Rugby league is a collision sport played throughout several countries worldwide. The game is physically demanding, requiring players to perform bouts of high-intensity exercise (e.g., sprinting and tackling) separated by periods of low-intensity activity (e.g., standing, walking, and jogging) (5). Given the intense physical demands of the game, time-motion analysis is of importance to applied sport scientists and strength and conditioning staff to assist in the development of game-specific conditioning programs.
Several researchers have investigated the activity profiles of rugby league match-play using both video-based time-motion analysis (2,21,24) and microtechology (i.e., global positioning systems [GPS], accelerometers, and gyroscopes) devices (11,28). Professional rugby league players have been reported to cover approximately 90–100 m·min−1 (8,9,11,25,28,29) with 6–14 m·min−1 covered in high-speed running activities (11,29). Repeated high-intensity effort (RHIE) bouts (defined as 3 or more high acceleration, high speed, or contact efforts with <21 seconds between efforts) have also been shown to occur regularly, with players performing 1 RHIE bout every 6.9 minutes (11). Hit-up forwards (i.e., props) perform these activities more frequently (1 every 4.8 minutes) than the wide-running forwards (i.e., second rowers and locks) (1 every 6.3 minutes), adjustables (i.e., hookers, halfbacks, five-eighths, and fullbacks) (1 every 7.7 minutes), and outside backs (i.e., centers and wingers) (1 every 9.1 minutes) positional groups (11). The fatiguing nature of RHIE bouts (17), coupled with their relationship with tries scored and conceded (2), suggests that the ability (or inability) to perform these activities could prove critical to the outcome of the game (8).
Recently, the activity cycles (i.e., ball-in-play) of National Rugby League matches were investigated (6,7). The average longest ball-in-play period was 318 seconds, and the longest ball-in-play period from any match was approximately 11 minutes (6). Of interest was the finding that across an 80 minute game, the ball was in play for an average of 55 minutes, demonstrating that over 30% of match time comprises stoppages (i.e., for scrums, penalties, line drop-outs, tries, and video referee decisions). To date, most, but not all (12), investigations of the activity profiles of rugby league match-play have reported the physical demands across the 80 minutes match, irrespective of stoppages in play. Consequently, the reported demands of rugby league competition which include these stoppages, are likely to severely underestimate the “active” demands of match-play. In addition, given that most sport scientists analyze training activities on a “drill-by-drill” basis and exclude inactive training time (e.g., coach instruction, drinks breaks) (22), any comparison of training and competition demands would result in an artificial increase of training intensity relative to match-play. As such, conditioning programs based on match-play demands that include both active and inactive playing time could result in players being underprepared for the most demanding passages of play. Given the role of strength and conditioning coaches is to prepare players for the physical demands of competition, including the most demanding passages of play, then an understanding of the active demands of match-play is necessary. With this in mind, the purpose of this study was to investigate the activity profiles of rugby league match-play, accounting for ball “in” and “out-of-play” periods. It was anticipated that analysis of microtechnology data relative to ball-in-play time would provide a more accurate reflection of the physical demands placed on players during active rugby league match-play.
Experimental Approach to the Problem
The activity cycles of semiprofessional rugby league matches were investigated using a prospective cohort experimental design. Matches played through the 2012 season were coded for activity and recovery cycles. Time when the ball was continuously in play was considered activity, whereas any stoppages during the match (e.g., for scrums, penalties, line drop-outs, tries, and video referee decisions) were considered recovery. The activity profiles of players were also recorded using GPS devices. It was hypothesized that meaningful differences would exist between ball “in” and “out-of-play” for the match activity profiles and that matches with longer ball-in-play periods would be negatively associated with relative match intensity.
One-hundred four male rugby league players (mean age, 24.0 ± 3.0 years) from 11 teams competing in the Queensland Cup rugby league competition participated in this study. All participants received a clear explanation of the study, including information on the risks and benefits, and written consent was obtained. All experimental procedures were approved by the Institutional Review Board for Human Investigation.
Global positioning system analysis was completed during 22 matches (totaling 199 appearances). Movement was recorded by a minimaxX GPS unit (Catapult Innovations, Melbourne, Australia) sampling at 10 Hz. The GPS signal provided information on speed, distance, position, and acceleration. The GPS unit also included triaxial accelerometers and gyroscopes sampling at 100 Hz to provide information on physical collisions and RHIEs. The unit was worn in a small vest on the upper back of the players.
All GPS files were recorded in “real-time” using a wireless receiver and manufacturer provided software (Sprint, version 5; Catapult Sports, Victoria, Australia). Matches were coded for activity and recovery cycles. Time when the ball was continuously in play was considered activity, whereas any stoppages during the match (e.g., for scrums, penalties, line drop-outs, and tries) were considered recovery.
Data were categorized into (a) low (0–5 m·second−1) and high (>5 m·second−1) movement speed bands (8); (b) collisions; and (c) RHIE. A RHIE bout was defined as 3 or more high acceleration (≥2.79 m·second−2) (1), high speed, or contact efforts with less than 21 seconds recovery between efforts (11). The 10-Hz minimaxX units have been shown to have acceptable validity for measuring total distance (SE of the estimate = 3.8%) (16). Acceptable reliability has also been reported for total distance covered (intraclass correlation coefficient = 0.69, typical error of measurement = 2.0%), and distances covered at low speed (intraclass correlation coefficient = 0.68, typical error of measurement = 4.3%), and high speed (intraclass correlation coefficient = 0.86, typical error of measurement = 7.9%) (20). The minimaxX units have been shown to have acceptable validity and reliability for measuring high speed (bias = −0.2%; coefficient of variation = 2.0%) and acceleration (bias = −2.1%; coefficient of variation = 1.9%) efforts (27). In addition, the minimaxX units have been shown to offer a valid measurement of the collisions that commonly occur in rugby league, with the standard error of the estimate between collisions recorded by the minimaxX units and those coded from video recordings of the actual collision events reported to be 4.7% (4). The intraclass correlation coefficient for test-retest reliability and coefficient of variation for the detection of collisions were 0.95 and 3.0%, respectively. Finally, the validity of the minimaxX units to quantify RHIE was determined by having players perform 2 to 4 bouts of 6 tackles, with each tackle separated by ∼10 seconds of low-intensity activity. The SE of the estimate between RHIEs recorded by the minimaxX units and those coded from video recordings of the actual RHIE bout was 5.6% (8).
Differences in activity profiles between ball-in-play and full match data were compared using statistical significance testing and by using a practical approach based on the real-world relevance of the results (15). First, differences in the physical demands (i.e., distance covered at low and high speeds, collisions, and RHIE activity) between ball-in-play and full match data was compared using an independent t-test. The level of significance was set at p ≤ 0.05, and all data are reported as mean ± SD. Second, given the practical nature of the study, differences between ball-in-play and full match data were also analyzed using Cohen's effect size statistic (3). Effect sizes of <0.2, 0.2–0.6, 0.61–1.2, 1.21–2.0, and >2.0 were considered trivial, small, moderate, large, and very large, respectively (15). Pearson's correlation coefficient was used to assess the relationship between the total ball-in-play time and relative distance, low-speed activity, high-speed running, and frequency of RHIE. Correlations of 0.10–0.29, 0.30–0.50, 0.51–0.70, and >0.71 were considered small, moderate, large, and very large, respectively (15).
The mean ± SD match time was 84.5 ± 3.0 minutes. The ball was in play for 47.9 ± 4.1 minutes. On average, there were 41 ± 6 stoppages during matches with an average stoppage duration of 49 ± 38 seconds. The average longest ball-in-play period was 223 ± 56 seconds. The longest ball-in-play period from any match was 333 seconds.
Match Activity Profiles
The relative distance covered, low-speed activity, and high-speed running across the entire match irrespective of ball-in-play time was 86.7 ± 9.8 m·min−1, 81.7 ± 9.8 m·min−1, and 5.0 ± 1.8 m·min−1, respectively. When accounting for stoppages in play, the relative distance covered (125.1 ± 16.1 m·min−1), low-speed activity (115.3 ± 15.7 m·min−1), and high-speed running (9.5 ± 2.9 m·min−1) demands were significantly (p < 0.0001) higher (Table 1). The frequency of collisions and RHIE were also higher when accounting for stoppages in play.
Relationship Between Ball-in-Play and Match Activity Profiles
Large positive correlations were found between total ball-in-play time and absolute measures of total distance (r = 0.59, p = 0.001) and low-speed activity (r = 0.60, p = 0.001). Conversely, large negative correlations were found between total ball-in-play time and relative measures of total distance (r = −0.67, p < 0.001) and low-speed activity (r = −0.60, p = 0.001). The correlations between total ball-in-play time and absolute and relative measures of high-speed running, RHIE activity, maximal accelerations, and total collisions were nonsignificant (p > 0.05) and small in magnitude (r = −0.07–0.25) (Table 2).
The purpose of this study was to investigate the activity profiles of semiprofessional rugby league match-play, accounting for time when the ball was “in” and “out-of-play”. The results of this study demonstrate the greater movement, contact, and RHIE demands when rugby league time-motion data are expressed relative to ball-in-play time. Furthermore, a negative relationship was found between total ball-in-play time and relative match intensity; longer total ball-in-play time was associated with lower relative distance and low-speed activity. The reduction in relative intensity with longer total ball-in-play time suggests that during prolonged passages of play, players adopt a pacing strategy to maintain high-intensity performance and manage fatigue.
This study found greater physical demands when time-motion data were corrected for ball-in-play time than if data were expressed relative to the entire game (that also included stoppage time). Indeed, when expressed relative to ball-in-play time, the relative distance covered was 44% greater than if the entire match (including stoppage time) was analyzed. The high-speed running, sprinting, and acceleration demands were 63–90% higher when expressed relative to ball-in-play time. The frequency of total collisions increased by 63%, whereas RHIE activity almost doubled with the frequency of RHIE bouts increasing from 1 bout every 10.7 minutes to 1 bout every 6.1 minutes. Collectively, these findings suggest that time-motion analysis which fails to account for ball-in-play time overestimates the low-speed activity and underestimates the proportion of high-intensity activity performed during match-play.
As expected, greater total ball-in-play time was associated with greater absolute total distances covered. As stoppages in play are generally associated with jogging to take a penalty tap, walking to a scrum, or moving to a field position to either kick off to the opposition (after a conceded try) or receive a kickoff (after scoring a try), the higher total distances were achieved through greater distances at low speeds. Greater ball-in-play time was not associated with absolute high-speed running distances or the absolute number of maximal accelerations, collisions, or RHIE bouts performed. Although the high-intensity activities (i.e., accelerations, high-speed running, collisions, and RHIE bouts) are considered to be the most physically demanding (17) and most likely to contribute to fatigue (17,18,26), sport scientists involved in the recovery of players should be aware of the influence that total ball-in-play time has on the match activity profiles (particularly total and low-speed distance) of rugby league players.
A major new finding of this study was that greater total ball-in-play time was significantly associated with lower relative distance (r = −0.67) and lower relative distance covered at low speeds (r = −0.60). Neither increases nor decreases in total ball-in-play time had an effect on high-speed running, collisions, accelerations, or RHIE activity. As correlational data cannot provide insight into cause and effect, it is difficult to determine whether greater total ball-in-play time reduces relative intensity or a lower relative intensity encourages players to keep the ball-in-play for longer periods. Given that lower-ranked teams have a greater proportion of short duration ball-in-play periods and a smaller proportion of long duration ball-in-play periods than higher-ranked teams (7), these findings suggest that during matches with greater ball-in-play time, players either experience fatigue or adopt a pacing strategy to maintain high-intensity performance.
Although the physical qualities of players were not measured in this study, it is likely that individual fitness levels will affect both the time that the ball is in play and the activity profiles of players. For example, previous rugby league research has shown that players with greater high-intensity intermittent running ability and lower-body strength perform more high-speed running and RHIE during match-play (13,14). In addition, physically dominant teams keep the ball in play longer than weaker teams (7) with the quality of opposition also influencing the activity profiles of match-play (9). It is likely that teams with poorly developed physical qualities experienced greater relative physiological strain during long ball-in-play periods, and consequently, put the ball out-of-play and reduced their low-speed activity (e.g., through kicking the ball over the touch-line and walking to the scrum) either as a tactical strategy or to prevent the onset of fatigue.
In conclusion, this study investigated the activity profiles of semiprofessional rugby league match-play and accounted for the time when the ball was “in” and “out-of-play”. The results of this study demonstrate the greater movement, contact, and RHIE demands of rugby league match-play when time-motion data are expressed relative to ball-in-play time. Furthermore, a negative relationship was found between total ball-in-play time and relative match intensity, with longer total ball-in-play time associated with lower relative distance and low-speed activity. The reduction in relative intensity with longer total ball-in-play time suggests that during prolonged passages of play, players adopt a pacing strategy to maintain high-intensity performance and manage fatigue.
This study described the physical demands of active rugby league match-play by excluding stoppage time from the analysis. A major new finding was the 44% greater relative distance, 63–90% greater amount of high-speed running, sprinting, and accelerations, and 75% greater RHIE activity when data were expressed relative to ball-in-play time. Our findings indicate that the inclusion of stoppage time results in a dramatic underestimation of the physical demands of actual match-play. Given that most sport scientists analyze training activities on a “drill-by-drill” basis and exclude inactive training time (e.g., coach instruction, drinks breaks) (22), any comparison of training and competition demands would result in an artificial increase of training intensity relative to match-play. The present findings are in general agreement with those of White and MacFarlane (30), who demonstrated a 59% greater relative distance covered when hockey matches were analyzed according to time on the pitch, rather than using a full game analysis. Taken with the findings of others (30), the present results suggest that sport scientists involved in the GPS analysis of team sports should consider active playing time when designing training activities to replicate the demands of competition.
The findings of this study provide some obvious practical applications for the strength and conditioning coach. Although previous investigations have reported mean intensities of 90–100 m·min−1 (8,9,11,25,28,29) and ∼85 m·min−1 (10) for elite and subelite rugby league match-play, respectively, the present findings demonstrate 44% greater relative total distance covered when accounting for stoppages in play. In addition, the frequency of collisions and the high-speed running, sprinting, and acceleration demands were 63–90% higher when expressed relative to ball-in-play time. Given the fatiguing nature of collisions (17–19), accelerations (23), and high-speed running (12), prescribing programs based on the “average” demands of match-play (that includes significant stoppage time) is likely to result in players being underprepared for the higher frequency of running, collisions, and RHIE that occur during active match-play. The movement (125.1 m·min−1), high-speed running (9.5 m·min−1), acceleration (1.0 effort per minute), repeated-effort (1 bout every 6.1 minutes), and contact conditioning (0.67 collisions per minute) programs designed by strength and conditioning coaches should reflect the higher physical demands of active rugby league match-play.
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