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Factors affecting exercise intensity in professional rugby league match-play

      Abstract

      Objectives

      To examine the effects of match-related and individual player characteristics on running performance in professional rugby league matches.

      Design

      Longitudinal observational study.

      Methods

      Global positioning system (GPS) and technical performance measures (attacking involvements and tackles made) were collected from 23 players competing in the National Rugby League (NRL) over 24 matches during a season. The GPS data were categorised into relative total distance (m min−1) and relative high-speed running distance (HSR m min−1, >14.4 km h−1). Each match was classified according to season phase, location, recovery length, opposition strength and result. Individual player fitness status was obtained from a 1.2-km shuttle run test conducted prior to the start of the season. Two separate linear mixed models were constructed to examine the influence of match-related and individual player characteristics on relative total and HSR distances.

      Results

      Matches played away from home, early in the season and following short recovery cycles were associated with reduced relative total and HSR distances. Matches won contained less relative total and HSR distance; whereas only HSR distance was higher against weaker opposition. The total time the ball was out of play reduced relative total but not HSR distances. The number of defensive but not attacking involvements influenced both physical performance measures. Finally, player fitness was positively related to both relative total and HSR distances.

      Conclusions

      There appears to be a complex interplay of factors affecting match-running performance in rugby league. The results underline the importance of considering contextual factors when analysing rugby league match-activity profiles.

      Keywords

      1. Introduction

      Time motion analyses of competition matches – using either global positioning satellite (GPS) or video tracking technology – are now common for assessing time–motion profiles in rugby league
      • Gabbett T.
      • Jenkins D.
      • Abernethy B.
      Physical demands of professional rugby league training and competition using microtechnology.
      • Kempton T.
      • Sirotic A.C.
      • Rampinini E.
      • et al.
      Metabolic power demands of rugby league match-play.
      and other professional team sports.
      • Coutts A.J.
      • Quinn J.
      • Hocking J.
      • et al.
      Match running demands of elite Australian rules football.
      • Rampinini E.
      • Coutts A.
      • Castagna C.
      • et al.
      Variation in top level soccer match performance.
      Recent research has demonstrated that physical performance variables (particularly higher-speed activities) vary between individuals and throughout the course of the season.
      • Kempton T.
      • Sirotic A.
      • Coutts A.J.
      Between match variation in professional rugby league competition.
      • Kempton T.
      • Sullivan C.
      • Bilsborough J.
      • et al.
      Match-to-match variation in physical activity and technical skill measures in professional Australian football.
      Indeed, given the complex nature of team sport match-play, it is likely that a variety of situational factors including opposition strength, match outcome and competition scheduling contribute to the variation in physical activity profiles.
      • Gabbett T.
      Influence of the opposing team on physical performance in elite rugby league match-play.
      • Murray N.B.
      • Gabbett T.J.
      • Chamari K.
      Effect of different between-match recovery times on the activity profiles and injury rates of national rugby league players.
      Additionally, individual player characteristics such as playing position and fitness characteristics may also influence physical performance profiles.
      • Kempton T.
      • Sirotic A.C.
      • Rampinini E.
      • et al.
      Metabolic power demands of rugby league match-play.
      • Gabbett T.J.
      • Stein J.
      • Kemp J.
      • et al.
      Relationship between tests of physical qualities and physical match performance in elite rugby league players.
      Recently, several studies examined the influence of these match-related factors and individual specific qualities on physical activity profiles during rugby league match-play.
      • Gabbett T.
      Influence of the opposing team on physical performance in elite rugby league match-play.
      • Murray N.B.
      • Gabbett T.J.
      • Chamari K.
      Effect of different between-match recovery times on the activity profiles and injury rates of national rugby league players.
      • Gabbett T.J.
      • Stein J.
      • Kemp J.
      • et al.
      Relationship between tests of physical qualities and physical match performance in elite rugby league players.
      While these studies have expanded current knowledge of rugby league match-play, they are often limited in that they only examined these variables in isolation and have not adequately controlled for the confounding effects of multiple match-related factors on physical activity profiles. Additional research is therefore required to better understand the independent effects of these situational variables on physical activity profiles. Multilevel mixed modelling represents a method to examine the independent effects of a variable on an outcome variable whilst accounting for all other variables. Additionally, this technique allows for the analysis of clustered dependent data as is commonly collected in observational match-analysis studies. Therefore, the purpose of this study was to use a mixed models approach to examine the independent effects of match location, season phase, recovery length, opposition strength, match outcome, time out of play, player involvements and player fitness status on both total and high-speed relative distance during professional rugby league match-play. These factors were selected for analysis based on findings from previous research in rugby league
      • Gabbett T.
      Influence of the opposing team on physical performance in elite rugby league match-play.
      • Murray N.B.
      • Gabbett T.J.
      • Chamari K.
      Effect of different between-match recovery times on the activity profiles and injury rates of national rugby league players.
      and other team sports.
      • Helgerud J.
      • Engen L.
      • Wisloff U.
      • et al.
      Aerobic endurance training improves soccer performance.
      • Mooney M.
      • O’Brien B.
      • Cormack S.
      • et al.
      The relationship between physical capacity and match performance in elite Australian football: a mediation approach.
      • Lago C.
      • Casais L.
      • Dominguez E.
      • et al.
      The effects of situational variables on distance covered at various speeds in elite soccer.
      An improved understanding of the influence of these factors on measures of physical performance is important to enhance the interpretation of time–motion analyses and assist teams in preparing for rugby league match-play.

      2. Methods

      Data were collected from a cohort of 23 rugby league players (age: 25.5 ± 3.7 y; mass: 97.7 ± 11.1 kg; stature: 1.83 ± 0.06 m) from the same club during 24 games (15 wins and 9 losses) throughout the Australian National Rugby League (NRL) competition season. Matches were played in outdoor stadiums on quality natural grass fields in a variety of weather conditions. The observational group contained 6 pivots, 7 outside backs, 5 wide-running forwards and 5 hit-up forwards.
      • Gabbett T.
      • Jenkins D.
      • Abernethy B.
      Physical demands of professional rugby league training and competition using microtechnology.
      A total of 352 (pivots = 90; outside backs = 91; wide-running forwards = 86; hit-up forwards = 85) complete match samples were obtained for analysis. The mean (±SD) number of observations for each player was 15 ± 6 (range 6–23). Informed consent and institutional ethics approval were obtained (HREC: 2012000260).
      Each match was classified according to season phase (early season, matches 1–8; mid-season, matches 9–16; or late season, matches 17–24), location (home or away), recovery length (5–6 or ≥7 days between matches), opposition strength (top five, middle five or bottom five according to final ladder position) and result (won or lost). The mean (±SD) match-day temperature for the three phases of the season were 26.0 ± 2.9, 18.0 ± 1.9 and 16.9 ± 2.8 °C, respectively. The total attacking involvements (i.e. gaining possession of the ball when in attack) and tackles completed by each player, as well as the total amount of time in which the ball was out of play during each match was obtained from a commercial statistics provider (Prozone, Sydney, Australia). Individual player aerobic fitness status was obtained from a 1.2-km shuttle run test, which is highly correlated with other field tests of aerobic capacity in team sport athletes.
      • Kelly V.G.
      • Wood A.
      The correlation between the 30–15 intermittent fitness test and a novel test of running performance.
      The test involved continuous return shuttle running over 20 m, 40 m and 60 m intervals, with this sequence repeated five times to achieve a total distance of 1.2 km during the test. The time to complete the test was recorded with a stop watch and used to calculate the maximal running speed (MRS; m s−1).
      • Kelly V.G.
      • Wood A.
      The correlation between the 30–15 intermittent fitness test and a novel test of running performance.
      The 1.2 km shuttle run test was conducted on a quality natural grass playing surface during pre-season training prior to the start of the competition season.
      Player movements during games were measured using GPS units which supplement 5 Hz GPS sampling rate data by interpolating GPS bearing data at 10 Hz (SPI-Pro X, GPSports, Canberra, Australia). The units were placed into a customised pouch in the jersey located between the scapulae of the player. The SPI-Pro X devices provide acceptable validity and reliability for measuring movements over long distances at low speeds, however, they are less precise when assessing short, high speed activities.
      • Johnston R.
      • Watsford M.
      • Kelly S.
      • et al.
      Validity and interunit reliability of 10 Hz and 15 Hz GPS units for assessing athlete movement demands.
      Each player wore the same GPS unit for each match during the season to minimise inter-unit error. Following each match, the GPS data were analysed using the TeamAMS proprietary software (version R1.2013.18). The match files were cleaned so that only data recorded when the player was on the field was retained for further analysis. The total and high-speed running distances (HSR; >14.4 km h−1) were divided by total playing time to obtain the relative total (m min−1) and high-speed distances (HSR m min−1), respectively.
      • Abt G.
      • Lovell R.
      The use of individualised speed and intensity thresholds for determining the distance run at high-intensity in professional soccer.
      A 3-level linear mixed model was used to examine the effects of match and player characteristics on relative distances covered during match-play (Table 1). The study design located units of analysis (individual player match sample) nested in clusters of units (player), which were nested in larger clusters of clusters (position group). Linear mixed models may involve both fixed effects (which describe the relationship between the dependent variable and covariates for an entire population) and random effects (which are associated with a random factor and usually represent random deviations from relationships described by fixed effects). Random effects can exist as either random intercepts or random coefficients in a linear mixed model.
      • West B.T.
      • Welch K.B.
      • Galecki A.T.
      Linear mixed models: a practical guide using statistical software.
      Two separate linear mixed models were constructed to examine the influence of various level 1 and 2 covariates on relative total (Model 1) and HSR (Model 2) distances during match-play. The relative total and HSR distances were log transformed prior to analysis to provide differences as a percentage of the mean.
      • Hopkins W.
      • Marshall S.
      • Batterham A.
      • et al.
      Progressive statistics for studies in sports medicine and exercise science.
      Random factors were included in the model to investigate deviations for players and position groups from the overall fixed intercept and fixed coefficients.
      Table 1Covariates included in model specification.
      Level of DataFactorsTypeClassification
      Level 3Cluster of clusters (random factor)Position
      Level 2Cluster of units (random factor)Player
      CovariateFitness scoreContinuous
      Grand mean centred variable.
      Maximal running speed (m s
      • Gabbett T.
      • Jenkins D.
      • Abernethy B.
      Physical demands of professional rugby league training and competition using microtechnology.
      )
      Level 1Unit of analysisIndividual match sample
      Dependent variableRelative total distance (Model 1)Continuousm min−1
      Relative high-speed distance (Model 2)Continuousm min−1
      CovariatesLocationDummy variable0 = Home, 1 = Away
      Recovery lengthDummy variable0 = Standard, 1 = Short
      Season phaseDummy variableEarly, middle or late season
      Opposition strengthDummy variableTop, middle or bottom ranked
      ResultDummy variable0 = Loss, 1 = Win
      Time out of playContinuous
      Grand mean centred variable.
      Time that ball was out of play (mins)
      PossessionsContinuousNumber of possessions
      TacklesContinuousNumber of tackles made
      * Grand mean centred variable.
      A ‘step-up’ model construction strategy was employed, beginning with an “unconditional” model containing only a fixed intercept and level 2 and 3 random factors.
      • West B.T.
      • Welch K.B.
      • Galecki A.T.
      Linear mixed models: a practical guide using statistical software.
      The model was then developed by adding each single level 1 fixed effect, followed by level 2 fixed effects. Each single fixed effect was retained if it demonstrated statistical significance (p < 0.05) and improved the model information criteria compared to the previous model as determined by a likelihood ratio test. Level 1 and 2 fixed effects were also tested for random coefficient effects by comparing a model containing the random effect to that containing the fixed effect for each covariate. Both time out of play and fitness score were grand-mean centred. The intra-class correlation coefficient (ICC) was used to determine the similarity of observed responses within both the positional and individual player clusters. The t statistics from the mixed models were converted to effect size (ES) correlations and associated 90% CI.
      • Rosnow R.L.
      • Rosenthal R.
      • Rubin D.B.
      Contrasts and correlations in effect-size estimation.
      Effect sizes were interpreted as <0.1, trivial; 0.1–0.3, small; 0.3–0.5, moderate; 0.5–0.7, large; 0.7–0.9, very large; 0.9–0.99, almost perfect; 1.0, perfect.
      • Hopkins W.
      • Marshall S.
      • Batterham A.
      • et al.
      Progressive statistics for studies in sports medicine and exercise science.
      All statistical analyses were conducted using the lme4 and psychometric packages in R statistical software (R.3.1.0, R Foundation for Statistical Computing).

      3. Results

      For both model 1 and 2, the construction process was optimised by including random intercept effects, demonstrating that there was statistically significant variance in both mean relative total and HSR distances between individual players nested in positions. Level one covariates location (away), season phase (early) and recovery length (short) all reduced both relative total and HSR distances (Table 2). There was a small to moderate reduction in relative total and HSR distances for matches won, although there was a small to moderate increase in HSR distance only against weaker opponents. In contrast, greater time that the ball is out of play during the match resulted in a small to moderate decrement in relative total distance but not relative HSR distance. An increase in tackles made by an individual player was associated with a trivial to small reductions in relative total and HSR distances, while the number of individual attacking involvements had no effect. Aerobic fitness (MRS) had a moderate to large positive effect on both relative total and HSR distances. The random intercept effects for relative total distance (Model 1) were 2.2%, −2.9%, −0.9%, 1.7% and for pivots, outside backs, wide-running forwards and hit-up forwards, respectively. There were no random effects for relative HSR distance for playing position (Model 2). There were no random coefficient effects for any level one covariate in either model, indicating that these effects were consistent across individual players and positional groups.
      Table 2Percentage effects of covariates on log transformed relative total and HSR distance in professional rugby league match-play (90% CI).
      Total distance (Model 1)HSR distance (Model 2)
      Coefficient90% CIdft ValueEffect sizeCoefficient90% CIdft ValueEffect size
      Fixed effects
      Intercept (m min−1)
      Exponential of intercept.
      89.086.0, 92.17.7215.716.315.0, 17.9116.151.9
      Location−4.1−5.2, −3.0325.9−5.90.31 (0.23–0.39)−17.2−21.0, −13.3328.5−6.70.35 (0.27–0.42)
      Early−4.8−5.9, −3.7338.8−7.00.36 (0.28–0.43)−17.9−21.5, −14.1340.2−7.10.36 (0.28–0.43)
      Short−1.7−3.0, −0.4325.6−2.10.12 (0.03–0.21)−5.9−10.5, −1.0326.7−2.00.11 (0.02–0.20)
      Result−1.7−2.8, −0.5326.5−2.30.13 (0.04–0.22)−11.4−15.6, −7.0327.9−4.10.22 (0.13–0.30)
      BottomNS13.48.6, 18.4326.24.70.25 (0.17−0.33)
      Time out of play (min)−0.4−0.5, −0.3326.7−6.00.32 (0.24–0.40)NS
      Fitness (m s−1)10.83.6, 18.517.92.50.51 (0.44−0.57)56.726.3, 94.519.73.40.61 (0.55–0.66)
      Tackles (n)−0.1−0.2, 0.0248.2−2.00.13 (0.04–0.22)−0.4−0.7, −0.2163.6−2.60.20 (0.11–0.28)
      CI: confidence interval; df: degrees of freedom; NS: covariate non-significant in final model.
      Exponential of intercept.
      The covariance parameters for relative total distance (Model 1) were 0.000791, 0.001351, 0.002854 and for relative HSR distance (Model 2) 0.0, 0.01423, 0.04034 for position-level, athlete-level and the residual, respectively. The ICC for individual match samples within each position cluster was 0.08 and 0.00 for relative total and HSR distances, respectively. While for individual match samples within each individual player the ICC was 0.36 and 0.32 for relative total and HSR distances, respectively. Observations of match samples within each position were only slightly correlated, while there was a higher correlation between match samples within each individual player.

      4. Discussion

      This study used a mixed models approach to examine the independent effects of various match-related and individual player factors on both relative total and high-speed distances during professional rugby league match-play. We found that matches played away from home, early in the season and following short recovery cycles were all associated with reduced relative total and HSR distances. In contrast, matches won contained less relative total and HSR distance; whereas only HSR distance was higher against weaker opposition. The total time the ball was out of play reduced relative total but not HSR distances. The number of defensive but not attacking involvements reduced both relative total and HSR distance. Finally, player fitness was positively related to both relative total and HSR distances. These findings have important implications for enhancing the interpretation of physical performance analyses and assisting teams in preparing for rugby league match-play.
      There was a trivial to small effect of match outcome on both the relative total and HSR distances, which were lower in matches won compared to matches lost. This finding is in direct contrast to previous research in professional rugby league, which reported higher relative total distances and no difference in HSR distances between winning and losing teams.
      • Gabbett T.
      Influence of the opposing team on physical performance in elite rugby league match-play.
      The author of that study concluded that the ability to perform greater amounts of low-speed activity between bouts of higher-speed activities differentiate between winning and losing teams.
      • Gabbett T.
      Influence of the opposing team on physical performance in elite rugby league match-play.
      Our results question whether higher relative total and HSR distances differentiate between winning and losing matches. Indeed, our results relate well to recent research from other football codes including soccer
      • Rampinini E.
      • Coutts A.
      • Castagna C.
      • et al.
      Variation in top level soccer match performance.
      • Di Salvo V.
      • Gregson W.
      • Atkinson G.
      • et al.
      Analysis of high intensity activity in premier league soccer.
      and Australian Football
      • Sullivan C.
      • Bilsborough J.
      • Hocking J.
      • et al.
      Match score affects activity profile and skill performance in professional Australian football players.
      which have reported lower running demands in matches won. However, a limitation of the present study is that we did not consider the margin of the result in the analysis, whereas previous research in other football codes has demonstrated the large margins are associated with lower physical activity measures.
      • Sullivan C.
      • Bilsborough J.
      • Hocking J.
      • et al.
      Match score affects activity profile and skill performance in professional Australian football players.
      Nonetheless, the lack of agreement between the present study and previous research in rugby league may also be due to differences in playing style and tactics of the observed team.
      • Gabbett T.
      Influence of the opposing team on physical performance in elite rugby league match-play.
      Moreover, the strength of the opposition was not accounted for in that previous study which may have confounded their results.
      • Gabbett T.
      Influence of the opposing team on physical performance in elite rugby league match-play.
      In the present study we have controlled for the strength of opposition which permits investigation of the independent effects of match outcome. Indeed, we found that there was no difference in relative total distance according to opponent strength, although there was a small to moderate increase in HSR distances against weaker opponents. While we have classified opposition strength based on their final finishing position, this method is unable to account for short term fluctuations in form which may have affected the present results. Future studies should consider the influence of score margin and opposition recent form on physical activity profiles in rugby league.
      This study was the first to examine the influence of match location on physical demands in rugby league match-play. There was a small to moderate increase in both relative total and HSR distances in home matches, which is in line with previous research from professional soccer.
      • Lago C.
      • Casais L.
      • Dominguez E.
      • et al.
      The effects of situational variables on distance covered at various speeds in elite soccer.
      The ‘home advantage’ has been well established in many professional sporting competitions, and may contribute to the increased running performance observed in the present study. Potential mechanisms underpinning the ‘home advantage’ include crowd influence, travel effects, as well as familiarity and territoriality associated with playing at the home stadium.
      • Pollard R.
      • Pollard G.
      Long-term trends in home advantage in professional team sports in North America and England (1876–2003).
      In the early phase of the season (i.e. the first eight games), there was a small to moderate reduction in relative total and HSR distances compared to the middle and late stages of the season. Similar findings have been reported in both soccer
      • Rampinini E.
      • Coutts A.
      • Castagna C.
      • et al.
      Variation in top level soccer match performance.
      and Australian Football,
      • Kempton T.
      • Sullivan C.
      • Bilsborough J.
      • et al.
      Match-to-match variation in physical activity and technical skill measures in professional Australian football.
      and it has been suggested that improved fitness and specific adaptations to match-play may explain increased physical profiles observed during the later stages of the competition season.
      • Rampinini E.
      • Coutts A.
      • Castagna C.
      • et al.
      Variation in top level soccer match performance.
      Another potential explanation for the lower relative distances observed during the first eight games of the season may relate to environmental factors. Specifically, the mean match-day temperatures in the first phase of the season (commencing early autumn) were higher compared to the latter stages of the competition. Indeed, reductions in match-running performance in team sport athletes have been previously reported during matches played in warm conditions, potentially due to increased fatigue
      • Mohr M.
      • Mujika I.
      • Santisteban J.
      • et al.
      Examination of fatigue development in elite soccer in a hot environment: a multi-experimental approach.
      or the adoption of deliberate pacing strategies.
      • Duffield R.
      • Coutts A.
      • Quinn J.
      Core temperature responses and match running performance during intermittent-sprint exercise competition in warm conditions.
      There was a trivial to small reduction in both relative total and HSR distance in games with a short (5–6 days) between-match recovery cycle. This decrement may be attributable to residual neuromuscular and perceptual fatigue and muscle damage arising from the previous match.
      • McLean B.
      • Coutts A.
      • Kelly V.
      • et al.
      Neuromuscular, endocrine, and perceptual fatigue responses during different length between match microcycles in professional rugby league players.
      While most physiological recovery markers have been shown to recover to pre-match levels within 4 days following a match, it is possible that reducing training loads to facilitate recovery during a short recovery cycle may effect preparation for the subsequent match.
      • McLean B.
      • Coutts A.
      • Kelly V.
      • et al.
      Neuromuscular, endocrine, and perceptual fatigue responses during different length between match microcycles in professional rugby league players.
      Our findings are in contrast to previous reports from NRL competition where higher relative distances were observed in matches following a short turn-around, although that study did report a reduced occurrence of repeated high-intensity efforts.
      • Murray N.B.
      • Gabbett T.J.
      • Chamari K.
      Effect of different between-match recovery times on the activity profiles and injury rates of national rugby league players.
      The disaccord between this previous study and the present findings could be due to the failure to account for contextual factors such as time out of play, or may alternatively be attributable to differences in the recovery strategies and training schedules between the reference teams. Collectively, our results suggest that recovery strategies and training schedules should be carefully planned during short match recovery cycles to preserve running performance during subsequent matches.
      Increases in the total time in which the ball was out of play resulted in a small to moderate reduction in the relative total distance during match-play. Our findings support previous research in both rugby league
      • Kempton T.
      • Sirotic A.
      • Cameron M.
      • et al.
      Match-related fatigue reduces physical and technical performance during elite rugby league match-play: a case study.
      and soccer
      • Carling C.
      Interpreting physical performance in professional soccer match-play: should we be more pragmatic in our approach?.
      which has shown that the amount of time that the ball is out of play need be considered when analysing match-activity profiles as it may reduce exercise intensities. Interestingly, relative HSR distance was not affected by time out of play, suggesting that these higher-speed activities are maintained during match-play, whereas stoppages have a larger influence on low-speed activities as most of the distance completed in these periods is of lower intensity.
      The complex relationships between physical and technical/tactical components have been suggested as important determinants of match performance in team sports, and thorough match analyses should not consider these dimensions in isolation.
      • Impellizzeri F.
      • Marcora S.
      Test validation in sport physiology: lessons learned from clinimetrics.
      Accordingly, we examined the association between attacking and defensive involvements and relative total and HSR distances. While, there was no effect of attacking involvements, the number of tackles completed resulted in a trivial to small reduction in both relative total and HSR distances. Indeed, tackles contribute significantly to physical demands of rugby league match-play,
      • Gabbett T.
      • Jenkins D.
      • Abernethy B.
      Physical demands of professional rugby league training and competition using microtechnology.
      and the fatigue arising from these game-specific actions likely reduces subsequent running activities.
      • Johnston R.
      • Gabbett T.
      • Seibold A.
      • et al.
      Influence of physical contact on pacing strategies during game-based activities.
      Taken together, these findings show the importance of developing collision specific fitness characteristics to attenuate the reduction in match running profiles arising from defensive involvements.
      Fitness characteristics are considered important determinants of physical performance in team sports.
      • Impellizzeri F.
      • Marcora S.
      Test validation in sport physiology: lessons learned from clinimetrics.
      We observed that higher aerobic fitness (as determined by the 1.2 km shuttle test) were associated with moderate to large increases in relative total and HSR distances. Similar relationships between physical capacity and match running performance have been reported for Australian Football
      • Mooney M.
      • O’Brien B.
      • Cormack S.
      • et al.
      The relationship between physical capacity and match performance in elite Australian football: a mediation approach.
      and soccer.
      • Castagna C.
      • Impellizzeri F.
      • Cecchini E.
      • et al.
      Effects of intermittent-endurance fitness on match performance in young male soccer players.
      Furthermore, it has been shown that improving physical capacity leads to elevated match running performance in team sport athletes.
      • Helgerud J.
      • Engen L.
      • Wisloff U.
      • et al.
      Aerobic endurance training improves soccer performance.
      In contrast, previous research in rugby league has reported mixed results, with some but not all physical fitness qualities relating to match running performance.
      • Gabbett T.J.
      • Stein J.
      • Kemp J.
      • et al.
      Relationship between tests of physical qualities and physical match performance in elite rugby league players.
      Caution is required when comparing our findings with previous rugby league research due to different physical capacity tests employed in the respective studies. Additionally, this previous research did not account for the influence of playing position on the relationship between physical capacity and match physical performance.
      • Gabbett T.J.
      • Stein J.
      • Kemp J.
      • et al.
      Relationship between tests of physical qualities and physical match performance in elite rugby league players.
      Collectively, our results suggest that higher aerobic fitness is associated with elevated physical performance during matches, and as such the development of these qualities are an important consideration in the preparation of professional rugby league athletes. Future studies should consider the relationship between additional tests of various fitness qualities and match running performance in order to establish the construct validity of these tests.
      • Impellizzeri F.
      • Marcora S.
      Test validation in sport physiology: lessons learned from clinimetrics.

      5. Conclusion

      This study examined the effects of match-related factors and individual characteristics on running performance in professional rugby league. The results underline the importance of considering contextual factors when analysing match activity profiles from competition play. There appears to be a complex interplay of factors affecting match-running performance in team sports such as rugby league, and multilevel mixed models are a statistical approach which permits analysis of the independent effects of such factors.

      6. Practical applications

      • Pre-season training programs should focus on improving aerobic fitness characteristics as this is associated with greater match-running performance.
      • Specific contact-based conditioning activities are required to attenuate the reduction in match running profiles arising from the physical demands of defensive collisions.
      • Recovery strategies and training schedules should be carefully planned during short between match recovery cycles to preserve running performance during subsequent matches.

      Acknowledgements

      No external sources of funding were provided for this study.

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