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Movement and physical demands of school and university rugby union match-play in England

Background In England, rugby union is a popular sport and is widely played within schools. Despite the large participation numbers, the movement and physical demands of the sport and how they progress by age have not been explored. Method Ninety-six male rugby union players wore microtechnology devices during six rugby union matches within the education pathway to investigate the movement and physical demands of match-play. To quantify the positional differences and progression by age, data were obtained for participants at the under 16 (U16) (n=31 participants), under 18 (U18) (n=34 participants) and university (n=31 participants) levels. Players were further divided in forwards and backs. Data were analysed using magnitude-based inferences. Results For the movement demands, U16 total distance and ‘striding’ was likely higher for forwards than backs, whereas at U18, unclear differences were observed and from university players the inverse was observed (very likely). In all age groups sprint distance was likely to very likely greater for backs than forwards. Forwards had greater physical demands than backs at all age groups. For consecutive age groups, U16 had a likely higher relative distance than U18, and U18 had a likely lower relative distance than university players. Physical demands were similar across age groups for forwards, and greater for backs at older age groups. Conclusion The movement and physical demands of rugby union players participating in schools (U16 and U18), may not be as expected, however, the findings from university players show a similar pattern to the senior game.


INTRODUCTION
England has the most rugby union players in the world. 1 Recently, collision exposures during schoolboy rugby, in particular tackling, has been questioned. 2 However, limited empirical evidence exists on the physical demands young rugby union players are exposed to in a bid to support or refute these apparent concerns. Data from the senior game has been used to determine the characteristics of rugby union match-play. It shows the game to be an intermittent contact sport exposing players to short-duration, high-intensity activities including high-speed running, sprinting, collisions and tackling interspersed with longer periods of activity at lower intensities. 3 4 The injury incidence during match-play in young rugby union players participating within a regional (professional) academy is 47 per 1000 player-hours, which is greater than school rugby (35 per 1000 player-hours). 5 The injury incidence in both groups is less than previously reported in senior men's professional rugby union matches (81 per 1000

Key messages
What are the new findings?
" Younger rugby union players (under 16 and under 18) appear to have different movement demands by playing position than known in senior players; forwards undertake more running than backs. " The progression by age group suggests backs should focus on preparing for the increase in sprinting (under 16 to under 18) and also striding and physical load (under 18 to university). " The progression trajectory of movement and physical demands for forwards is less clear, while large differences in body mass were observed.
How might it impact on clinical practice in the near future?
player hours). 6 Despite the available injury epidemiology data in youth rugby union, little is known about the demands of the sport at this level. 7 Within rugby union, there are distinct game characteristics for different positional groups; forwards and backs. Quantification of the movement demands by positions for senior professional rugby union competition has been extensively documented via both video 8 9 and more recently, microsensor-based technology. 3 4 It is likely that decisions or opinions surrounding the school and university game are derived from senior data. However, while the quantification of the movement demands from competition in young players have been quantified in other team sports such as rugby league 10 and soccer, 11 there is currently limited information available detailing the match demands of rugby union competition below the senior level. The only study investigating the movement demands in English adolescent rugby union players has been reported for under 20 years old (U20) international players. 12 The movement demands of the U20 international players are similar to those of senior players, 3 4 although this sample is representative of an elite group, thus may not be typical of the movement demands of rugby union below the representative level in England. Furthermore, despite this study 12 providing the first insight into the movement demands of young rugby union players, it is still unclear how the movement demands of the sport are influenced during the progression by age group, which has consequences for player preparation, development, injury prevention and performance.
Player safety, performance, development and participation are all key within young players, thus understanding the load that young rugby union players are exposed to during a match is needed to potentially inform policy and practice. Within England, numerous concurrent playing pathways (ie, education (school and university), club and regional academy) exist both within and across different age groups.
The largest playing pathway for young rugby union players in England is within the school or education programme. 13 Following school, adolescents may continue their education at a university, whereby further participation in rugby union can also take place. When considering the safe progression within rugby union for school boys, it should be considered that school boy rugby is classified based on yearly (eg, U16) and bi-yearly (eg, U18) age categories, whereas university rugby is open age. As such any student studying in higher education is eligible to participate. To date, it is unclear how the movement and physical demands of rugby union change during this transitional period, which has consequences for participation numbers (eg, reduce player drop-off), player performance (eg, recruitment into representative teams) and also injury risk. 14 To this end, the aim of the current study was to determine the differences in the movement and physical demands of match-play in the English educational rugby union player pathway by playing position (ie, forwards and backs) and age group (ie, U16, U18, university).

METHODS Participants
The movement (global positioning system (GPS)) and physical demands (tri-axial accelerometer) of rugby union within the educational pathway were investigated using microsensor technology. Data were collected during six matches from 96 male rugby union players participating across three age categories in England -U16 (n=31 participants), U18 (n=34 participants) and university (n=31 participants). Players were further divided in forwards and backs and participant characteristics are detailed in table 1. The matches were collected from two local independent schools and a university team. The official playing times of matches were 60 (U16), 70 (U18) and 80 (university) min, respectively. Institutional ethics approval was granted and written consent was obtained from the participants or a parent or guardian when a participant was under 18 years of age.

Procedures
During the matches, each participant wore a microsensor device (Optimeye S5, Catapult Innovations, Melbourne, Australia) according to the manufacturer's instructions. The device contained a 10 Hz GPS and a 100 Hz; tri-axial accelerometer, gyroscope and magnetometer. Participants were familiarised with the device during a training session prior to data collection. 10 Hz GPS units have been reported to possess a typical error (coefficient of variation) of 1.9%, 4.7% and 10.5% for total distance, high-speed running (>4.7 ms À1 ) and very high-speed running (>5.56 ms À1 ), respectively. 15 The meanAESD number of satellites during data collection was 14.1AE0.9 with a horizontal dilution of precision of 0.89AE0.17. High within-(0.91%-1.05%) and between-(1.02%-1.10%) unit reliability of the triaxial accelerometer has previously been reported for the Minimax X model, however, no data are currently available for the Optimeye model. 16 At the end of the match, data were downloaded to the manufacturer's software (Catapult Sprint 5.1.7, Catapult Innovations, Melbourne, Australia) and trimmed to include each participant's actual playing time only. Participants whom were substitutes during the match, were only included in the analyses if their playing time exceeded the average substitute playing time. 4 Movement demands Movement demands were determined by total distance and classified in absolute arbitrary velocity zones devised by Hartwig et al 17 using adolescent rugby union players of various ages. The zones were defined as walking (0-1.94 ms À1 ), jogging (1.95-3.33 ms À1 ), striding (3.34-5.83 ms À1 ) and sprinting (>5.84 ms À1 ).

Physical demands
PlayerLoad(PL; arbitrary units (AU)) was used to quantify the physical demands of rugby union match-play. PL is a vector magnitude measure that was calculated from the root mean square of accelerations recorded in the vertical, anteroposterior and mediolateral vectors measured by the 100 Hz tri-axial accelerometer embedded within the microsensor device. 3 In addition, the accumulated PL at slow velocities (<2 ms À1 ; PL slow ) was used to measure the static exertion demands (ie, rucks, mauls, scrums) that are involved within rugby union competition. 3 This method was used to quantify additional external physical demands such as teamsport specific movements and collisions which are unable to be measured using GPS or video-based methods in isolation. 17 Previous research has identified a very large correlation between PL and PL slow with the number of collisions during a rugby union match, with (r=0.785, r=0.701) and without scrums (r=0.727, r=0.799) in forwards. 18 The correlation for PL and PL slow vs number of collisions was found to be moderate and large for backs (r=0.477, r=0.613). 18 Both absolute and relative PL variables were included in the analysis. All relative measures were calculated as the absolute measure divided by the on-field playing time for each player.

Statistical analyses
Descriptive data are presented as the meanAESD. Prior to analysis, all data were log-transformed to reduce bias arising from non-uniformity error and then analysed for practical importance using magnitudebased inferences. 19 Data are presented as Cohen's effect size (ES) statistic with 90% confidence limit (ES; AECL). The chances of the performance measure being lower, similar or greater than the smallest worthwhile difference (0.2x between-participant SD) were calculated using a spreadsheet. 20 The chances that the difference between groups was lower or greater than the smallest worthwhile difference was assessed qualitatively as follows:<0.5%, most unlikely; 0.5%-5%, very unlikely; 5%-25%, unlikely; 25%-75%, possibly; 75%-95%, likely; 95%-99.5%, very likely; >99.5%, most likely. 21 Where the chances of both lower and greater performance measures were >5% the magnitude of difference was reported as unclear.

RESULTS
The meanAESD of GPS and tri-axial accelerometer variables for forwards and backs across U16, U18 and

DISCUSSION
The aim of the current study was to investigate the differences in the movement and physical demands of rugby union match-play in young players by age groups within the English educational pathway for forwards and backs. The key findings of this study were that the between-position differences varied for age groups, and the movement demands of rugby union played at younger age groups are not the same as the senior game. The movement demands that progress by age group were striding and sprinting for backs, whereas several movement and PL variables are lower for U18 compared with both U16 and university forwards. As such, coaches, practitioners and scientists can use these data to physically prepare players in an attempt to reduce the risk of injury and improve physical performance within the rugby union education pathway.
Between position differences Movement demands Differences between positions were typical of the senior professional game 4 at the university level. For example, backs covered a greater total, striding and sprinting distance than forwards. However, below the university level, while some findings were similar (eg, U16 and U18 backs covered greater sprinting distances than forwards), unclear differences in total distance at U18 were observed. Furthermore, in contrast to the senior game, the U16 forwards covered more total, jogging and striding distances than backs. This may be due to a lower level of skill at the younger age group, as recently proposed. 22 As such, the ball may get to the backs less frequently resulting in forwards undertaking more work, although this is yet to be established. This suggests position specific movement demands may not be as profound at youth age categories as in the senior game. 4

Physical demands
Regarding the physical demands, forwards typically accumulated greater PL and PL slow measures across all three age categories in comparison to backs. This is in line with senior elite rugby union, reporting that forwards experience greater physical demands than backs (PL; 590AE80 vs 520AE90 AU and PL slow ; 290AE30 vs 230AE40 AU). 3 Despite these similarities, players participating in the English education pathway appear to be subjected to lower physical demands than professional players 3 which could explain in part, the reduced injury rates in school 5 compared with the professional level. 6 The specific positional demands for forwards are attributed to their prominent role in competing for possession at set pieces and breakdowns, and engage more frequently in tackle contests. 23 The tackle contest, whether a ball-carrier or tackler, has previously been reported to account for 57% of 121 recorded school rugby union injuries during competition, 5 thus understanding potential tackle exposures between positions are of interest to all involved in the game. Given the greater physical demands observed in the current study for the forwards, practitioners should appropriately prescribe training interventions for this positional group, focusing on contact skills 24 alongside the development of both upper and lower body strength and power qualities. 25 The development of those qualities may allow players to better tolerate collision events and concurrently contribute to an improvement in contact ability. 26 Progression by age group Movement demands Understanding the progression of position-specific movement and physical demands across age-groups is also useful for coaches, practitioners and scientists to determine whether players are adequately prepared for the next progression within the playing pathway. Across the three age-categories, unclear differences in total, striding and sprinting distances were observed for the forwards, suggesting the movement patterns may remain similar through the education pathway. For the backs, there were unclear differences in total and relative distance between U16 and U18 age categories while those demands very likely increased between U18 and university. Despite this, we found very likely (165AE101 vs 319AE176 m) increases in sprinting distance between U16 and U18 while unclear differences were observed between U18 and university. This may be an influence of the game context (eg, score, line breaks), given research has shown no differences in sprinting ability between younger and older academy aged rugby union players. 27 As such, the movement demands may warrant further investigation, alongside the game characteristics, to identify potential reasons for any differences in sprinting, or other running activity. This is in addition to understanding the differing trends for forwards and backs. To help prepare backs for the increase in sprinting as they progress from U16 to U18, through appropriate training prescription, U16 players should be exposed to increased sprinting activity for this aspect of competition. 28 29 When considering the progression or change in the movement demands of young rugby union players between age groups, especially when classifying movement by absolute thresholds, 17 a change in player characteristics should also be considered. Previous research 27 has recently highlighted that sprint test performance (5, 10, 20, 40 m) throughout a professional rugby union club (U16, U18, U21) remains stable across academy ages despite increases in body mass. In the current study, maximum sprinting velocity was unclear between ages in both forwards and backs, however, there was a trend for it to increase with age in the backs. In addition, the mean body mass was identical at U16 between forwards and backs (72.0AE10.2 vs 72.0AE9.1 kg) but increased more at U18 (88.9AE10.8 vs 78.8AE10.1 kg) and university (109.8AE8.5 vs 88.2AE7.8 kg) in the forwards compared with the backs. Therefore, the combination of both body mass and sprinting velocity (ie, sprint momentum), may be an important attribute to consider in rugby. 30 Greater player momentum into collision will increase the physical demands 31 of competition as players progress through the pathway.

Physical demands
For forwards there were unclear differences in absolute PL and PL slow across all three age categories, although, when expressed relative to playing time, PLÁmin À1 and PL slow Ámin À1 were found to be very likely and likely lower at U18 compared with both U16 and university competition. Unfortunately, PL is unable to differentiate between the frequency or magnitude of a physical event. As such, U16 may be engaged in more physical collisions of a lower magnitude compared with U18, which would still result in a greater PL accumulation. Similar to the movement demands, the physical demands should now be investigated alongside game characteristics, to further the understanding of rugby union below the senior level. What these data do show is that despite increases in body mass, the absolute physical demands of the English education pathway may not progress in a linear trajectory for forwards.
For the backs, PL was possibly lower at U16 than U18 and was very likely lower at U18 than university. PL slow was found to be unclear between U16 and U18 yet a very likely increase between U18 and university was found. These findings highlight that low-velocity collision based (PL slow ) activities may only increase at the open-age level of competition for the backs, while the overall physical demands (PL) appear to progress across the three age categories. The reader should also be aware of the complexity when quantifying the physical demands. This study failed to quantity the frequency or magnitude of the physical demands, in addition to determining the type of collision (eg, active vs passive shoulder contact). 14 These data suggest backs may be appropriately prepared for the physical demands as they progress from U16 to U18 but may need to improve their capabilities to tolerate the increases in collisions as they progress to open-age (university) competition. The detail of what the collision activity may be, is yet to be established.

Limitations
Despite this study providing the first empirical data to be used by stakeholders when making decisions around rugby union playing and participation pathways within the education system, a small sample size and subsequent lack of further positional breakdowns limits the study. In addition, factors such as match result, standard of opposition and tactics should also be considered in future studies. Furthermore, maturation 32 and developmental (eg, playing experience) differences may influence both the within-and between-game consistency in skill and tactical performance and in turn, impact on the movement demands of education match-play. It should also be acknowledged that PL is a proxy measure of the physical demands and will accumulate during running activity, however, PL slow will only accumulate during lowvelocity activities such as collisions (scrums, tackles, rucks and mauls). Finally, the injury risk of age group progression in addition to the psycho-social factors associated with rugby union also warrant consideration.

CONCLUSIONS
This study demonstrates that the movement demands of rugby union played at younger age groups are not the same as the senior game. Both positional groups appear to have different increasing demands through the age groups, suggesting practitioners should consider including more striding and sprinting for backs and physical exposures (eg, collisions and tackling) for forwards during training. Overall, the movement and physical demands experienced by young players are lower in comparison to professional players. Future research is required to further understand the game of rugby union in relation to young players, and provide data on the demands of the sport in relation to potential injury risk.