borg's scale of RPE was required from each player immediately after the completion of each test as a measure of exertion (4).
Differences in the individual sprints, total time, percentage decrement, average heart rate, peak heart rate, and RPE between the 2 tests were compared using traditional significance testing and using more practical statistical tests based on the real-world relevance of the findings (3,14). Analyses were administered using the Statistical Package for Social Sciences SPSS 17.0 (SPSS Inc, Chicago, IL, USA). Differences between each sprint for both the repeated-sprint and repeated-effort tests were assessed using a 2-way repeated measures analysis of variance. Differences in total time, percentage decrement, heart rate, and RPE were assessed using paired samples t-tests. The significance level was set at p ≤ 0.05, and all data are reported as mean ± SD. Given the practical nature of the study and the relatively small sample size, Cohen's effect size (ES) statistic was used to determine the practical significance of any observed differences (6). Effect sizes of 0.2, 0.5, and 0.8 were considered small, moderate, and large, respectively (3,14). The Pearson product–moment correlation coefficient was used to determine the relationship between RSA and REA. Intraclass correlation coefficients and typical error of measurement (TE) were calculated to determine the test–retest reliability of the repeated-sprint and repeated-effort tests (12). Based on an alpha level of 0.05 and a sample size of 24 (12 players in each of the repeated-effort and repeated-sprint tests), our type 1 and 2 error rates were 0.5 and 25%, respectively, for detecting between-group ESs of 5% in total repeated-sprint time (13).
Repeated-Sprint Performance, Heart Rate, and Perceived Exertion
The data for repeated-sprint performance, heart rate, and perceived exertion for both tests are displayed in Table 1. There was a significantly greater (p ≤ 0.05) total time (ES = 1.19), average heart rate (ES = 1.64), peak heart rate (ES = 1.35), and RPE (ES = 3.39) in the repeated-effort test in comparison to the repeated-sprint test, with large ESs observed between tests (Table 1). A large difference (ES = 1.02, p = 0.06) was found for percentage decrement between the 2 tests. Figure 2 illustrates the differences in each individual sprint for both repeated-sprint and repeated-effort tests. There was a significant increase (p ≤ 0.05) in sprint time for sprints 8–12 compared to sprint 1 in the repeated-effort test, and sprints 4, 6, and 12 for the repeated-effort test were significantly slower (p ≤ 0.05) compared with sprints 4, 6, and 12 for the repeated-sprint test.
Relationship between Repeated-Sprint and Repeated-Effort Performance
No significant relationships (p > 0.05) were found between the repeated-sprint and repeated-effort tests (Table 2) for total time (r = 0.30), percentage decrement (r = −0.68), average heart rate (r = 0.32), peak heart rate (r = 0.46), and RPE (r = 0.03).
The test–retest reliability for the repeated-sprint and repeated-effort tests is shown in Table 3. Total time was more reliable than percentage decrement for both the repeated-sprint and repeated-effort tests. The repeated-effort test was shown to be more reliable than the repeated-sprint test for percentage decrement, average heart rate, and RPE, with reliability of peak heart rate measures being almost identical between the 2 tests.
The purpose of this study was to (a) investigate the influence of tackling on repeated-sprint performance, (b) determine whether repeated-sprint and REA are 2 distinct qualities, and (c) determine whether REA can be reliably measured in rugby league players. The findings of this investigation support our hypotheses and demonstrate that tackling has a significant physiological and functional cost when performed intermittently with repeated-sprints, with a significantly greater total time, average and peak heart rate, and perceived effort for the repeated-effort test compared with the repeated-sprint test. In addition, under the conditions of this study, RSA and REA appear to be 2 distinct qualities that can be reliably assessed in a field-based setting in rugby league players.
It is clear from the findings of this study that tackling has a great physiological and functional cost when performed intermittently with repeated sprints, with significantly greater average heart rate, peak heart rate, total time, and RPE for the repeated-effort test compared with the repeated-sprint test (Table 1). Furthermore, there was no significant increase in sprint time for the repeated-sprint test across the 12 sprints (Figure 2); however, sprints 8–12 were significantly slower than sprint 1 in the repeated-effort test; sprints 4, 6, and 12 in the repeated-effort test were also significantly slower than the corresponding sprints in the repeated-sprint test. These data are in agreement with others (8,11) highlighting the high physiological and functional cost of tacking when performed in conjunction with repeated-sprints (i.e., repeated-effort). These data suggest that exclusively performing repeated-sprints in preparation for the high-intensity repeated-effort demands of match play may leave players physically underprepared for the most demanding passages of play. In addition, using repeated-effort tests to assess players' ability to perform repeated high-intensity efforts may be a more specific measure of performance as opposed to repeated-sprint tests.
Pearson's correlation coefficients showed a nonsignificant relationship between the repeated-sprint and repeated-effort tests for total time (r = 0.30), percentage decrement (r = −0.68), average heart rate (r = 0.32), peak heart rate (r = 0.46), and RPE (r = 0.03) (Table 2), suggesting that the 2 protocols used assess 2 distinct and separate qualities (RSA and REA). This may be predictive of the different energy demands employed in the 2 tests. The work-to-rest ratio was much lower in the repeated-effort test (∼1:2) compared with the repeated-sprint test (∼1:6), which is likely to significantly affect bioenergetics for each test (2). The longer recovery period during the repeated-sprint test would have allowed greater phosphocreatine resynthesis (25) and may explain the smaller decrement in sprint performance in the repeated-sprint test. Based on the definition of a repeated-sprint bout (23), a repeated-effort bout has been defined as 3 or more sprints or tackles with <21 seconds between each effort (1). Because of tackling occurring in conjunction with sprint activity, repeated-effort bouts will place greater demands on anaerobic glycolysis; hence, the protocols are assessing 2 distinct qualities required of players. Because of the importance of REA during match play, with players being required to perform an average of 12 repeated-effort bouts per game (1), REA should be emphasized in training.
This study found that both RSA and REA can be reliably assessed in rugby league players (Table 3). Previous data indicate that RSA can be reliably tested (9,20,22,26), but no existing research has determined the reliability of assessing REA in rugby league. Total time was the most reliable measure of RSA and REA as opposed to percentage decrement, which was a less reliable measure of RSA (TE = 22.5%) and REA (TE = 6.7%). These data are in accordance with previous research (9,20,22) and further support the notion that total time is the most reliable method of assessing repeated-sprint and repeated-effort performance.
The repeated-effort test proved more reliable than the repeated-sprint test (Table 3) for percentage decrement (TE, 6.7 vs. 22.5%), average heart rate (TE, 1.5 vs. 3.5%), and RPE (TE, 3.3 vs. 5.5%), with peak heart rate being almost identical between the 2 tests (TE, 1.5 vs. 1.4%). The repeated-sprint test showed greater reliability for total time (TE, 1.5%) compared with the repeated-effort test (TE, 2.3%). Greater reliability in the repeated-effort test may be explained by the sample investigated. Rugby league players perform repeated-effort activity more regularly than repeated-sprint activity (1), so they may be able to perform repeated-effort exercise more consistently compared with other team sport athletes. Despite the added contact in the repeated-effort test, REA can still be reliably tested in rugby league players when the players give maximal effort, and contact is closely controlled.
The selection of variables for the 2 tests was based on both scientific literature and consultation with support staff from elite rugby league. The sprint distance (20 m) is representative of the sprint distances experienced during match play (1,15,21). The tackling (hit and 3-second grapple) is similar to contact experienced during match play although it was performed in a more controlled fashion. The sprint number and tackle number (12) induced a moderate amount of fatigue to distinguish players of different RSA and REA and met the criteria for a repeated-sprint and repeated-effort bout (1,23). The type of recovery (both active and passive locomotion) is an accurate representation of recovery experienced during match play (15,17,21). The mode of exercise (running) is the same as that experienced during games. For this reason, and the inherent reliability of the tests, these protocols could be considered useful in assessing RSA and REA in rugby league players. Determining the external validity of these tests in discriminating players of different repeated-sprint and REA at higher levels of play (e.g., semielite and elite) is also required.
In conclusion, this study demonstrates that tackling performed in conjunction with repeated sprints (i.e., repeated-effort exercise) has a significant physiological and functional cost when compared with repeated-sprinting alone. In addition, this study found that RSA and REA are 2 distinct and separate qualities that can both be reliably assessed in rugby league players.
There are a number of practical applications from this study that are relevant to the strength and conditioning coach. Based on the evidence from this study, repeated-sprint and RSA and REA are 2 distinct qualities required of rugby league players. Consequently, distinct tests and training methods addressing these 2 distinct qualities should be considered by sport scientists and coaches.
Exclusively training RSA in collision sports may leave players underprepared for the most demanding passages of play. As such, performing repeated high-intensity efforts during training that reflect the most demanding passages of play appears vital in preparing players for competition.
The RSA and REA are physical qualities that can be reliably assessed in rugby league players. Repeated-effort tests may be superior in assessing a player's readiness to cope with the most severe repeated high-intensity efforts experienced during match play as opposed to repeated-sprint tests.
Total sprint time is the best method for tracking changes in RSA and REA over time. Despite this, calculating both total sprint time and percentage decrement may provide the practitioner with greater utility when assessing repeated-sprint and REA within a group of players.
The authors would like to thank the players for giving up their time to participate in the study.
1. Austin, D, Gabbett, TJ, and Jenkins, D. Repeated-high intensity exercise in professional rugby league. J Strength Cond Res
, in press.
2. Balsom, P, Seger, J, and Sjodin, B. Maximal-intensity intermittent
exercise: Effect of recovery duration. Int J Sports Med
13: 528–533, 1992.
3. Batterham, AM and Hopkins, WG. Making meaningful inferences about magnitudes. Int J Sports Physiol Perform
1: 50–57, 2005.
4. Borg, GA. The psychophysical basis of perceived exertion. Med Sci Sports Exerc
14: 377–381, 1982.
5. Clark, L. A comparison of the speed characteristics of elite rugby league players by grade and position. Strength Cond Coach
10: 2–12, 2003.
6. Cohen, J. Statistical Power Analysis for the Behavioral Sciences
. (2nd ed.). Hillsdale, NJ: Lawrence Erlbaum, 1998.
7. 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.
8. Gabbett, TJ. Influence of fatigue on tackling
technique in rugby league players. J Strength Cond Res
22: 625–632, 2008.
9. Gabbett, TJ. The development of a test of repeated-sprint ability for elite women's soccer players. J Strength Cond Res
24: 1191–1194, 2010.
10. Gabbett, TJ, King, T, and Jenkins. Applied physiology of rugby league. Sports Med
38: 119–138, 2008.
11. Gissane, C, White, J, Kerr, K, and Jennings, D. Physical collisions in professional super league: The demands of different player positions. Cleve Med J
4: 137–146, 2001.
12. Hopkins, WG. Measures of reliability in sports medicine and science. Sports Med
30: 1–15, 2000.
13. Hopkins, WG. Estimating sample size for magnitude-based inferences. Sportscience
(serial online) 10: 63–70, 2006. Available at: sportsci.org/2006/wghss.htm. Accessed August 10, 2010.
14. Hopkins, WG. Probabilities of clinical or practical significance. Sportscience
(serial online) 6, 2002. Available at: sportsci.org/jour/0201/wghprob.htm. Accessed August 10, 2010.
15. King, T, Jenkins, D, and Gabbett, T. A time–motion analysis of professional rugby league match-play. J Sports Sci
27: 213–219, 2009.
16. Meir, R. A model for the integration of macrocycle and microcycle structure in professional rugby league. Strength Cond Coach
2: 6–12, 1994.
17. Meir, R, Colla, P, and Milligan, C. Impact of the 10-meter rule change on professional rugby league: Implications for training. Strength Cond J
23: 42–46, 2001.
18. O'Connor, D. Physiological characteristics of professional rugby league players. Strength Cond Coch
4: 21–26, 1996.
19. Pyne, DB. Interpreting the results of fitness testing. In: Gastrolyte VIS International Science and Football Symposium, Victorian Institute of Sport, Melbourne, Australia,
20. Pyne, DB, Saunder, PU, Montgomery, PG, Hewitt, AJ, and Sheehan, KP. Relationships between repeated-sprint testing, speed, and endurance. J Strength Cond Res
22: 1633–1637, 2008.
21. Sirotic, AC, Coutts, AJ, Knowles, H, and Catterick, C. A comparison of match demands between elite and semi-elite rugby league competition. J Sports Sci
27: 1–9, 2009.
22. Spencer, M, Fitzsimons, M, Dawson, B, Bishop, D, and Goodman, C. Reliability of a repeated-sprint test for hockey. J Sci Med Sport
9: 181–184, 2006.
23. Spencer, M, Lawrence, S, Rechichi, C, Bishop, D, Dawson, B, and Goodman, C. Time–motion analysis of elite field hockey, with special reference to repeated-sprint activity. J Sports Sci
22: 843–850, 2004.
24. Sykes, D, Twist, C, Hall, S, and Nicholas, C. Semi-automated time–motion analysis of senior elite rugby league. Int J Perform Anal Sport
9: 47–59, 2009.
25. Walter, G, Vandenborne, K, McCully, KK, and Leigh, JS. Noninvasive measurement of phosphocreatine recovery kinetics in single human muscles. Am J Physiol
272: C525–C534, 1997.
26. Wragg, CB, Maxwell, NS, and Doust, JH. Evaluation of the reliability and validity of a soccer-specific field test of repeated sprint ability. Eur J Appl Physiol
83: 77–83, 2000.
Keywords:© 2011 National Strength and Conditioning Association
collision sport; physiological demands; intermittent; tackling