Science of rugby league football: A review

The purpose of this paper is to provide a comprehensive review of the science of rugby league football at all levels of competition (i.e. junior, amateur, semi-professional, professional), with special reference to all discipline-specific scientific research performed in rugby league (i.e. physiological, psychological, injury epidemiology, strength and conditioning, performance analysis). Rugby league football is played at junior and senior levels in several countries worldwide. A rugby league team consists of 13 players (6 forwards and 7 backs). The game is played over two 30?–?40 min halves (depending on the standard of competition) separated by a 10?min rest interval. Several studies have documented the physiological capacities and injury rates of rugby league players. More recently, studies have investigated the physiological demands of competition. Interestingly, the physiological capacities of players, the incidence of injury and the physiological demands of competition all increase as the playing standard is increased. Mean blood lactate concentrations of 5.2, 7.2 and 9.1?mmol?·?l^?1 have been reported during competition for amateur, semi-professional and professional rugby league players respectively. Mean heart rates of 152 beats?·?min^?1 (78% of maximal heart rate), 166 beats?·?min^?1 (84% of maximal heart rate) and 172 beats?·?min^?1 (93% of maximal heart rate) have been recorded for amateur, semi-professional and junior elite rugby league players respectively. Skill-based conditioning games have been used to develop the skill and fitness of rugby league players, with mean heart rate and blood lactate responses during these activities almost identical to those obtained during competition. In addition, recent studies have shown that most training injuries are sustained in traditional conditioning activities that involve no skill component (i.e. running without the ball), whereas the incidence of injuries while participating in skill-based conditioning games is low. Collaborative research among the various sport science disciplines is required to identify strategies to reduce the incidence of injury and enhance the performance of rugby league players. An understanding of the movement patterns and physiological demands of different positions at all standards of competition would allow the development of strength and conditioning programmes to meet the precise requirements of these positions. Finally, studies investigating the impact of improvements in physiological capacities (including the effect of different strength and conditioning programmes) on rugby league playing performance are warranted.     

Science of rugby league football: a review

The purpose of this paper is to provide a comprehensive review of the science of rugby league football at all levels of competition (i.e. junior, amateur, semi-professional, professional), with special reference to all discipline-specific scientific research performed in rugby league (i.e. physiological, psychological, injury epidemiology, strength and conditioning, performance analysis). Rugby league football is played at junior and senior levels in several countries worldwide. A rugby league team consists of 13 players (6 forwards and 7 backs). The game is played over two 30 - 40 min halves (depending on the standard of competition) separated by a 10 min rest interval. Several studies have documented the physiological capacities and injury rates of rugby league players. More recently, studies have investigated the physiological demands of competition. Interestingly, the physiological capacities of players, the incidence of injury and the physiological demands of competition all increase as the playing standard is increased. Mean blood lactate concentrations of 5.2, 7.2 and 9.1 mmol . l(-1) have been reported during competition for amateur, semi-professional and professional rugby league players respectively. Mean heart rates of 152 beats . min(-1) (78% of maximal heart rate), 166 beats . min(-1) (84% of maximal heart rate) and 172 beats . min(-1) (93% of maximal heart rate) have been recorded for amateur, semi-professional and junior elite rugby league players respectively. Skill-based conditioning games have been used to develop the skill and fitness of rugby league players, with mean heart rate and blood lactate responses during these activities almost identical to those obtained during competition. In addition, recent studies have shown that most training injuries are sustained in traditional conditioning activities that involve no skill component (i.e. running without the ball), whereas the incidence of injuries while participating in skill-based conditioning games is low. Collaborative research among the various sport science disciplines is required to identify strategies to reduce the incidence of injury and enhance the performance of rugby league players. An understanding of the movement patterns and physiological demands of different positions at all standards of competition would allow the development of strength and conditioning programmes to meet the precise requirements of these positions. Finally, studies investigating the impact of improvements in physiological capacities (including the effect of different strength and conditioning programmes) on rugby league playing performance are warranted.     

Game location and aggression in rugby league

The present study examined the relationship between aggression and game location in rugby league. We videotaped a random sample of 21 professional rugby league games played in the 2000 Super League season. Trained observers recorded the frequency of aggressive behaviours. Consistent with previous research, which used territoriality theories as a basis for prediction, we hypothesized that the home team would behave more aggressively than the away team. The results showed no significant difference in the frequency of aggressive behaviours exhibited by the home and away teams. However, the away teams engaged in substantially more aggressive behaviours in games they lost compared with games they won. No significant differences in the pattern of aggressive behaviours for home and away teams emerged as a function of game time (i.e. first or second half) or game situation (i.e. when teams were winning, losing or drawing). The findings suggest that while home and away teams do not display different levels of aggression, the cost of behaving aggressively (in terms of game outcome) may be greater for the away team.     

Game location and aggression in rugby league

The present study examined the relationship between aggression and game location in rugby league. We videotaped a random sample of 21 professional rugby league games played in the 2000 Super League season. Trained observers recorded the frequency of aggressive behaviours. Consistent with previous research, which used territoriality theories as a basis for prediction, we hypothesized that the home team would behave more aggressively than the away team. The results showed no significant difference in the frequency of aggressive behaviours exhibited by the home and away teams. However, the away teams engaged in substantially more aggressive behaviours in games they lost compared with games they won. No significant differences in the pattern of aggressive behaviours for home and away teams emerged as a function of game time (i.e. first or second half) or game situation (i.e. when teams were winning, losing or drawing). The findings suggest that while home and away teams do not display different levels of aggression, the cost of behaving aggressively (in terms of game outcome) may be greater for the away team.     

Groin injuries in professional rugby league players: a prospective study

Altogether, 100 uninjured professional rugby league players were evaluated over a 2-year period. Their height, body mass, sum of skinfolds, girths and bone diameters were recorded. A Cybex 340 isokinetic dynamometer was used to determine peak torque, work, power, endurance ratios and peak torque ratios of the hip abductors and adductors (5 repetitions at 0.52 and 2.08 rad. s(- 1); 20 repetitions at 3.66 rad. s(- 1)) and knee flexors and extensors (4 repetitions at 1.04 and 3.14 rad. s(- 1); 30 repetitions at 5.22 rad. s(- 1)). Hip abduction and adduction were also assessed with the hip in external rotation. Discriminant function analysis was conducted on all predictor variables to develop a multivariate predictive model capable of classifying players with a high degree of accuracy into groups with and without a groin injury. The model consisted of eight variables and correctly classified 91.7% of the non-injured players and 90.5% of the injured players. The correct classification for the model as a whole was 91.4%. The aetiological factors identified as being related to injury of the groin musculotendinous unit included abduction and adduction-with-rotation peak torque, angle of adduction and abduction-with-rotation peak torque, strength ratio of hip muscle groups, bilateral difference in extension peak torque, femur diameter and body mass.     

Groin injuries in professional rugby league players: a prospective study

Altogether, 100 uninjured professional rugby league players were evaluated over a 2-year period. Their height, body mass, sum of skinfolds, girths and bone diameters were recorded. A Cybex 340 isokinetic dynamometer was used to determine peak torque, work, power, endurance ratios and peak torque ratios of the hip abductors and adductors (5 repetitions at 0.52 and 2.08 rad?·?s^??1; 20 repetitions at 3.66 rad?·?s^??1) and knee flexors and extensors (4 repetitions at 1.04 and 3.14 rad?·?s^??1; 30 repetitions at 5.22 rad?·?s^??1). Hip abduction and adduction were also assessed with the hip in external rotation. Discriminant function analysis was conducted on all predictor variables to develop a multivariate predictive model capable of classifying players with a high degree of accuracy into groups with and without a groin injury. The model consisted of eight variables and correctly classified 91.7% of the non-injured players and 90.5% of the injured players. The correct classification for the model as a whole was 91.4%. The aetiological factors identified as being related to injury of the groin musculotendinous unit included abduction and adduction-with-rotation peak torque, angle of adduction and abduction-with-rotation peak torque, strength ratio of hip muscle groups, bilateral difference in extension peak torque, femur diameter and body mass.     

Peak movement and collision demands of professional rugby league competition

ABSTRACT

To quantify the peak movement and contact demands of National Rugby League (NRL) and European Super League (ESL) competition players were tracked during 10 NRL (166 files) and 10 ESL (143 files) matches using microtechnology devices. The peak 1- to 5-min periods were then calculated for average match speed (m·min^?1), and acceleration (m·s^?2) when 0, 1, 2, and ≥3 collisions per min occurred. Linear mixed effect models and Cohen’s effect size statistic (± 90%CI) were used to determine the differences in movement profiles when collisions occurred. Compared to no collision periods, as frequency of collisions per minute increased, there were progressive reductions in running speed for most positional groups. The addition of 1 or more collisions per min resulted in average effect size reductions in match speed of ?0.14 for NRL forwards, ?0.89 for NRL backs, ?0.48 for ESL forwards, and ?2.41 for ESL backs. ESL forwards had the highest frequency of peak periods involving 3 or more collisions per min, 22% of all periods, followed by NRL forwards (14%), NRL backs (10%) and ESL backs (8%). This study highlights the peak movement and collision demands of professional rugby league competition and allows practitioners to develop training drills that reflect worst case scenarios.     

An integrated analysis of match-related fatigue in professional rugby league

This study examined the changes in external outputs, including metabolic power variables, and internal response whilst considering contextual factors on physical performance variables during rugby league match play. Physical performance (total distance, high-speed running and high-power distances, average metabolic power), heart-rate (percentage heart-rate peak and training impulse), collisions (attacking and defensive) and contextual (time in attack, time in defence, time out of play) data were collected from 18 rugby league players during 38 games throughout two National Rugby League seasons. Physical variables were highest in the first 10-min period of each half (P < 0.001). Heart-rate indices peaked in the second 10-min period and were lower during second half periods (P < 0.001). Few differences existed in collisions and contextual factors across 10-min periods. Physical variables were highest during the first 5-min period compared to the final (P < 0.001). There was no difference in heart-rate response, attacking collisions or contextual factors between these periods. Following the peak 5-min period in the match, there were reductions in physical, heart-rate, defensive collisions and contextual factors (P < 0.001). The data show temporal changes in physical performance, heart-rate response and collisions during rugby league match play, although these are affected by contextual factors.     

Changes in locomotive rates during senior elite rugby league matches

The aim of this study was to quantify the changes in locomotive rates across the duration of senior elite rugby league matches. A semi-automated image recognition system (ProZone 3, ProZone?, Leeds, England) was used to track the movements of 59 players from six teams during three competitive matches. The players were classified into one of four positional groups: props (n = 9), back row (n = 9), pivots (n = 14) or outside backs (n = 27). Players' movements were classified as low, high or very high intensity running and reported as locomotive rates (distance covered per minute played) for successive quarters of each match. Analysis of variance revealed that only the outside backs showed a significantly lower overall locomotive rate during the final quarter compared to the first (P < 0.05). However, locomotive rates for high and very high intensity running during the final quarter were significantly lower (P < 0.05) than the first quarter among outside backs, pivots and props despite no change in the rate of involvements in contact. On the basis of these findings, it is suggested that high and very high intensity running locomotive rates may be more affective methods of detecting fatigue during competitive matches than overall locomotive rate.     

The expected value of possession in professional rugby league match-play

This study estimated the expected point value for starting possessions in different field locations during rugby league match-play and calculated the mean expected points for each subsequent play during the possession. It also examined the origin of tries scored according to the method of gaining possession. Play-by-play data were taken from all 768 regular-season National Rugby League (NRL) matches during 2010–2013. A probabilistic model estimated the expected point outcome based on the net difference in points scored by a team in possession in a given situation. An iterative method was used to approximate the value of each situation based on actual scoring outcomes. Possessions commencing close to the opposition’s goal-line had the highest expected point equity, which decreased as the location of the possession moved towards the team’s own goal-line. Possessions following an opposition error, penalty or goal-line dropout had the highest likelihood of a try being scored on the set subsequent to their occurrence. In contrast, possessions that follow an opposition completed set or a restart were least likely to result in a try. The expected point values framework from our model has applications for informing playing strategy and assessing individual and team performance in professional rugby league.     

Changes in locomotive rates during senior elite rugby league matches

Abstract

The aim of this study was to quantify the changes in locomotive rates across the duration of senior elite rugby league matches. A semi-automated image recognition system (ProZone 3, ProZone®, Leeds, England) was used to track the movements of 59 players from six teams during three competitive matches. The players were classified into one of four positional groups: props (n = 9), back row (n = 9), pivots (n = 14) or outside backs (n = 27). Players' movements were classified as low, high or very high intensity running and reported as locomotive rates (distance covered per minute played) for successive quarters of each match. Analysis of variance revealed that only the outside backs showed a significantly lower overall locomotive rate during the final quarter compared to the first (P < 0.05). However, locomotive rates for high and very high intensity running during the final quarter were significantly lower (P < 0.05) than the first quarter among outside backs, pivots and props despite no change in the rate of involvements in contact. On the basis of these findings, it is suggested that high and very high intensity running locomotive rates may be more affective methods of detecting fatigue during competitive matches than overall locomotive rate.     

Severity and cost of injuries in amateur rugby league: A case study

The aim of this study was to determine the severity and cost of injuries in amateur rugby league. Seventy-two amateur rugby league players aged 28 - 6 years (mean - s) were surveyed at the end of a competitive season. An injury was defined as any pain, disability or injury that occurred as a result of a competition game which caused the player to miss subsequent games. Injuries were classified as minor (one game missed), moderate (two to four games missed) and major (five or more games missed). Of the 72 questionnaires distributed, 34 (47.2%) were returned. Twenty respondents (58.8%) sustained an injury that resulted in one or more missed games. Eight injured players (40.0%) missed five or more training sessions, six of whom (30%) missed five or more games as a result of the injury. The median time lost from employment or study for all injured players was 2 days per playing injury. The respective median direct (e.g. medical expenses) and indirect (e.g. wages lost) costs associated with the injury were 28.29 and 77.04 per playing injury. A considerable proportion of injuries sustained in the present sample of amateur rugby league players were major, resulting in a loss of training, playing and employment or study time, and these injuries were associated with significant direct and indirect economic costs. Further studies, using a larger sample, would complement the present findings in establishing the severity and cost of amateur rugby league injuries. These results suggest that prevention strategies are required to reduce the severity and cost of amateur rugby league injuries.     

Influence of playing standard on the physical demands of professional rugby league

Abstract

In this paper we report on two studies that investigated the physical demands of professional rugby league match-play. Instudy one, National Rugby League (NRL) and National Youth Competition (NYC) players underwent global positioning system (GPS) analysis during competitive matches. No differences (P > 0.05) were observed between playing standards for minutes played, total distance covered, or the distances covered at low and high speeds. However, NRL players engaged in significantly more repeated high-intensity effort bouts than NYC players (13.1 ± 0.8 bouts vs. 9.7 ± 1.1 bouts). Reductions in physical performance occurred from the first to second half for both NRL and NYC players. In study two, we investigated, in the same players, the physical demands of professional rugby league match-play when players were competing in trial and regular fixture matches. The locomotor demands of trial matches were lower than fixture matches, with players covering less distance per minute of match-play, including less distance at low and high speeds. Players were also less likely to engage in repeated high-intensity effort bouts in trial matches than fixtures. These findings demonstrate that neither NYC matches nor NRL trial matches adequately reflect the intense physical demands of NRL fixture matches.     

Severity and cost of injuries in amateur rugby league: a case study

The aim of this study was to determine the severity and cost of injuries in amateur rugby league. Seventy-two amateur rugby league players aged 28 +/- 6 years (mean +/- s) were surveyed at the end of a competitive season. An injury was defined as any pain, disability or injury that occurred as a result of a competition game which caused the player to miss subsequent games. Injuries were classified as minor (one game missed), moderate (two to four games missed) and major (five or more games missed). Of the 72 questionnaires distributed, 34 (47.2%) were returned. Twenty respondents (58.8%) sustained an injury that resulted in one or more missed games. Eight injured players (40.0%) missed five or more training sessions, six of whom (30%) missed five or more games as a result of the injury. The median time lost from employment or study for all injured players was 2 days per playing injury. The respective median direct (e.g. medical expenses) and indirect (e.g. wages lost) costs associated with the injury were 28.29 pounds and 77.04 pound per playing injury. A considerable proportion of injuries sustained in the present sample of amateur rugby league players were major, resulting in a loss of training, playing and employment or study time, and these injuries were associated with significant direct and indirect economic costs. Further studies, using a larger sample, would complement the present findings in establishing the severity and cost of amateur rugby league injuries. These results suggest that prevention strategies are required to reduce the severity and cost of amateur rugby league injuries.     

Six-year body composition change in male elite senior rugby league players

This study investigated the change in body composition and bone mineral content (BMC) of senior rugby league (RL) players between 2008 and 2014. Twelve male professional RL players (age, 24.6 ± 4.0 years; stature, 183.4 ± 8.4 cm) received a dual-energy X-ray absorptiometry scan during preseason in 2008 and 2014. Between 2008 and 2014, very likely increases in leg lean mass (LM), total trunk and leg BMC, and a likely increase in arm BMC and possible increases in body mass (BM), total and trunk fat mass (FM), and total, trunk and arm LM were observed. Unlikely decreases and unclear changes in leg and arm FM were also found. Large negative correlations were observed between age and BM (r = ?0.72), LM (r = ?0.70), FM (r = ?0.61) and BMC (r = ?0.84) change. Three participants (19.1 ± 1.6 years) increased LM by 7.0–9.3 kg. Younger players had the largest increases in LM during this period, although an older player (30-year old) still increased LM. Differences in body composition change were also observed for participants of the same age, thus contextual factors should be considered. This study demonstrates the individuality of body composition changes in senior professional rugby players, while considering the potential change in young athletes.     

Influence of training and match intensity on injuries in rugby league

The aim of this study was to examine the influence of perceived intensity, duration and load of matches and training on the incidence of injury in rugby league players. The incidence of injury was prospectively studied in 79 semi-professional rugby league players during the 2001 season. All injuries sustained during matches and training sessions were recorded. Training sessions were conducted from December to September, with matches played from February to September. The intensity of individual training sessions and matches was estimated using a modified rating of perceived exertion scale. Training load was calculated by multiplying the training intensity by the duration of the training session. The match load was calculated by multiplying the match intensity by the time each player participated in the match. Training load increased from December (278.3 [95% confidence interval, CI 262.2 to 294.5] units) to February (385.5 [95% CI 362.4 to 408.5] units), followed by a decline until September (98.4 [95% CI 76.5 to 120.4] units). Match load increased from February (204.0 [95% CI 186.2 to 221.8] units) to September (356.8 [95% CI 302.5 to 411.1] units). More training injuries were sustained in the first half of the season (first vs second: 69.2% vs 30.8%, P?<0.001), whereas match injuries occurred more frequently in the latter stages of the season (53.6% vs 46.4%, P?<0.001). A significant relationship (P?<0.05) was observed between changes in training injury incidence and changes in training intensity (r?=?0.83), training duration (r?=?0.79) and training load (r?=?0.86). In addition, changes in the incidence of match injuries were significantly correlated (P?<0.05) with changes in match intensity (r?=?0.74), match duration (r?=?0.86) and match load (r?=?0.86). These findings suggest that as the intensity, duration and load of rugby league training sessions and matches is increased, the incidence of injury is also increased.     

Evidence of exercise-induced muscle damage following a simulated rugby league match

Abstract

This study investigated symptoms of exercise-induced muscle damage following a simulated rugby league game. Ten male participants were assessed before, immediately after (0 h), and 24 and 48 h after the simulated game. Perceived muscle soreness was higher at all time points (P=0.001) and creatine kinase values were increased at 24 h following the simulated game (P=0.001). Peak knee extensor torque at 60 deg · s^?1 was reduced up to 48 h (P =0.04) but was unchanged at 240 deg · s^?1. Similarly, peak knee flexor torque at 60 deg · s^?1 was lower than baseline up to 24 h, while at 240 deg · s^?1 it was reduced at 24 h only (P=0.045). Correlations between changes in strength loss of the knee extensors and fat mass to fat-free mass ratio reveleaved no significant relationship between variables (P >0.05). In addition, countermovement jump performance was reduced at 0 and 24 h following the simulated game (P=0.008). Our results suggest that symptoms of exercise-induced muscle damage occur up to 48 h following a simulated rugby league match. Coaches should be cognisant of the large increases in muscle soreness and reductions in slow velocity force generation, and should adapt training accordingly in the 48 h period following a game.     

Influence of training and match intensity on injuries in rugby league

The aim of this study was to examine the influence of perceived intensity, duration and load of matches and training on the incidence of injury in rugby league players. The incidence of injury was prospectively studied in 79 semi-professional rugby league players during the 2001 season. All injuries sustained during matches and training sessions were recorded. Training sessions were conducted from December to September, with matches played from February to September. The intensity of individual training sessions and matches was estimated using a modified rating of perceived exertion scale. Training load was calculated by multiplying the training intensity by the duration of the training session. The match load was calculated by multiplying the match intensity by the time each player participated in the match. Training load increased from December (278.3 [95% confidence interval, CI 262.2 to 294.5] units) to February (385.5 [95% CI 362.4 to 408.5] units), followed by a decline until September (98.4 [95% CI 76.5 to 120.4] units). Match load increased from February (204.0 [95% CI 186.2 to 221.8] units) to September (356.8 [95% CI 302.5 to 411.1] units). More training injuries were sustained in the first half of the season (first vs second: 69.2% vs 30.8%, P < 0.001), whereas match injuries occurred more frequently in the latter stages of the season (53.6% vs 46.4%, P < 0.001). A significant relationship (P < 0.05) was observed between changes in training injury incidence and changes in training intensity (r = 0.83), training duration (r = 0.79) and training load (r = 0.86). In addition, changes in the incidence of match injuries were significantly correlated (P < 0.05) with changes in match intensity (r = 0.74), match duration (r = 0.86) and match load (r = 0.86). These findings suggest that as the intensity, duration and load of rugby league training sessions and matches is increased, the incidence of injury is also increased.