Rugby league is a collision sport played internationally at junior and senior level. The game is intermittent in nature, characterized by bouts of high-intensity running, collisions, and tackling, separated by periods of lower intensity activity (14,18). 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 (12). Rugby league players require well-developed aerobic fitness, speed, muscular strength and power, and agility to compete at an elite level (16). An understanding of how these physical qualities relate to specific rugby league skills is essential for the development 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 (11,17). 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 (13). Generally, forwards will perform an average of 39 tackles, compared with the backs who perform an average of 16 tackles per match (13). 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 (6). 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 (7). Therefore, the ability to perform a well-executed tackle is critical for the player to “win” the contact contest.
Several studies have examined the physiological and anthropometric correlates of tackling ability in subelite and professional rugby league players (8–10). Well-developed acceleration (over a 10-m sprint) and lower-body muscular power are associated with superior tackling ability in elite junior and professional rugby league players (8–10). Furthermore, lower- and upper-body strength, as well as upper-body power has been shown to be significantly related to tackling ability in semiprofessional rugby league players (unpublished observations). Although these findings provide important information on the relationship between selected physical qualities and tackling ability, significant correlations do not imply cause and effect. It has been proposed that if an appropriate amount of time was devoted to the skill of tackling, then improvements in muscular strength and power may transfer to improvements in tackling ability (8–10). However, to date, no study has examined if improvements in muscular strength and power transfer to improvements in tackling ability. This study examined the influence of a strength and power program on tackling ability in an aim to provide insight into the possible mechanisms for eliciting improvements in tackling ability. It was hypothesized that players who experienced the greatest adaptions in muscular strength and power would demonstrate the greatest improvements in tackling ability.
Experimental Approach to the Problem
To test our hypothesis, a repeated-measures experimental design was used to evaluate changes that occurred in muscular strength and power qualities as well as tackling ability after an 8-week training intervention. The players underwent tests of upper- and lower-body strength and power as well as an assessment of tackling ability before, and after an 8-week strength and power training program. Using a median-split technique, players were then divided into “responders” or “nonresponders” in each strength and power test based on the results of the strength and power testing. Pearson product-moment correlations were also used to assess the relationship between training-induced changes in strength and power and tackling ability.
Twenty-four senior (aged >18 years) rugby league players (mean ± SD age, 23.4 ± 3.1 years) participated in this study. All players were from the same rugby league club. Players were classified as semiprofessional as they 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 the initial 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.
Upper- 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 as 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 using a standard 20-kg Olympic barbell, with 3–5 minutes of 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 a below parallel thigh position (i.e., they descended to a position where the hip crease dropped below the knee). 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. Relative upper- and lower-body strength was calculated by dividing the 3RM of the bench press and squat by the player's body mass.
Lower- and upper-body peak power was assessed with the players performing a countermovement jump (CMJ) and plyometric push-up on a force platform with a sampling rate of 500 Hz (Kistler 9290AD Force Platform; Kistler, 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 used for analysis. 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 plyometric push-up, the players were instructed to place their hands on the force platform while 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 plyometric push-up were 0.97 and 3.8%, respectively.
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 (8–10). The drill was conducted in a 10-m grid with video cameras (Canon Legria HV40, Tokyo, Japan) on the left, right, and rear of the drill. The participants performed 6 consecutive tackles, 3 on the right shoulder and 3 on the left shoulder, on another participant of similar height and mass. The drill was performed at the start of a training session so that the participants were in a nonfatigued state. Tackling ability was assessed by a sport scientist using standardized technical criteria that has been used in previous studies of tackling ability in rugby league players (8–10).
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 criteria 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, Dunedin, New Zealand). The intraclass correlation coefficient for test-retest reliability and typical error of measurement for tackling ability were 0.88 and 3.9%, respectively. The intraclass correlation coefficient for test-retest reliability and typical error of measurement for the movement velocity immediately before contact were 0.94 and 2.9%, respectively.
All players underwent an 8-week strength and power training block as part of their preseason training. The players completed 3 strength and power training sessions per week. Because of the players being semiprofessional and the lack of facilities within the club, it was not possible to have the players perform their strength and power sessions separate to their field sessions. As a result, the players were required to perform skill-based training as part of the same training session as the strength and power training. All the players performed the resistance program consisting of 3 sets of 3–6 repetitions. The strength and power program used heavy compound movements combined with explosive exercises (Table 1).
Data were tested for normality using a Shapiro-Wilk test. We analyzed (1) the effect of the training program on strength, power, and tackling ability; (2) the magnitude of improvements in tackling ability in players who did (i.e., responders) and did not (i.e., non-responders) show positive adaptations to the strength and power program, and (3) the relationship between training-induced changes in strength and power and changes in tackling ability. First, pre-to post-training changes in strength, power, and tackling ability for the entire group were determined using a paired t-test. Second, players were divided into responders or nonresponders in each strength and power test based on the median split of the results of the strength and power testing. A 2-way group (responders vs. nonresponders) × time (pretraining vs. posttraining) repeated-measures analysis of variance was used to examine changes in strength, power, and tackling ability. Cohen's effect size (ES) statistic (4) was also used to determine the magnitude of any differences between pre- and post-training testing and between groups. 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 (2). Finally, Pearson product-moment correlation coefficients were used to determine the relationships among changes in muscular strength and power and tackling ability. The level of significance was set at p ≤ 0.05, and all data are reported as mean ± SD.
Changes in Strength, Power, and Tackling Ability
Table 2 shows the changes in muscular strength and power, and tackling ability after 8 weeks of training. A small difference in squat (p ≤ 0.01; ES = 0.47) and a trivial difference in bench press (p ≤ 0.01; ES = 0.14) were found between the pre- and post-training intervention. Similarly, there was a significant improvement in strength relative to body mass. A moderate change was found in squat relative to body mass (p ≤ 0.01; ES = 0.69) and a trivial difference in bench press relative to body mass (p ≤ 0.01; ES = 0.14). A significant improvement in both CMJ (p ≤ 0.01; ES = 0.27) and plyometric push-up (p ≤ 0.01; ES = 0.46) muscular power were also found. A small significant improvement in tackling ability was also found (p = 0.02; ES = 0.26).
Relationship Between Strength and Power Qualities and Tackling Ability
Table 3 shows the relationships between changes in strength and power qualities and changes in tackling ability. The strongest correlates of change in tackling ability were change in 3RM squat (r = 0.60; p < 0.01) (Figure 1) and squat relative to body mass (r = 0.54; p < 0.01) (Figure 2).
Responders vs. Nonresponders
The changes in strength and power qualities in the responders and nonresponders are shown in Table 4. The responders had significantly greater (p < 0.01) improvements in all strength and power tests. The magnitude of differences ranged from large to very large.
Table 5 shows the relationships between improvements in tackling ability and strength and power measures in the responders and nonresponders. Players with the greatest improvements in the squat test (i.e., responders) had significantly greater improvements in tackling ability than the nonresponders (p = 0.04; ES = 0.90). Similarly, players with the greatest improvements in relative squat strength also had significantly larger improvements in tackling ability (p = 0.04; ES = 0.90). A small difference in tackling ability (albeit nonsignificant) was found between the highest and lowest responders for CMJ peak power (p = 0.17; ES = 0.56). Only trivial to small relationships were found among bench press, relative bench press, plyometric push-up, and tackling ability.
This is the first study to examine if improvements in muscular strength and power transfer to improvements in tackling ability. It was hypothesized that players who experienced the greatest adaptions in muscular strength and power would demonstrate the greatest improvements in tackling ability. In support of our hypothesis, we found that players with the greatest improvements in both absolute and relative squat had significantly greater improvements in tackling ability than their nonresponding peers. In addition, significant associations were found between improvements in lower-body strength and improvements in tackling ability. From a practical perspective, these findings demonstrate that improvements in lower-body strength are likely to lead to improvements in tackling ability in rugby league players.
This study found that the players who had the greatest improvements in lower-body strength and power also had the greatest improvements in tackling ability. These findings are in partial agreement with our hypothesis that players who experienced the greatest adaptions in muscular strength and power would demonstrate the greatest improvements in tackling ability. From the results of previous research, authors have speculated that improvements in lower-body strength and power could transfer into improvements in tackling ability (8–10). The results of this study suggest that this is the case. Interestingly, the players who experienced the greatest improvements in upper-body strength and power did not experience any greater improvements in tackling ability than low responding players. This is somewhat surprising given that upper-body strength and power has been shown to be associated with tackling ability in semiprofessional rugby league players (unpublished observations).
There are numerous possible mechanisms for the superior improvements in tackling ability in the players with greater improvements in lower-body strength and power. The improvement in lower-body strength and power may have enhanced the players' ability to exert power into the tackle allowing them to improve leg drive through the tackle. Improvements in change of direction speed and acceleration may offer another possible explanation for the improvements in tackling ability. Gabbett (8) reported that better tacklers had greater acceleration and change of direction speed and suggested that change of direction speed may affect how well players position themselves before making contact. Studies have found that increased lower-body strength and power is associated with improved acceleration and change of direction speed (3,5,15). Future research examining changes in tackling ability should also examine the changes in acceleration and change of direction speed.
The strongest correlates of change in tackling ability were improvements in 3RM squat (r = 0.60) and squat relative to body mass (r = 0.54). The coefficient of determination (r2) for the 3RM squat and squat relative to body mass were 36 and 29%, respectively. Therefore, 64–71% of the variance in improved tackle ability is explained by factors in addition to, or other than improvements in lower-body strength. While this study provides an important step in explaining how changes in strength influence tackling ability, it must be acknowledged that additional factors (e.g., specific skill coaching and skill rehearsal) may explain a greater proportion of the change in tackling ability.
A small and significant improvement in tackling ability was found after 8 weeks of training. These findings are similar to an earlier study examining tackling ability in high-performance rugby league players which found a small but nonsignificant improvement in tackling ability after 3 months of preseason training (7). The combined results from these studies demonstrate that tackling ability can be improved in rugby league players in a relatively short amount of time provided that players receive an adequate training stimulus.
One limitation of this study is that training age or playing experience was not taken into consideration. Previous research has found that more experienced players have better tackling ability than less experienced players, suggesting that less experienced players have greater scope for improving tackling ability than experienced players (7,10). Furthermore, Baker and Newton (1) found that less experienced weaker players experienced greater improvements in strength and power than stronger more experienced players. Future studies examining the effect of strength and power training on tackling ability should examine the difference between experienced and less experienced players.
In conclusion, this is the first study to examine the influence of improvements in muscular strength and power on tackling ability in rugby league players. These findings demonstrate that increases in lower-body muscular strength, and to a lesser extent, muscular power, contribute to improvements in tackling ability in semiprofessional rugby league players. Further research examining the relationship between muscular strength and power training on tackling ability in other competitive levels, such as professional and junior players, is warranted.
Of particular note to rugby league coaches, this study demonstrates that significant improvements in tackling ability can be elicited in a relatively short amount of time. Furthermore, this study has found that improvements in lower-body muscular strength and power are related to improvements in tackling ability in semiprofessional rugby league players. This research highlights the importance of allowing adequate time for strength training during the preseason phase.
The findings of this study demonstrate that improvements in lower-body strength are likely to lead to improvements in tackling ability in rugby league players. It can be assumed that as long as the technical aspects of tackling ability 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 the tackling ability of players.
There was no financial assistance for this research. The authors thank all players and coaching staff who participated in this study.
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