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Relationship Between Tests of Physical Qualities, Team Selection, and Physical Match Performance in Semiprofessional Rugby League Players

Gabbett, Tim J.1,2; Seibold, Anthony J.3

Journal of Strength and Conditioning Research: December 2013 - Volume 27 - Issue 12 - p 3259–3265
doi: 10.1519/JSC.0b013e31828d6219
Original Research
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Gabbett, TJ and Seibold, AJ. Relationship between tests of physical qualities, team selection, and physical match performance in semiprofessional rugby league players. J Strength Cond Res 27(12): 3259–3265, 2013—This study investigated the physical qualities that discriminated state-based rugby league players competing for selection in a semiprofessional rugby league team, and determined the relationship between tests of physical qualities and physical match performance in these players. Thirty-two rugby league players (mean ± SD age, 24 ± 3 years) from a Queensland Cup rugby league squad participated in this study. The players performed tests of upper-body strength (3 repetition maximum [RM] bench press; 3RM weighted chin-up), upper-body strength endurance (body-mass maximum repetition bench press), lower-body strength (3RM squat), lower-body power (vertical jump), and prolonged high-intensity intermittent running ability (Yo-Yo intermittent recovery test, level 1). Global positioning system data, sampling at 10 Hz, were collected during 5 Queensland Cup rugby league matches. Selected players had greater (p < 0.05) 3RM squat, 3RM chin-up, body-mass bench press, vertical jump, and Yo-Yo intermittent recovery test performances than nonselected players. After controlling for playing position, players with better 3RM squat performances covered greater total distances (r = 0.98, p < 0.05) including greater distances at low (r = 0.98, p < 0.05) and high (r = 0.97, p < 0.05) speeds. Significant associations (r = 0.96, p < 0.05) were also found between 3RM squat performances and the number of repeated high-intensity effort bouts performed in competition. These findings highlight the importance of lower-body strength, upper-body strength and endurance, and prolonged high-intensity intermittent running ability to team selection in semiprofessional rugby league. Furthermore, our findings suggest that well-developed lower-body strength contributes to effective physical match performance in semiprofessional rugby league players.

1School of Exercise Science, Australian Catholic University, Brisbane, Australia;

2School of Human Movement Studies, The University of Queensland, Brisbane, Australia; and

3Melbourne Storm Rugby League Club, Melbourne, Australia

Address correspondence to Dr. Tim J. Gabbett, tim_gabbett@yahoo.com.au.

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Introduction

Rugby league is an international collision sport, played at amateur, semiprofessional, and professional levels. Several studies have assessed the physical qualities of rugby league players, with performances on physical tests typically increasing with increases in playing level. Data from physical tests have also been used in talent identification programs (10,25) and to provide normative benchmarks for the various rugby league playing positions (7,21,22).

Researchers have assessed the relative importance of physical qualities to playing success by comparing rugby league players who were selected to participate in a team (i.e., starters) with players from the same squad that were not selected (i.e., nonstarters) (7,11). Starters tended to be taller, have faster change of direction speed, and greater playing experience than nonstarters. Moderate to large differences were detected between starters and nonstarters for acceleration, maximum velocity, and estimated maximal aerobic power (7). More recently, the relative importance of physical, anthropometric, and skill qualities to team selection in professional rugby league has been investigated. The players selected to play in the first National Rugby League game of the season were older, more experienced, leaner, had faster 10- and 40-m sprint times, and superior vertical jump performances, maximal aerobic power, tackling proficiency, and dual-task draw and pass ability than nonselected players (15). Collectively, these results suggest a relation between physical fitness and the playing level attained, and that selected physical, anthropometric, and skill qualities may influence team selection in professional rugby league.

Several researchers have explored the relationship between tests of physical qualities and physical match performance in high-intensity intermittent team sports (4,20,26). Rampinini et al. (24) investigated the relationship between tests of physical qualities and match physical performance in professional soccer players. Players with better performance on a repeated-sprint test covered a greater match distance at very high speed and sprinting. Better performance on an incremental field test was also associated with a greater total distance, high-intensity, and very high-intensity running during match play. Castagna et al. (3) and Krustrup et al. (20) found that players with a better performance on the 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 a greater physical performance in soccer competition.

Despite the high collision demand, and the 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 (15). However, it is currently unclear whether these tests of physical qualities (which are all running based) adequately assess the ability of players to perform the repeated high-intensity effort and contact demands of competitive match play. In addition, given the high strength and power requirements of the sport, an association between strength and power qualities and physical match performance might be expected. With this in mind, the purpose of this study was twofold. First, we determined which, if any physical qualities could discriminate between state-based rugby league players competing for selection in a semiprofessional rugby league team. Second, we investigated the relationship between tests of physical qualities and physical match performance in these players.

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Methods

Experimental Approach to the Problem

This study investigated the relationship between tests of physical qualities and physical match performance in semiprofessional rugby league players using a prospective cohort experimental design. Physical qualities of players selected to compete in the first match of the season were compared with those of players not selected. The match demands of semiprofessional rugby league players were compared by separating players into forwards and backs. In addition, the relationship between physical qualities and physical match performance was determined using partial correlations (controlling for playing position). It was hypothesized that physical test performance would be associated with both team selection and physical match performance.

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Subjects

Thirty-two rugby league players (mean ± SD age, 24 ± 3 years) from a Queensland Cup rugby league squad participated in this study. All the participants received a clear explanation of the study, including information on the risks and benefits, and written consent was obtained. All experimental procedures were approved by the institutional ethics committee.

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Physical Testing Battery

The players underwent fitness testing in March as part of their preseason training program for the forthcoming playing season. The physical tests performed were (a) 3 repetition maximum (RM) bench press, (b) 3RM squat, (c) 3RM weighted chin-up, (d) body-mass maximum repetition bench press, (e) vertical jump, and (f) the Yo-Yo intermittent recovery test, level 1. All testing was conducted at the same time of day (∼6.00 PM). The participants were requested to abstain from strenuous physical exercise for 72 hours before testing. The players were also instructed to consume their normal pretraining breakfast and to ensure adequate hydration at the time of testing.

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Upper-Body Muscular Strength

Maximum upper-body strength was assessed using a 3RM bench press exercise performed using a free-weight Olympic-style barbell. The players lowered the bar on to the chest and were required to fully extend their arms for the lift to be counted as a valid trial. The players were not permitted to bounce the bar off their chest, and the feet were required to remain in contact with the ground and buttocks in contact with the bench for the trial to be considered valid. The intraclass correlation coefficient for test-retest reliability and typical error of measurement for the 3RM bench press were 0.88 and 2.2%, respectively.

Given the reported importance of upper-body strength to rugby league playing performance, a second upper-body strength exercise (3RM weighted chin-up) was added to the testing battery to assess the strength of the shoulder extensors. The 3RM weighted chin-up was determined by adding the athlete's body mass to an additional mass that was attached to the athlete. The chin-up test was performed with a supinated grip and begun with an eccentric phase. The trial was considered successful if the athletes fully extended their arms in the eccentric phase and were able to pull their body upward to return to the starting position. The intraclass correlation coefficient for the test-retest reliability and typical error of measurement for the 3RM weighted chin-up were 0.82 and 4.3%, respectively.

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Upper-Body Strength Endurance

Players' strength endurance was assessed using a free-weight bench press using the athlete's body mass as resistance for as many repetitions as possible until fatigue. The intraclass correlation coefficient for test-retest reliability and typical error of measurement for the body-mass bench press to fatigue were 0.80 and 7.3%, respectively.

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Lower-Body Muscular Strength

Maximum lower-body strength was assessed using a 3RM full-squat exercise performed using a free-weight Olympic-style barbell. After warming up with progressively heavier loads, the athlete attempted their 3RM. The players were required to lower their body so that their thighs were past parallel with the floor, and fully extend the hip and knee joints for the trial to be considered valid. The intraclass correlation coefficient for test-retest reliability and typical error of measurement for the 3RM full-squat were 0.93 and 2.3%, respectively.

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Lower-Body Muscular Power

Lower-body muscular power was evaluated by means of the vertical jump test using a Yardstick vertical jump device (Swift Performance Equipment, New South Wales, Australia). Vertical jump height was calculated as the distance from the highest point reached during standing and the highest point reached during the vertical jump. The highest value obtained from 3 trials was used as the vertical jump score. The intraclass correlation coefficient for test-retest reliability and typical error of measurement for the vertical jump test were 0.96 and 3.3%, respectively.

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Prolonged High-Intensity Intermittent Running Ability

The players completed the Yo-Yo intermittent recovery test (level 1) as a measure of prolonged high-intensity, intermittent running ability (19). The test required the players to perform 2 × 20-m runs back and forth at a progressively increasing speed, controlled by a series of audible signals on a compact disk. Between each running bout, the players performed a 10-second active rest period, consisting of 2 × 5-m jogging periods. The total distance covered was recorded as the Yo-Yo intermittent recovery test score. The intraclass correlation coefficient for the test-retest reliability and typical error of measurement for the Yo-Yo intermittent recovery test were 0.98 and 4.9%, respectively (19).

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Physical Match Performance

Global positioning system (GPS) data were collected during 5 Queensland Cup rugby league matches. Movement was recorded by a minimaxX GPS unit (Catapult Innovations, Melbourne, Australia) sampling at 10 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 the upper back of the players.

Data were categorized into (a) movement speed bands, corresponding to low (0–5 m·s−1) and high (>5 m·s−1) speeds (16); (b) collisions (6); and (c) repeated high-intensity effort bouts (11,16). A repeated high-intensity effort bout was defined as ≥3 maximal (≥2.78 m·s−2) acceleration, high speed, or contact efforts with <21 seconds recovery between efforts (11,16). The minimaxX units have been shown to have acceptable validity and reliability (18,23). In addition, the minimaxX units have been shown to offer a valid measurement of tackles and repeated efforts commonly observed in collision sports (6).

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Statistical Analyses

Differences in physical qualities between selected and nonselected players and physical match performance of forwards and backs were compared using an independent t-test and 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 the effect of playing position) were also used to assess the relationship between the tests of physical qualities and physical match performance. Correlations of 0.10–0.29, 0.30–0.50, 0.51–0.70, and >0.71 were considered small, moderate, large, and very large, respectively (17). Based on an alpha level of 0.05, the inclusion of 6 independent variables, and a sample size of 32, our beta level (statistical power) was ≥0.80 for detecting a moderate r2 value from the correlation analysis. The level of significance was set at p < 0.05, and all data are reported as mean ± SD.

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Results

Physical Qualities of Selected and Nonselected Players

The physical qualities of the players selected (and not selected) to compete in the Queensland Cup team are shown in Table 1. Although no significant differences were detected between groups for age, the selected players had significantly greater (p < 0.05, ES = 1.25) playing experience than nonselected players. In addition, selected players had greater (p < 0.05) 3RM squat (ES = 1.02), 3RM chin-up (ES = 1.26), body-mass bench press (ES = 0.89), vertical jump (ES = 1.23), and Yo-Yo intermittent recovery test (ES = 1.45) performances than nonselected players.

Table 1

Table 1

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Physical Demands of Match Play

Backs played greater (p < 0.05) game time than forwards (Table 2). Consequently, the absolute total distance covered, and distance covered at low and high speeds were significantly greater (p < 0.05) for backs. However, forwards covered a greater relative distance (p = 0.06, ES = 0.96), which was predominantly because of a greater relative distance at low speeds (p < 0.05, ES = 1.14). Forwards also engaged in a greater number of collisions per minute of match play (p < 0.05, ES = 2.53) and a greater frequency of repeated high-intensity effort bouts than backs (p < 0.05, ES = 2.59).

Table 2

Table 2

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Relationship Between Physical Qualities and Physical Match Performance

The relationship between tests of physical qualities and physical match performance, controlling for playing position, is shown in Table 3. The players with better 3RM squat performances covered greater total distances (r = 0.98, p < 0.05) including greater distances at low (r = 0.98, p < 0.05) and high (r = 0.97, p < 0.05) speeds. Significant associations (r = 0.96, p < 0.05) were also found between 3RM squat performances and the number of repeated high-intensity effort bouts performed in competition. No significant associations were found between any other physical quality and physical match performance (Table 3).

Table 3

Table 3

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Discussion

This study investigated the physical qualities that discriminated state-based rugby league players competing for selection in a semiprofessional rugby league team. We also determined the relationship between tests of physical qualities and physical match performance in these players. The players selected to compete in the semiprofessional team had greater lower-body strength and power, upper-body strength, and endurance, and prolonged high-intensity intermittent running ability than nonselected players. In addition, after controlling for playing position, measures of lower-body strength were significantly and positively associated with the distance covered at low and high speeds and the number of repeated high-intensity effort bouts performed in competition. These findings highlight the importance of lower-body strength, upper-body strength and endurance, and prolonged high-intensity intermittent running ability to team selection in semiprofessional rugby league. Furthermore, our findings suggest that well-developed lower-body strength contributes to effective physical match performance in semi-professional rugby league players.

Selected players had a significantly greater playing experience than nonselected players. Playing experience has previously been shown to be a significant predictor of playing performance and success in senior rugby league players (8), and suggested to be a critical variable determining selection into subelite (10) and elite (15) first-grade rugby league teams. It has also been shown that players with ≥150 matches National Rugby League experience had superior tackling technique than players with <150 matches National Rugby League experience (8), providing further support to the fact that sporting expertise develops, at least in part, as a result of accumulated playing experience.

We found greater upper-body strength (3RM chin-up) and endurance (body-mass bench press), lower-body strength (3RM squat) and power (vertical jump), and prolonged high-intensity intermittent running ability in selected players than in nonselected players. These findings are generally consistent with those of other rugby league studies that have found progressive improvements in strength (2), strength endurance (2), muscular power (7,11), and prolonged high-intensity intermittent running ability (1,15) with increases in the playing standard. Collectively, these findings highlight the centrality of well-developed physical qualities to team selection in semiprofessional rugby league players.

Significant and very large (r = 0.96) associations were found between lower-body strength and the frequency of repeated high-intensity effort bouts performed; when controlling for playing position, players with better full-squat performances performed more repeated high-intensity effort bouts in competition. These findings demonstrate the importance of lower-body muscular strength to physical match performance in semiprofessional rugby league players. The very large association between lower-body strength and the number of repeated high-intensity effort bouts performed in competition is of interest, particularly given the lack of association between measures of upper-body strength, strength endurance, and prolonged high-intensity intermittent running ability and repeated-effort performance. Previous studies have reported a significant, but modest association (r = 0.38) between measures of lower-body muscular power and tackling proficiency in rugby league players (13). Given the large amount of collision activity performed in repeated high-intensity effort bouts (11), the present findings highlight the importance of lower-body strength to repeated-effort performance in rugby league. Although a significant correlation does not imply cause and effect, these results may suggest that improvements in lower-body strength may facilitate greater repeated high-intensity effort work rates in semiprofessional rugby league. Moreover, although important for team selection, our findings suggest that upper-body strength, strength endurance, and prolonged high-intensity intermittent running ability, contribute minimally to repeated-effort performance in rugby league players.

Although previous researchers have investigated relationships between selected running qualities (e.g., speed, repeated-sprint, and prolonged high-intensity intermittent running) and physical match performance (4,20,26), to our knowledge, this is the first study to assess the relationship between strength qualities and physical match performance in a prolonged high-intensity intermittent team sport. The unique collision demands of rugby league match play make strength a requisite quality for competitors to effectively tolerate the blunt force trauma that occurs in tackles and the physical stress associated with wrestling activities. Although a significant association between lower-body strength and distances covered at both low and high speeds was an unexpected finding, greater absolute strength is likely to have resulted in players performing these wrestling and grappling activities at a lower relative intensity than weaker players. Consequently, the players were likely to have greater physical reserves to devote to the running demands of competition.

We found no relationship between Yo-Yo intermittent recovery test performance and any measure of physical match performance. Several researchers have shown that competitors from prolonged high-intensity intermittent team sports (e.g., soccer), with better performance on the Yo-Yo intermittent recovery test, performed more running and high-intensity activity during match play (3,20). A possible explanation for the discrepant findings of the present and previous investigations may lie in the contact nature of rugby league relative to soccer. Indeed, although the running demands of rugby league are relatively low in comparison to other prolonged high-intensity intermittent team sports, the physical demands of rugby league are significantly increased through the large amounts of collisions, tackling, and wrestling that occur during match play. Clearly, when players are engaged in these contact efforts, they are unable to cover great distances, although the energetic costs of these activities are likely to be extremely high. The present results, coupled with the findings of others (1), suggest that although the Yo-Yo intermittent recovery test provides an insight into the physical qualities important for selection into a rugby league team, it explains little of the variance in locomotor performance during rugby league match play. A game-specific measure of repeated-effort ability that incorporates sprinting and collisions is likely to provide a more realistic assessment of the ability of players to complete the most intense repeated-effort demands of rugby league match play.

Although we limited our investigation to the physical qualities that discriminated selected and nonselected players, it has also been shown that various technical and tactical skill qualities can discriminate rugby league players of higher and lower abilities (9,15). Moreover, these skill qualities have been reported to be positively associated with game-specific performance measures (e.g., line break assists and try assists) (14). However, it is currently unclear whether skill qualities influence the physical match performance of team sport players with previous authors showing that training-induced improvements in perceptual skill (i.e., decision making) had minimal effect on the physical demands of game-based activities in elite soccer players (12). Further studies investigating the relationship between rugby league skill qualities and physical match performance are clearly warranted.

In conclusion, we investigated the physical qualities that discriminated rugby league players competing for selection in a semiprofessional rugby league team and determined the relationship between tests of physical qualities and physical match performance in these players. The players selected to compete in the semiprofessional team had greater lower-body strength and power, upper-body strength and endurance, and prolonged high-intensity intermittent running ability than nonselected players. In addition, after controlling for playing position, lower-body strength was significantly and positively associated with the distance covered at low and high speeds and the number of repeated high-intensity effort bouts performed in competition. These findings highlight the importance of lower-body strength, upper-body strength and endurance, and prolonged high-intensity intermittent running ability to team selection in semiprofessional rugby league. Furthermore, our findings suggest that well-developed lower-body strength contributes to effective physical match performance in semiprofessional rugby league players.

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Practical Applications

This is the first study to document the physical demands of forwards and backs competing in semiprofessional rugby league match play. As only 1 team was investigated, it would have been ideal to gain a larger sample size that included all teams within a competition. However, each team conducts different tests of physical qualities, and because of the competitive nature of sport, it is very rare that teams share their testing results. Despite this potential limitation, the results of this study have relevance to the applied sport scientist and strength and conditioning coach. The data presented in this study can be used to develop game-specific conditioning activities that prepare players for the most demanding passages expected during these matches.

Second, our results demonstrate that measures of lower-body power, upper-body strength and endurance, and prolonged high-intensity intermittent running ability discriminate successful and less successful rugby league players, but are not associated with running, collision, or repeated-effort performance. These findings suggest that enhancing these physical qualities is likely to improve the likelihood of selection into a semiprofessional rugby league team. However, these improvements are unlikely to be associated with physical match performance. It should also be noted that these findings are likely to be most relevant to the population from which they are derived so that they may not be applicable to teams that have a poor balance between physical and skill qualities.

Finally, well-developed lower-body strength was associated with better running and repeated-effort performance during rugby league match play. Improvements in lower-body strength may facilitate greater running and repeated high-intensity effort work rates in semiprofessional rugby league players.

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Keywords:

fitness; collision sport; match analysis; team sport; repeated high-intensity effort

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