Secondary Logo

Journal Logo

Original Research

Muscular Strength and Power Correlates of Tackling Ability in Semiprofessional Rugby League Players

Speranza, Michael J.A.1; Gabbett, Tim J.1,2; Johnston, Rich D.1; Sheppard, Jeremy M.3

Author Information
Journal of Strength and Conditioning Research: August 2015 - Volume 29 - Issue 8 - p 2071-2078
doi: 10.1519/JSC.0000000000000897
  • Free

Abstract

Introduction

Rugby league is a collision sport played internationally at junior and senior levels. The game is intermittent in nature, characterized by bouts of high-intensity running, collisions, and tackling, separated by periods of lower-intensity activity (25,34). The skill set required for rugby league is multifaceted with players requiring good ball handling ability (e.g., catching, passing, and kicking), quick and accurate decision making, and the ability to perform effective tackles (20). Rugby league players require well-developed aerobic fitness, speed, muscular strength and power, and agility to compete at an elite level (28). An understanding of how these physical qualities relate to specific rugby league skills is essential for the production of specific coaching, and strength and conditioning programs.

Rugby league players are subjected to multiple physical collisions throughout a match, most of which occur while players are defending (19,32). In defense, players are required to make contact and tackle opposition players to halt their forward progress. The number of tackles that players are required to make is dependent on playing position (22). Generally, forwards will perform an average of 39 tackles compared with the backs who perform an average of 16 tackles per match (22). A large part of success in a collision sport such as rugby league is based on tackling ability, the capacity to dominate the tackle contest, and the ability to tolerate physical impacts (8). Tackling technique as examined by a one-on-one tackling drill has been found to be strongly associated with the proportion of missed tackles (negative) and the proportion of dominant tackles (positive) that players complete during match-play (10). Therefore, the ability to perform a well-executed tackle is critical for the player to “win” the contact contest.

The majority of rugby league injuries occur during physical collisions and tackles (13,14). Studies have shown that up to 77.2% of all injuries occur during tackles, with 40% of these injuries occurring to the player performing the tackle (13–15,29). It has been proposed that poor tackling technique may be a significant risk factor for injury (23,30); however, there is limited evidence to support this claim (21). In the interest of injury prevention, authors have suggested that improving tackling technique may decrease the likelihood of injury while making a tackle (11,31).

Several studies have examined the physiologic and anthropometric correlates of tackling ability in subelite and professional rugby league players (16–18). Well-developed acceleration (over a 10-meter sprint) and lower-body muscular power are associated with superior tackling ability in elite junior and professional rugby league players (16–18). These studies have provided great insight into the physiological factors that impact on tackling ability; however, there are some gaps in current research. Although maximal muscular strength and power have been shown to discriminate between elite and subelite rugby league players (1,4), and muscular strength and power are associated with acceleration (2,7,27), to date, no study has examined the influence of upper-limb and lower-limb muscular strength on tackling performance. Furthermore, no study has examined the physiological correlates of tackling ability in semiprofessional rugby league players. With this in mind, the purpose of this study was to examine the tackling ability of semiprofessional rugby league players and investigate the relationship between muscular strength and power qualities, and tackling ability in these players.

Methods

Experimental Approach to the Problem

To test our hypothesis, a cross-sectional experimental design was used to compare muscular strength and power qualities, and tackling ability in first grade, second grade, and under 20s players. Pearson's product-moment correlation coefficients were used to determine the relationship between the independent variables (i.e., muscular strength and power), and the dependant variable (i.e., tackling ability). It was hypothesized that players with superior upper-body and lower-body muscular strength and power would have more effective tackling technique.

Subjects

Thirty-six rugby league players (mean ± SD age, 23.1 ± 3.6 years) participated in this study. All players were from 1 of the 3 teams in the same rugby league club; first grade players (n = 10) competed in a state level competition, second grade players (n = 12) competed in a metropolitan competition, and under 20s players (n = 14) who were younger than 20 years competed in a metropolitan competition. Players were classified as semiprofessional because they not only received remuneration for playing rugby league but also relied on other forms of income. Players were free from injury and midway through a 15-week preseason training program when they undertook muscular strength and power testing, and the tackling assessment. All players received a detailed explanation of the study including information on the risks and benefits. Written informed consent was obtained before the start of the study. The players were free to withdraw from the study at any time. All the procedures for this study were preapproved by the Australian Catholic University Ethics Reviewing Panel.

Muscular Strength

Upper-body and lower-body muscular strength was assessed using a 3 repetition maximum (3RM) bench press and squat test, respectively. The players were familiar with the tests because they were part of routine testing. The tests were conducted 72 hours after the previous session, and players were instructed to refrain from excessive exercise before the testing session. The testing occurred in the evening. Players were instructed to maintain their normal diet and hydration as they would for normal training sessions. For the 3RM test, the players were instructed to perform progressively heavier loads, with 3–5 minutes' rest between sets, until they attempted a load that they could lift for a maximum of 3 full range repetitions. A strength and conditioning specialist familiar with the players supervised and guided the players to perform the squats to below parallel. The intraclass correlation coefficients for test-retest reliability and typical error of measurement were 0.96 and 2.6% for the 3RM bench press and 0.91 and 3.6% for the 3RM squat, respectively. Relative upper-body and lower-body strength were calculated by dividing the 3RM of the bench press and squat by the player's body mass.

Muscular Power

Lower-body and upper-body peak power was assessed with the players performing a countermovement jump (CMJ) and plyometric push-up (PPU) on a force platform with a sampling rate of 500 Hz (Kistler 9290AD Force Platform; Winterthur, Switzerland). To perform the CMJ, players were required to keep their hands on their hips for the duration of the movement. When instructed, the players dipped to a self-selected depth before explosively jumping as high as possible. Players had 2 attempts with their highest power output recorded. The intraclass correlation coefficients for test-retest reliability and typical error of measurement for CMJ peak power were 0.81 and 3.5%, respectively. For the PPU, the players were instructed to place their hands on the force platform, whereas in the push-up position, with their arms at full extension. When indicated, the players lowered their body before performing an explosive push-up that caused their hands to leave the platform. The players had 2 attempts with their highest power output recorded. All testing occurred at the start of a regular training session to limit fatigue-related interference. The intraclass correlation coefficients for test-retest reliability and typical error of measurement for the PPU were 0.97 and 3.8%, respectively.

Tackling Technique

The protocol used to examine tackling ability through the video analysis of a standardized one-on-one defensive drill was the same used in previous studies (16–18). The drill was conducted in a 10-meter grid with video cameras (Canon Legria HV40, Japan) on the left, right, and rear of the drill. The drill required the participant to tackle a participant carrying a ball of similar height and mass. The ball carrying participant was required to run directly at the tackling participant and take no evasive action. The participants performed 6 consecutive tackles, 3 on the right shoulder, and 3 on the left shoulder. The drill was performed 48 hours after the strength and power testing and at the start of a training session so that the participants were not in a fatigue state. Tackling technique was assessed by a sport scientist using standardized technical criteria that have been used in previous studies of tackling technique in rugby league players (16–18).

The technical criteria included

  • Contact made at the center of gravity
  • Initial contact made with the shoulder
  • Body position square and aligned
  • Leg drive on contact
  • Watch the target onto the shoulder
  • Center of gravity forward of the base of support.

Each tackle received a score of 6 (arbitrary units). Players were awarded 1 point for each criterion they achieved or 0 points if they failed to meet the criteria while performing a tackle. The players received an aggregate score (arbitrary units) from all 6 tackles, which was then converted to a percentage. Movement velocity immediately before contact was calculated using video analysis (Silicon Coach, New Zealand). The intraclass correlation coefficient for test-retest reliability and typical error of measurement for tackling technique were 0.88 and 3.9%, respectively. The intraclass correlation coefficient for test-retest reliability and typical error of measurement for the movement velocity were 0.94 and 2.9%, respectively.

Statistical Analyses

Data were tested for normality using a Shapiro-Wilk test. Analysis of variance with post hoc testing (Tukey) was used to establish statistical differences in the muscular strength and power, and tackling ability among the different playing levels. Differences in physiologic variables and tackling ability between the 3 different playing levels were also compared using Cohen's effect size (ES) statistic (6). Effect sizes of <0.2, 0.2–0.6, 0.61–1.2, 1.21–2.0, and >2.0 were considered trivial, small, moderate, large, and very large, respectively (5). Pearson product-moment correlation coefficients were used to determine the relationships among muscular strength and power, and tackling ability. The level of significance was set at p ≤ 0.05.

Results

Strength and Power Qualities

The raw data (mean values ± SD), along with magnitudes of the differences between the muscular strength and power of the 3 playing groups, are presented in Table 1. Although no significant differences in muscular strength and power were found between the 3 playing levels, small-to-moderate differences were found between first grade and second grade players (p = 0.18; ES = 0.22) and first grade and under 20 players (p = 0.08; ES = 1.02) for upper-body strength. The first grade players demonstrated greater lower-body strength than the second grade (p = 0.51; ES = 0.49) and under 20s players (p = 0.72; ES = 0.31); there was a trivial difference between the under 20s and second grade teams (p = 0.92; ES = −0.16). First grade players had better bench press relative to their body mass than second grade (p = 0.73; ES 0.32) and under 20s (p = 0.37; ES = 0.80) players; there was a small difference between second grade and under 20s players (p = 0.82; ES = 0.20). A trivial difference was found between the first grade and the under 20s players (p = 0.98; ES = 0.03) for relative squat; however, a small difference was found for both grades when compared with the second grade team. Trivial to small differences were found among playing groups for CMJ and PPU.

T1-1
Table 1:
Tackling ability and muscular strength and power characteristics of semiprofessional rugby league players.*†

Tackling Ability

Tackling ability and velocity before contact of the 3 playing groups are shown in Table 1. The first grade players had superior (although nonsignificant) tackling ability compared with the second grade (p = 0.50; ES = 0.80) and under 20s (p = 0.06; ES = 1.02) players. There was also a small difference in tackling ability between second grade and under 20s (p = 0.42; ES = 0.55) players. The first and second grade players produced greater velocity at the point of contact than the under 20s players with the magnitudes of difference being small (p = 0.25; ES = 0.58) and moderate (p = 0.24; ES = 1.07), respectively. The average velocity before contact was higher in second grade players than in first grade players with a small difference (p = 0.26; ES = −0.22) found.

Relationship Between Strength and Power Qualities and Tackling Ability

Tables 2–5 outline the relationships between strength and power qualities, and tackling ability. Among all the players, the strongest correlates of tackling ability were 3RM squat (r = 0.67, p < 0.01), 3RM bench press (r = 0.58, p < 0.01), relative squat (r = 0.41, p = 0.01), and PPU (r = 0.56, p < 0.01). The strongest correlates of tackling ability in first grade players were 3RM squat (r = 0.72, p = 0.02), 3RM bench press (r = 0.72, p = 0.02), relative squat (r = 0.86, p < 0.01), and PPU (r = 0.70, p = 0.03). For second grade players, only relative squat (r = 0.60, p = 0.04) and PPU (r = 0.67, p = 0.02) were associated with tackling ability. The strongest correlates of tackling ability in under 20s players were 3RM squat (r = 0.77, p < 0.01), 3RM bench press (r = 0.70, p < 0.01), and PPU (r = 0.65, p = 0.01).

T2-1
Table 2:
Relationship among physiological characteristics and tackling ability in semiprofessional rugby league players.*†
T3-1
Table 3:
Relationship among physiologic characteristics and tackling ability in first grade semiprofessional rugby league players.*†
T4-1
Table 4:
Relationship among physiological characteristics and tackling ability in second grade semiprofessional rugby league players.*†
T5-1
Table 5:
Relationship among physiological characteristics and tackling ability in under 20s semiprofessional rugby league players.*†

Discussion

This study is the first to examine the strength and power correlates of tackling in semiprofessional rugby league players. It is also the first study to investigate the relationship between muscular strength qualities and rugby league tackling ability. The results from this study demonstrate that players competing at a higher competitive standard have superior tackling ability and, in general, the strongest correlates of tackling ability were maximal squat, maximal bench press, relative squat, and PPU. These findings demonstrate that well-developed muscular strength and upper-body power contribute to tackling ability in semiprofessional rugby league players.

As expected, the first grade squad demonstrated superior tackling technique when compared with the second grade team, who in turn had superior tackling ability to the under 20s players. The results of this study are consistent with other studies, which have shown that tackling ability can discriminate rugby league players of different playing levels (10,17,18). Two previous studies found moderate-to-large differences (ES = 1.10–1.53) in tackling ability between professional and semiprofessional players (10,18). Similarly, a study examining junior rugby league players found that elite players had greater tackling ability (ES = 0.82) than their subelite counterparts (17). The combined results of these studies suggest that tackling ability improves as the competitive standard increases.

This is the first study to examine the relationship between maximal strength and tackling ability. As hypothesized, lower-body and upper-body strength were shown to be closely associated with tackling ability in semiprofessional rugby league players. The strongest muscular strength correlates of tackling ability in the first grade squad were squat, bench press, and relative squat. Maximal squat and bench press were also associated with tackling ability in the under 20s squad; however, relative squat was not significantly related to tackling ability. The only strength quality that was significantly related to tackling ability in the second grade team was relative squat. A possible explanation for the lack of association between maximal squat and bench press, and tackling ability in the second grade players may be due to the standard of these players. Gabbett (12) concluded that at lower playing levels, physiologic capacities of players did not influence their selection or nonselection, suggesting that, at an amateur or subelite level, team selection was based more on body mass, playing experience, and skill. Despite this, these results highlight the significance of muscular strength qualities for effective tackling technique in rugby league.

The PPU was the only muscular power quality that was associated with tackling ability in all 3 grades, suggesting that upper-body power is significant to tackling ability impendent of playing standard. These results are in contrast to previous research. Gabbett (16) examined correlates of tackling ability in subelite rugby league players and used an overhead medicine ball throw to determine upper-body power and found there was no significant relationship between upper-body power and tackling ability. This discrepancy may be due to the different movement patterns used in the 2 tests. An overhead throwing movement is not very common in rugby league and therefore may not be as specific as the PPU, which replicates fending and pushing opponents that are fundamental actions in rugby league (3). Furthermore, the reliability of an overhead medicine ball throw has been shown to be affected by the weight of the ball thrown and throwing technique (33). The PPU test on a force platform has been shown to be a reliable protocol for measuring upper-body strength in rugby league players (24).

This study found that lower-body power, as measured by the CMJ, was not significantly related to tackling ability. This finding is in agreement with a previous study that found vertical jump performance was not significantly associated with tackling ability in subelite rugby league players (9). However, it is in conflict with other studies that found a significant association between vertical jump performance and tackling ability in professional and elite junior rugby league players (17,18). A possible reason for the lack of relationship between CMJ and tackling ability may be due to the lack of movement specificity of the test for lower-body power. A large component of tackling ability is the ability to produce high levels of horizontal leg drive to halt the forward progress of the attacking player. Maulder and Cronin (26) found that horizontal jump tests have stronger relationships to sprint ability than vertical jump tests with the authors suggesting that their finding was due to the horizontal nature of sprinting, which is not assessed by vertical jumping. Future studies should examine the relationship between horizontal leg power and tackling ability.

The strongest correlates of tackling ability were squat (r = 0.67), bench press (r = 0.58), relative squat (r = 0.41), and PPU (r = 0.56). The coefficient of determination (r2) for these strength and power qualities ranged between 17 and 45%. Therefore, 55–83% of the variance in tackling ability is explained by factors in addition to, or other than muscular strength and power characteristics. Although this study provides an important step in explaining the influence that muscular strength and power has on tackling ability, it must be acknowledged that additional factors (e.g., technical factors, experience) may explain a greater proportion of this skill.

The standardized one-on-one tackling drill has been shown to be significantly related to the proportion of missed tackles (r = −0.74) and the proportion of dominant tackles (r = 0.78) in professional rugby league match-play (10). To date, no study has examined how the standardized one-on-one tackling drill is related to match performance at a semiprofessional level, providing scope for future research.

In conclusion, this is the first study to examine the relationship between physiologic qualities and tackling ability in semiprofessional rugby league players. It is also the first study to examine the influence that muscular strength and power has on tackling ability. These findings demonstrate that muscular strength and upper-body power contribute to tackling ability in semiprofessional rugby league players. Further research examining the relationship of muscular strength and power on tackling ability in other competitive levels such as professional and junior players is warranted. Although this study has identified a number of physiologic qualities associated with tackling ability, the results do not imply cause and effect. Future studies should examine the influence of training-induced improvements in muscular strength and power on tackling ability.

Practical Applications

This study highlights the need for players to improve tackling ability because they progress higher in competitive standards. This is of particular importance to rugby league coaches developing young players. The standardized one-on-one tackling drill is a reliable and useful tool to evaluate and develop tackling technique.

The findings of this study demonstrate that well-developed muscular strength and upper-body power contribute to tackling ability in semiprofessional rugby league players. Although a significant correlation does not suggest causation, it does provide valuable insight into the physiologic variables that effect tackling ability.

It can be assumed that as long as the technical aspects of tackling technique are adequately coached and practiced, then enhancements in muscular strength and power may serve as foundational components to underpin improvement in tackling ability. This is of particular importance to strength and conditioning specialists and rugby league coaches when evaluating and addressing deficiencies in player's tackling ability.

Acknowledgments

The authors thank all players and coaching staff who participated in this study.

References

1. Baker DG. Differences in strength and power among junior-high, college-aged and elite professional rugby league players. J Strength Cond Res 16: 581–585, 2002.
2. Baker DG, Nance S. The relation between running speed and measures of strength and power in professional rugby league players. J Strength Cond Res 13: 230–235, 1999.
3. Baker DG, Newton RU. Discriminative analyses of various upper body tests in professional rugby-league players. Int J Sports Physiol Perform 1: 347–360, 2006.
4. Baker DG, Newton RU. Comparison of lower body strength, power, acceleration, speed, agility, and sprint momentum to describe and compare playing rank among professional rugby league players. J Strength Cond Res 22: 153–158, 2008.
5. Batterham AM, Hopkins WG. Making meaniningful inferences about magnitudes. Int J Sports Physiol Perform 1: 50–57, 2006.
6. Cohen J. Statistical Power Analysis for the Behavioural Sciences (2nd ed.). Hillsdale, NJ: Lawrence Erlbaum, 1988.
7. Cronin JB, Hansen KT. Strength and power predictors of sports speed. J Strength Cond Res 19: 349–357, 2005.
8. Gabbett T, Kelly J. Does fast defensive line speed influence tackling proficiency in collision sport athletes. Int J Sports Sci Coach 2: 467–472, 2007.
9. Gabbett T, Kelly J, Ralph S, Driscoll D. Physiological and anthropometric characteristics of junior elite and sub-elite rugby league players with special reference to starters and non-starters. J Sci Med Sport 12: 215–222, 2009.
10. Gabbett T, Ryan P. Tackling technique, injury risk, and playing performance collision sport athletes. Int J Sports Sci Coach 4: 521–533, 2009.
11. Gabbett TJ. Severity and cost of injuries in amateur rugby league: A case study. J Sports Sci 19: 341–347, 2001.
12. Gabbett TJ. Influence of physiological characteristics on selection in a semi-professional first grade rugby league team: A case study. J Sports Sci 20: 399–405, 2002.
13. Gabbett TJ. Incidence of injury in semi-professional rugby league. Br J Sports Med 37: 36–43, 2003.
14. Gabbett TJ. Incidence of injury in junior and senior rugby league players. Sports Med 34: 849–859, 2004.
15. Gabbett TJ. Influence of training and match intensity on injuries in rugby league. J Sports Sci 22: 409–417, 2004.
16. Gabbett TJ. Physiological and anthropometic correlates of tackling ability in rugby league players. J Strength Cond Res 23: 540–548, 2009.
17. Gabbett TJ, Jenkins DG, Abernethy B. Physiological and anthropometric correlates of tackling ability in junior elite and subelite rugby league players. J Strength Cond Res 24: 2989–2995, 2010.
18. Gabbett TJ, Jenkins DG, Abernethy B. Correlates of tackling ability in high-performance rugby league players. J Strength Cond Res 25: 72–80, 2011.
19. Gabbett TJ, Jenkins DG, Abernethy B. Physical collisions and injury in professional rugby league match-play. J Sci Med Sport 14: 210–215, 2011.
20. Gabbett TJ, Jenkins DG, Abernethy B. Relative importance of physiological, anthropometric, and skill qualities to team selection in professional rugby league. J Sports Sci 29: 1453–1461, 2011.
21. Gabbett TJ, Ullah S, Jenkins D, Abernethy B. Skill qualities as risk factors for contact injury in professional rugby league players. J Sports Sci 30: 1421–1427, 2012.
22. Gissane C, White J, Kerr K, Jennings D. Physical collisions in professional super league rugby, the demands on different player positions. Cleve Med J 4: 137–146, 2001.
23. Hendricks S, Lambert M. Tackling in rugby: Coaching strategies for effective technique and injury prevention. Int J Sports Sci Coach 5: 117–135, 2010.
24. Hogarth LW, Deakin G, Sinclair W. Are plyometric push-ups a reliable power assessment tool? J Aust Strength Cond 21: 67–69, 2013.
25. King T, Jenkins D, Gabbett T. A time-motion analysis of professional rugby league match play. J Sports Sci 27: 213–219, 2009.
26. Maulder P, Cronin J. Horizontal and vertical jump assessment: Reliability, symmetry, discriminative and predictive ability. Phys Ther Sport 6: 74–82, 2005.
27. McBride JM, Blow D, Kirby TJ, Haines TL, Dayne AM, Tripplett TN. Relationship between maximal squat strength and five, ten and forty yard sprint times. J Strength Cond Res 23: 1633–1636, 2009.
28. Meir RA, Newton R, Curtis E, Fardell M, Butler B. Physical fitness qualities of professional rugby league players: Determination of positional differences. J Strength Cond Res 15: 450–458, 2001.
29. Norton R, Wilson MA. Rugby league injuries and patterns. N Z J Sports Med 22: 37–38, 1995.
30. Posthumus M, Viljoen W. BokSmart: Safe and effective techniques in rugby union. S Afr J Sports Med 20: 64–70, 2008.
31. Quarrie KL, Hopkins WG. Tackle injuries in professional Rugby Union. Am J Sports Med 36: 1705–1716, 2008.
32. Sykes D, Twist C, Hall S, Nicholas C, Lamb K. Semi-automated time-motion analysis of senior elite rugby league. Int J Perform Anal Sport 9: 47–59, 2009.
33. Van Den Tillaar R, Marques MC. Reliability of seated and standing throwing velocity using differently weighted medicine balls. J Strength Cond Res 27: 1234–1238, 2013.
34. Waldron M, Twist C, Highton J, Worsfold P, Daniels M. Movement and physiological match demands of elite rugby league using portable global positioning systems. J Sports Sci 29: 1223–1230, 2011.
Keywords:

defense; wrestle; contact; collision

Copyright © 2015 by the National Strength & Conditioning Association.