Rugby league is a multiple sprint collision sport. Rugby league athletes require high levels of speed, strength, power, and agility to play the game at a semiprofessional or professional level (3,4,6,20,22,27,28). These attributes are essential in helping the athlete deal with the variety of movement patterns within the game, which includes short sprints, quick changes in direction, jumping and landing, spinning the body in and out of tackles, upper- and lower-body tackling, and short bouts of wrestling (10,24–26).
Rugby league players use both aerobic (to provide adenosine triphosphate (ATP) for the duration of the game, including recovery between anaerobic bouts) and anaerobic energy systems (for each high-intensity activity) (1,22), with the game lasting for 80 minutes and players covering distances of 7–10 km depending on position and the pace of the game (25,26). These distances are made up of short-duration high-intensity efforts followed by longer periods of low-intensity activities (25,26). Athletes must perform multiple short sprints ranging from 6–8 m for forwards and 8–12 m for backs, the frequency of these sprints ranges from 43 to 50.6% per game between forwards and backs, respectively (1,25). Up to 40 high force collisions have to be absorbed by each player per game, followed by short durations of wrestling with their opponent, which demands high levels of concentric, eccentric, and isometric force production (9).
A body of normative data covering amateur, junior sub-elite and elite, and senior sub-elite and elite rugby league players has been mainly carried out in Australia (1,3,4,6,10,13,20,22,24,26–28), with only 1 published study on English Senior Super League players (11). In the under-19 age group, average sprint times for the backs over distances of 10, 20, and 40 m, range from 2.19 ± 0.09 seconds, 3.53 ± 0.12 seconds, and 6.01 ± 0.16 seconds, respectively, with the forwards demonstrating similar 10-m and 20-m performances (2.19 ± 0.09 seconds and 3.57 ± 0.11 seconds, respectively), but slower 40-m sprints (6.20 ± 0.19 seconds) (14). In the second grade age group (19 years and older), average sprint times for the backs (2.08 ± 0.11 seconds, 3.34 ± 0.12 seconds, and 5.81 ± 0.17 seconds) over 10, 20, and 40 m were consistently faster than the forwards (2.14 ± 0.05 seconds, 3.50 ± 0.07 seconds, and 6.09 ± 0.15 seconds) (15).
The times recorded for the under 19 group and the over 19 group showed an increase in speed for the over 19 suggesting improved speed and power gains as the athlete matures.
This trend was also observed in jump performances of the 2 age groups (under 19 range 37.9–40.0 cm, over 19 ranges 41.0–42.9 cm) (15) showing an increase in height jumped with age. Positional differences within a rugby league team equate to changes in physiology between individual playing positions. King et al. (24) reported that backs covered the greatest distance (6,265 ± 318 m), adjustables covered 5,908 ± 158 m, and forwards covered the least distance with (4,310 ± 251 m). In contrast, however, Sykes et al. (30) reported that English forwards covered a greater distance per game than backs (8,688 ± 405 m vs. 8,142 ± 630 m), possibly highlighting different characteristics between the games in Australia and England. The discrepancies in distances recorded between the 2 studies may be partly explained by the different match analysis protocols (hand notation compared with a semiautomated system), weather conditions, team tactics, playing style of opposition, and team competitiveness. King et al. (24) and Sykes et al. (30) reported similar trends between forwards and backs with forwards are involved in a greater number of tackles per game than backs. In contrast, backs spend more time sprinting over larger distances as their position on the field allows them to use more space (24,30). It is also worth noting that even though forwards cover less distance than the backs, the greater number of involvements in tackles is likely to add to their total work resulting in high levels of fatigue. These positional differences between forwards and backs are evident in the physiological makeup of the 2 groups. Forwards tend to have greater body mass and higher absolute strength levels compared with backs. Backs tend to be faster and have superior jump ability; these differences are likely because of the previously discussed variations between the playing positions (3,4,9,10,14,15,23,24,26). In addition, research correlating maximal squat strength with improved sprint and jump height capabilities has indicated that the greater an athlete's relative squat strength the better sprint and jump performance the athlete can achieve (11,25).
Because of the absence of research regarding English junior rugby league players, the aim of the research was to identify any differences in strength, power, and speed performance between forwards and backs in English junior elite rugby league players and to determine any relationships between strength and sprint and jump performances. In addition, these data will be useful for coaches and strength and conditioning coaches when conducting a needs analysis of their junior athletes, especially in England. It was hypothesized that forwards' absolute strength would be greater than the backs' as a result of greater stature, but that relative strength would be comparable and that backs would demonstrate a higher jump height and faster sprint performances in comparison to the forwards, in line with previous research.
Experimental Approach to the Problem
High-level under 20 English rugby league forwards and backs performed a range of performance tests, over 2 days (previous testing had determined reliability of these measures), to determine maximal sprint (10, 20, and 40 m), jump, 1 repetition maximum (1RM) bench press, and 1RM back squat performances. This permitted both comparisons of performances between forwards and backs and the determination of associations between performance measures for the whole squad.
A squad of 24 elite junior rugby league players (age 18.70 ± 0.90 years, body mass 86.4 ± 9.93 kg, height 178.47 ± 6.97 cm) playing in the under 20 Super League competition were investigated, comprising 12 forwards and 12 backs. All subjects had just completed an off season period comprising 2 weeks of complete rest followed by 2 weeks of training before returning for preseason training. Ethical approval was granted from the university and written, informed consent was provided by the participants. Parents' approval was gained for participants under the age of 18.
During the initial testing session, body mass, height, countermovement jump (CMJ), and sprint tests (10, 20, and 40 m) were performed, with maximal strength testing performed 48 hours later. Previous testing within this population had revealed a high reliability (intraclass correlation coefficients [ICCs]) for countermovement vertical jump (r ≥ 0.91), sprint (r ≥ 0.97), and 1RM (r ≥ 0.97) performances. Data were divided into two groups (forwards and backs) to permit positional comparisons and pooled to determine relationships between performance characteristics.
A countermovement jump (CMJ) was performed as an indicator of power output, using a contact mat (Just Jump; Probotics, Inc., Huntsville, AL, USA). Subjects were asked to perform the jump with their hands on their hips, throughout the movement, to rapidly descend to a self-selected depth and then to jump as high as possible from that position, with no pause between the eccentric and concentric phases of the movement. If an obvious pause occurred, the athlete performed a tuck jump, or their hands left their hips, they were instructed to rest for 90 seconds and then repeat the trial. Subjects performed 3 trials with 90 seconds of rest between each effort to establish repeatability. The athlete's best score was used for further analysis.
Subjects performed a 40-m sprint on a third generation Astroturf sports pitch surface (Astroturf, AMB Sports Ltd, Kent, UK) wearing regular running trainers. Each sprint was performed with subjects instructed to ensure maximal effort; before this, participants performed a 15-minute dynamic warm-up and 3 practice sprints at approximately 70, 80, and 90% of maximum sprints. Times for 10, 20, and 40 m were recorded using Brower timing gates (Brower TC-timing system; Brower Timing Systems 12660, Draper, UT, USA). A standardized starting position of 0.5 m behind the line was used for the sprints to prevent any early triggering of the timing gates, and no countermovements were permitted.
The 1RM bench press and back squat were selected as they are commonly acknowledged as reliable and valid measures of strength and were exercises that all athletes were accustomed to. During the bench press, athletes were instructed to lower the bar down to the chest and then push the barbell off the chest to lock the arms out to return to the start position, in one smooth continuous motion, following a standardized protocol (2), using a standard bench (Olympic flat bench) and Olympic bar (7 ft Olympic bar and weights; York Barbell Company, York, PA, USA). In addition, lifts were recorded using a camcorder (JVC Model: GZ-MG21EK, JVC, London, UK), from the sagittal plane, to confirm that each subject had achieved the 90° angle required for the test.
All statistical analyses were conducted using SPSS version 16.0 (SPSS version 16.0, IBM, Portsmouth, Hampshire, UK). Reliability of the CMJ tests was determined via ICCs. Independent t-tests were carried out to identify differences in performances between backs and forwards. Pearson's correlations were performed to identify relationships between jump height and absolute and relative squat strength; furthermore, Pearson's correlations were performed to identify relationships between sprint performances and absolute and relative squat strength.
The ICCs confirmed a high degree of reliability between trials for the vertical jump test (r = 0.964, p < 0.001). Although backs were slightly shorter and lighter than the forwards, the t-tests revealed that there were no significant (p > 0.05) differences in body mass, height, and age of forwards (90.08 ± 11.72 kg, 180.13 ± 7.65 cm, and 18.75 ± 1.06 years) and backs (82.75 ± 6.28 kg, 176.83 ± 6.10 cm, and 18.67 ± 0.78 years).
Sprint and Jump Performance
Backs were significantly faster than the forwards over 10 m (1.99 ± 0.06 seconds, 2.06 ± 0.10 seconds; p = 0.011), 20 m (3.26 ± 0.07 seconds, 3.39 ± 0.17 seconds; p = 0.002), and 40 m (5.55 ± 0.13 seconds, 5.80 ± 0.26 seconds; p = 0.0001) (Figure 1). There were no significant differences (p > 0.05) in CMJ height between backs (50.60 ± 5.02 cm) and forwards (50.58 ± 7.06 cm).
Comparisons of absolute bench press strength and squat strength between the 2 groups demonstrated greater bench press and squat (110.00 ± 15.80 kg, 140.21 ± 26.21 kg) in the forwards compared with backs (101.67 ± 9.13 kg, 132.71 ± 9.38 kg), although this was not statistically significant (p > 0.05). Further evaluation of squat strength relative to body mass also revealed no significant differences (p > 0.05) between backs (1.61 ± 0.13 kg/kg) and forwards (1.56 ± 0.20 kg/kg).
Pearson's correlations revealed a moderate correlation (r = 0.42, p = 0.01) between relative back squat strength and jump height, but a stronger correlation (r = 0.57, p < 0.001) between absolute strength and jump height (Figure 2).
Relationships between absolute strength and sprint times over 10, 20, and 40 m, were weak and nonsignificant (r = −0.25, −0.28, and −0.2; p < 0.05, respectively). In contrast, there were moderate inverse correlations between relative squat strength sprint times (r = −0.45, −0.46, and −0.44; p < 0.01) (Figures 3–5).
In contrast to previous research and the hypotheses, the only statistically significant differences observed within the current study were the quicker sprint times of the backs compared with the forwards, with no significant differences in physical stature, strength, or jump performance.
Despite positional differences and in contrast to the hypothesis body mass and height were very similar between forwards (90.08 ± 11.72 kg; 80.13 ± 7.65 cm) and backs (82.75 ± 6.28 kg; 176.83 ± 6.10 cm). In comparison, Australian data on under 19 sub-elite rugby league forwards show a similar body mass to their English counterparts (89.4 ± 10.8 kg), although in contrast Australian backs tend to be considerably lighter than the English backs (74.2 ± 6.5 kg) (14). This disparity may be due in part to different strength and conditioning practices and altered match characteristics and intensities between northern hemisphere and southern hemisphere rugby leagues. In addition, differences in growth and maturation rates between players of this group may skew the results in comparison to a senior squad.
Sprint performances showed backs to be significantly (p ≤ 0.011) quicker over all 3 distances, (10 m, 1.99 ± 0.6 seconds; 20 m, 3.26 ± 0.7 seconds; 40 m, 5.55 ± 0.13 seconds), compared with the sprint performances of the forwards (2.06 ± 0.10 seconds, 3.39 ± 0.17 seconds, and 5.80 ± 0.26 seconds). In comparison, Gabbett (15) reported slower 10-m (Backs, 2.08 seconds; Forwards, 2.19 seconds), 20-m (Backs, 3.53 seconds; Forwards, 3.57 seconds), and 40-m sprint performances (Backs, 6.01 seconds; Forwards 6.20 seconds) in Australian under 19 players, although they were described as sub-elite.
Forwards' and backs' mean vertical jump heights were almost identical (50.58 ± 7.06 cm vs. 50.60 ± 5.02 cm, respectively). These data are in contrast to the findings of Gabbett (15) and Comfort et al. (12) who showed backs to have greater vertical jump performances compared with forwards, although this may be explained by the lack of differences in squat strength between forwards and backs in this study. In addition, the vertical jump height of the English elite under 20 forwards and backs were superior to the performances reported by Gabbett (15) for Australian sub-elite under 19 forwards and backs (37.9 ± 4.8 cm and 40.0 ± 4.9 cm, respectively). Both groups performed a CMJ; however, Gabbett (15) used a chalk mark on the wall to assess jump height, which may have affected the heights recorded in their study.
Strength performance revealed that the forwards were stronger in the bench press and squat (110.00 ± 15.8 kg and 140.21 ± 26.21 kg, respectively) in comparison to the backs (101.67 ± 9.13 kg and 132.71 ± 9.38 kg, respectively), although this was not statistically significant (p > 0.05). When strength performances were scaled for body mass, the observed differences between positions were reduced further for both the bench press (Forwards, 1.23 ± 0.08 kg/kg; Backs, 1.22 ± 0.10 kg/kg) and the squat (Forwards, 1.61 ± 0.13 kg/kg; Backs, 1.56 ± 0.20 kg/kg). Comparisons with bench press (143.3 ± 15.4 kg) and squat (182.5 ± 23.6 kg) strength in young (<24 years) Australian athletes competing in the National Rugby League (7) revealed a deficit in strength in the athletes in this study; this difference in strength may be explained by age difference which may be as much as 6 years, along with a similar difference in years of training between athletes in both studies. The lack of differences between positions in this group may be because of the fact that Sykes et al. (30) identified similar distances covered by English forwards covered a greater distance per game than backs (8,688 ± 405 m vs. 8,142 ± 630 m, respectively), which is in stark contrast to the distances reported by King et al (24) in Australian athletes, with backs covering the greatest distance (6,265 ± 318 m) compared with the forwards (4,310 ± 251 m). The authors acknowledge that this study is limited in the fact that direct comparisons between Australian and English athletes, using identical protocols fitness tests and that time motion analysis data has not been included. It is suggested that future research should compare both physical characteristics and match analysis data, using the same protocols to identify differences in physical performance to identify if these are related to match analysis data; furthermore, direct comparisons between rugby league performances in the northern and southern hemisphere is recommended.
Interestingly, correlation analysis revealed a stronger correlation (r = 0.57, p < 0.001) between absolute strength and jump height than relative strength (r = 0.42, p = 0.01), even though the athlete has to accelerate their body mass when jumping which would imply a stronger relationship to relative strength. In contrast, relationships between absolute strength and sprint times over 10, 20, and 40 m were weak and nonsignificant (r = −0.25, −0.28, and −0.2; p < 0.05, respectively), whereas relative strength demonstrated moderate inverse correlations between relative squat strength sprint times (r = −0.45, −0.46, and −0.44; p < 0.01) across 10, 20, and 40 m, respectively. This is in line with the previous research correlating maximal squat strength improved sprint performances (11,25,33), which is likely explained because of the fact that high ground reaction forces are associated with sprint performance (31,32,34).
The importance of lower limb strength in improving both jump and sprint performance is crucial in enhancing acceleration over short distances (11,25,33). Developing squat strength relative to body mass is a fundamental requirement of multiple sprint sports where acceleration is a key component. In conclusion, it is recommended that strength and conditioning coaches develop training programs that maximize squat strength, as part of a periodized training regime, to enhance the acceleration capabilities over distances of 10–40 m, irrespective of playing position, especially in developing athletes as relative strength seems to differentiate between sprint and jump performance.
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