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Repeated High-Intensity Exercise in a Professional Rugby League

Austin, Damien J; Gabbett, Tim J; Jenkins, David J

Journal of Strength and Conditioning Research: July 2011 - Volume 25 - Issue 7 - p 1898-1904
doi: 10.1519/JSC.0b013e3181e83a5b
Original Research
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Austin, DJ, Gabbett, TJ, and Jenkins, DJ. Repeated high-intensity exercise in a professional rugby league. J Strength Cond Res 25(7): 1898-1904, 2011—The primary aim of this study was to identify and describe the frequency and duration of repeated high-intensity exercise (RHIE) bouts in Australian professional rugby league (National Rugby League) and whether these occurred at critical times during a game. Time motion analysis was used during 5 competition matches; 1 player from 3 positional groups (hit-up forward, adjustable, and outside back) was analyzed in each match. The ranges of RHIE bouts for the 3 positional groups were hit-up forwards 9-17, adjustables 2-8, and outside backs 3-7. Hit-up forwards were involved in a significantly greater number of RHIE bouts (p < 0.05) and had the shortest average recovery (376 ± 205 seconds) between RHIE bouts. The single overall maximum durations of RHIE bouts for the hit-up forwards, the adjustables, and the outside backs were 64, 64, and 49 seconds. For all groups, 70% of the total RHIE bouts occurred within 5 minutes prior of a try being scored. The present data show that the nature of RHIE bouts was specific to playing position and occurred frequently at critical times during the game. These results can be used to develop training programs that mimic the ‘worst case scenarios’ that elite rugby league players are likely to encounter.

1School of Human Movement Studies, The University of Queensland, St. Lucia, Australia; 2Sydney Roosters Rugby League Club, New South Wales, Australia; and 3School of Exercise Science, Australian Catholic University, Brisbane, Australia

Address correspondence to: Damien Austin, damiena@sydneyroosters.com.au.

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Introduction

Recent studies that have used time motion analysis (TMA) in professional Rugby League have confirmed that the accumulated distances sprinted by players during most games is relatively small compared to the total distances they cover in a match through forward or backward walking, jogging, and striding (5-7). Although it is recognized that sprinting and repeated sprinting are central to the game and some research groups have suggested that repeated sprint ability (RSA) is a critical determinant to the outcome of a match (5,9,10), the occurrence of repeated high-intensity exercise (RHIE) relative to points scored is yet to be specifically addressed in Rugby League.

Research into high-intensity exercise, particularly in Rugby League, has been confined to the assessment of high-intensity running; tackling, for example, has not been included in evaluating the role and importance of high-intensity exercise. Given the exacting and demanding nature of tackling (coupled with the high frequency of tackles during a match), it is suggested that tackling be included in any further assessment of high-intensity exercise demands. Moreover, many previous studies that have provided information on sprint and multiple sprint activities in field sports have reported average values rather than the most intense scenarios (2,4,5,9,10). However, it is maximal values that need to be built in to any training program developed as a result of TMA; using average data to develop training programs is not likely to best prepare players for the most intense periods of play they are likely to experience in competition. The purpose of this study was therefore to examine the nature (durations and frequencies) of RHIE in professional Rugby League and consider whether these occurred at critical times relative to points scored during a match. Tackling and sprinting were assessed with the view that the findings could inform the development of training practices that could prepare players for the most demanding passages of play likely to be experienced in a game.

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Methods

Experimental Approach to the Problem

Time motion analysis was used to evaluate the nature and frequency of RHIE undertaken by professional Rugby League players over several games. An RHIE bout was defined as 3 or more sprints, tackles or combination of both with <21 seconds recovery between high-intensity efforts (modified from Spencer et al. [10] to include tackling).

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Subjects

The movement patterns of 15 players from a professional rugby league club were recorded during 5 National Rugby League (NRL) games played in Australia during the 2008 season. This number of participants was greater than those used by King et al. (5) and similarly used by Sirotic et al. (10) with 17 players. Games were chosen 5 weeks apart (±1 week) from January to September, and all were played at Suncorp Stadium, Brisbane. After consultation with the coaches, players were clustered into 3 positional groups. Five players in each of the 3 positional groups were assessed. The associated players in these positions were hit-up forwards (prop and second row), adjustables (halfback, hooker, five-eighth, and lock), and outside backs (fullback, wing, and center). All subjects provided written informed consent before data collection. Ethics approval for all experimental procedures was granted by the Ethics Committee of The University of Queensland.

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Procedures

Video recordings were made using 3 cameras (Hitachi DZ-GX5060SW, Hitachi Ltd., Tokyo, Japan) positioned on stationary tripods. Cameras were positioned on the half-way line approximately 30 m above the playing field. This allowed a full view of the entire playing field. Each camera operator followed 1 designated player for the entire duration of each match investigated.

The zoom function of each video camera allowed each player to be filmed with a minimal radius of 10 m so as to allow a view of his surroundings and field position. Each player was filmed for the entirety of the match, including breaks in play and time on the bench. The filming of 5 matches allowed for the averaging of data for each grouped playing position, differences in environment, oppositional standard and variations in refereeing.

The video footage was analyzed using a simple hand-notation game analysis system; for each movement activity, frequency, distance covered, and duration were recorded. Movement was coded as 1 of 8 speeds of locomotion (standing, forward walking, backward walking, forward jogging, backward jogging, forward striding, forward sprinting, and lateral movement), one state of nonrunning intense exertion (e.g., tackling) or 1 discrete activity (e.g., kicking). These codes have been further defined previously (King et al. [5]). The uses of field markings (10-m lines and sidelines) were used to reproduce as closely as possible the player's location, speeds, and distances in activities.

High-intensity work was considered to include forward striding, forward sprinting, and tackling. Low-intensity work included standing, forward and backward walking, and forward and backward jogging and lateral movement. Low-intensity activities were considered rest periods as opposed to high-intensity activities that were classified as exercise. The duration of each interval of high-intensity work was divided by the duration of the following rest interval. This gave an exercise-to-rest ratio for that passage of play or game. An RHIE bout was defined as 3 or more sprints, tackles or combination of both with <21-second recovery between high-intensity efforts (modified from Spencer et al. [10] to include tackling).

Reliability of the TMA method was assessed by having another operator perform repeat analyses on one-half (ca. 40 minutes) of footage from 1 player. Intertester reliability was assessed by comparing analysis files from the 2 coders for the first analysis, while comparing the repeated analyses for coders assessed intratester reliability. Each experimenter was denied knowledge of results by the other experimenters, and approximately 4 weeks separated the first and second analyses for intratester reliability. The imprecision of the coding technique was assessed using the typical error of measurement (TE) (8). Previous studies have applied this method of reliability to TMA in rugby (3) and hockey (11).

Typical error of measurement calculations were based on 4 measurements (frequency, total time, relative time [%], and relative distance [%]) of the 10 key movement modes (standing, forward walking, backward walking, forward jogging, backward jogging, striding, sprinting, lateral, tackling, and kicking). The TE (%) values for intracoder reliability for frequency, total time, relative time (%), and relative distance (%) were 2.6, 0.4, 9.3, and 5.2, respectively. The TE (%) values for intercoder reliability for frequency, total time, relative time (%), and relative distance (%) were 1.4, 0.2, 7.8, and 6.7, respectively.

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Statistical Analyses

Data for duration, percentage time, total time, number of activities, and mean duration and frequencies for activities and high-intensity exercise, are presented as means and SDs. The RHIE data were assessed through raw data calculations to format frequency, duration, activity profiles, and also duration from a try being scored. Analysis of variance was used to establish differences in the variables among playing positions and residuals were checked for normality. If a difference between playing positions was found, a post hoc test (Tukey) was then used to locate the difference. All statistics were run on SPSS v17.0 for Windows with an alpha of 0.05 set a priori. Based on an alpha level of 0.05 and a sample size of 5 (number of players per position), the beta level (power) was >0.80 for detecting effect sizes of 0.5 or greater among individual playing positions for relative sprint distance (%), relative sprint duration (%), and relative time in high-intensity efforts (%).

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Results

Number of Repeated High-Intensity Exercise Bouts per Game

Hit-up forwards were involved in a significantly greater (p < 0.05) number of RHIEs (12 ± 3) when compared to the adjustables and outside backs (6 ± 3 and 5 ± 1, respectively) (Table 1). There was no difference between the adjustables and the outside backs in total number of RHIE bouts in the first and second halves of the games (3 ± 3 and 3 ± 2, and 2 ± 0 and 3 ± 1, respectively; p > 0.05). However, there was a difference for the hit-up forwards in the total number of RHIE bouts between the first and second halves of the games (7 ± 2 and 5 ± 4, respectively) (p < 0.05), which is likely because of the less time spent by this group on the field during the second half of the games.

Table 1

Table 1

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Total Duration of Repeated High-Intensity Exercise per Game

The mean total times spent in RHIE per game for the hit-up forwards, adjustables, and outside backs were 374 ± 96, 145 ± 94, and 120 ± 39 seconds, respectively (Table 1). The hit-up forwards and adjustables tended to have greater total mean durations of RHIE in the first half (220 ± 88 and 81 ± 79 seconds) when compared to the second half of the games (154 ± 129 and 64 ± 55 seconds) (p > 0.05). For the outside backs, the mean total durations of RHIE bouts for first and second halves were 43 ± 9 and 77 ± 36 seconds, respectively (p > 0.05).

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Average Maximum and Overall Maximum Durations of Repeated High-Intensity Exercise

The mean maximum duration of RHIE bouts was higher for the hit-up forwards (53 ± 8 seconds) than for both the adjustables (39 ± 16) and the outside backs (34 ± 11 seconds) (p < 0.05) (Table 1). The single overall maximum durations of RHIE bouts for the hit-up forwards, the adjustables, and the outside backs were 64, 64, and 49 seconds, respectively.

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Number and Type of Activities in Overall Maximum Repeated High-Intensity Exercise Bouts

The hit-up forwards and adjustables had a significantly greater number of activities (20 and 17 efforts, respectively) in a single RHIE bout than the outside backs (9 efforts) (p < 0.05) (Figure 1). However, the hit-up forwards tended to spend the least amount of time in high-intensity efforts, such as sprinting and tackling (30%) within their maximal RHIE, compared to the adjustables and outside backs (41.2 and 55.5%, respectively), although this was not statistically significant (p > 0.05). The outside backs tended to have the least percentage of efforts spent tackling (45.5%) when compared to the adjustables and hit-up forwards (58.8 and 60%), although this also was not statistically significant (p > 0.05).

Figure 1

Figure 1

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Percentage of Sprinting and Tackling Efforts in Repeated High-Intensity Exercise

The hit-up forwards tended to have a higher percentage of their RHIE spent tackling (57%) than sprinting (43%), although this was not statistically significant (p > 0.05). The percentage of tackling for the hit-up forwards was significantly greater (p < 0.05) than for the adjustables (49.4%) and outside backs (40.5%). The adjustables spent almost the same amount of time sprinting and tackling (50.6 and 49.4%) in RHIE bouts. Based on the summation of RHIE activities, sprinting for the hit-up forwards (43%) was significantly less than for both the adjustables (50.6%) (p < 0.05) and outside backs (59.5%) (p < 0.05) (Figure 2).

Figure 2

Figure 2

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Distances Sprinted

The majority of sprints for all positional groups were over a distance of 6-10 m (46.1, 39.4, and 32.4% for the hit-up forwards, adjustables, and outside back groups, respectively). For the hit-up forwards, the percentage of sprints over 6-10 m was significantly greater than for the adjustables (p < 0.05), and outside backs (p < 0.05). Hit-up forwards also sprinted more 11- to 20-m distances than the outside backs (p < 0.05). Of the sprints, 81.3% completed by the hit-up forwards were over 20 m or less, whereas the adjustables completed 82.7% of their sprints over 20 m or less (compared to 65.4% for the outside backs) (Figure 3). There was no significant difference in sprinting distance >21 m between the 3 positional groups.

Figure 3

Figure 3

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Recovery between Repeated High-Intensity Exercise

The hit-up forwards tended to have the shortest recovery (376 ± 205 seconds) between RHIE bouts compared to the adjustables (442 ± 304 seconds) and outside backs (820 ± 567 seconds), although, probably because of the high SDs, these values were not significantly different between groups (p > 0.05) (Table 1). The adjustables and outside backs had the same minimum RHIE recovery durations (55 seconds, respectively), with the hit-up forwards minimum RHIE recovery time tending to be less (42 seconds) (p > 0.05).

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Repeated High-Intensity Exercise Relative to Tries Scored

The team studied won 3 of the 5 games played; the team scored 25 tries and 24 goals (conversions), whereas the opposition teams scored 18 tries and 17 goals. During the 5 games, the studied team attempted no field goals.

All 3 playing positions had relatively similar percentages of their total RHIE bouts occur within 60 seconds of tries being scored; outside backs had the highest percentage of total RHIE at 12%, compared to hit-up forwards (11.3%) and adjustables (10.7%) (p > 0.05). The percentage of total RHIE bouts immediately preceding (0 seconds) a try was highest for the hit-up forwards (6.5%), followed by the adjustables (3.6%); there was no RHIE bout that immediately preceded a try for the outside backs. Therefore, of the 3 positional groups, hit-up forwards engaged in 80% of the total number of RHIE immediately before a try (0 seconds). When RHIE bouts occurred within 30 seconds of a try being scored, the only percentage change was found for the hit-up forwards; 9.7% of the total RHIE bouts completed by the hit-up forwards occurred within 30 seconds.

Within 60 seconds of a try being scored, the hit-up forwards carried out 53.8% of the total RHIE bouts completed by the 3 positional groups. Both the adjustables and outside backs completed 23.1% of total RHIE bouts within 60 seconds of a try. The outside backs had the greatest percentage (44%) of total RHIE bouts that occurred within 5 minutes (<300 seconds) of a try being scored. This compares to 37.5% for the adjustables and 32.3% for the hit-up forwards (Figure 4). For all groups, 70% of the total RHIE bouts occurred within 5 minutes prior of a try being scored.

Figure 4

Figure 4

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Discussion

The aims of this study were to identify and describe the frequency and duration of RHIE bouts in professional rugby league and consider whether these activities occurred at critical times during a game (i.e., immediately before points being scored). The present data show that the nature of RHIE bouts was specific to playing position and occurred frequently at critical times during the game.

The ability of players to repeat high-intensity exercise (similar to ‘RSA,’ proposed by Spencer et al. [10]) is recognized as being central to elite performance in field sports that are characterized by intermittent sprints. Indeed, some researchers have suggested that RHIE bouts occur at critical phases of a match (1,9).

The range of RHIE bouts over the 5 games for the 3 positional groups in this study were hit-up forwards 9-17, adjustables 2-8, and outside backs 3-7. The hit-up forwards spent an average of 26.6% less time on the field than the adjustables and outside backs, yet they completed a significantly greater number of RHIE bouts per game. The shorter game time for the hit-up forwards almost certainly reflects the very high-intensity nature of the work demanded of them when they were on the field. These positional ranges are significantly greater than the 0-3 range of repeated sprints (RSA) reported in rugby league by Sirotic et al. (9). The inclusion of tackling with sprinting in the present study significantly increases the estimation of high-intensity exercise that players engage in. Given the known high physical demands of tackling, coupled with the importance of this particular skill on the outcome of a game, one can reasonably argue that any assessment of high-intensity exercise in rugby league must include tackling and sprint exercise.

King et al. (5) reported that the average high-intensity exercise time performed by their players without rest was 4 seconds, with the longest exercise period being 35 seconds. The data reported by King et al. (5) are single efforts of high-intensity exercise, and not a collection of 3 or more high-intensity efforts, such as RHIE used in this study. This study showed the average duration of RHIE bouts over the 5 games was the same for the adjustables and outside backs and averaged 24 seconds; RHIE bouts for the hit-up forwards averaged 30 seconds. When the average maximum duration of RHIE bouts over the 5 games are considered, the hit-up forwards were engaged for a maximum of 53 seconds. In contrast, the maximum durations of RHIE bouts for the adjustables and outside backs were 39 and 34 seconds, respectively. The present maximal RHIE data show that average data do not accurately reflect the most intense passages that a player is likely to experience in a game. For players to be adequately prepared for the most intense passages of play, they are likely to experience in competition, conditioning coaches need to use maximal values rather than average values to design their training programs.

The most intense single RHIE bout based on total duration was achieved by an adjustable, at 64 seconds. This involved 6 high-intensity activities (4 sprints and 2 tackles), and the player covered a total distance of 104 m. There were 17 changes in activity and sprint distances ranged from 8 to 12 m. The most intense single RHIE bout achieved by a hit-up forward lasted 64 seconds but involved 20 activities. Ninety meters were covered during this bout (including 1 sprint of 7 m), and the player completed 5 tackles. For the outside backs, the most intense RHIE bout lasted 49 seconds, covered a total distance of 66 m, and included 9 activities; 5 of these were high-intensity in nature, and there were 3 sprints ranging from 10 to 18 m in addition to 2 tackles.

Although previous research (5,9,10) has reported the frequency of RHIE involving sprints, the duration between a player required to perform another RHIE bout has not been studied. Of the 3 positional groups, the hit-up forwards had the shortest average recovery (376 seconds) between RHIE bouts; recovery for the adjustables and outside backs averaged 442 and 820 seconds, respectively. The minimum RHIE recovery durations for the adjustables and outside backs were the same (55 seconds, respectively), whereas the minimum RHIE recovery time for the hit-up forwards was 41.7 seconds.

For all 3 positional groups, the majority of their RHIE bouts involved 3 high-intensity activities, such as sprinting and tackling. The hit-up forwards and adjustables were involved in a majority of RHIE bouts that included 1 sprint and 2 tackles (29.5 and 37% of RHIE in total). The configuration of 2 sprints and 1 tackle was the second highest combination of efforts in an RHIE bout for hit-up forwards and adjustables (16.4 and 22.2%, respectively); however 2 sprints and 1 tackle comprised 58.3% of total RHIE for outside backs. This demonstrates the need to include tackling, as a high-intensity effort, as opposed to just sprinting referred to by Sirotic et al. (9) as tackling plays an important facet for the varying playing positions.

This study found for the 3 positional groups, most sprints (39.3%) were over distances of between 6 and 10 m, followed by distances of between 11 and 20 m (28%). These distances are shorter than those reported by Meir et al. (6); those authors found that most sprints were between 10 and 20 m. Meir et al. (7) do not comment on changes in average sprint distances after the 10-m rule was introduced. The present findings are similar to those of King et al. (5) who found that hit-up forwards generally sprinted 5-6 m, whereas the adjustables generally sprinted 8-12 m. The outside backs generally sprinted greater distances, but ranges were not reported by the authors (5). In this study, both the hit-up forwards and adjustables completed over half of their sprints (55.4 and 51.7%, respectively) over distances <10 m; 38.2% of the sprints completed by the outside backs were over a distance <10 m. Eighty percent of all sprints completed by the hit-up forwards and adjustables were <20 m in distance, whereas the outside backs completed 80% of their sprints over distances <30 m. Outside backs were found to have the highest percentage of sprinting distance over 40 m (at 9.8% of their total sprints), compared to 4.7 and 4.5% for the same distance covered by hit-up forwards and the adjustables. These findings impress the need for training programs to take into account that most sprints in a game occur over distances <20 m for hit-up forwards and adjustables, and over slightly longer distances (30 m) for outside backs.

Both Spencer et al. (10) and King et al. (5) suggest that bouts of particularly high-intensity exercise (e.g., RHIE) are often critical to the outcome of many games, influence points being scored and also occur close to either the opposition goal line (in attack) or the defending goal line. Hit-up forwards were found to performed 86% of all RHIE bouts within 30 seconds of a try being scored. By comparison, 23% of RHIE bouts for the adjustables and outside backs occurred within 30 seconds of a try being scored. When the 3 positional groups were considered together, 70% of RHIE bouts occurred with 5 minutes of tries being scored. The proximity of RHIE bouts to tries scored not only varied relative to positional group but there were also differences relative to whether their own team scored or whether the opposition scored. For the hit-up forwards, 55 and 45% of RHIERIHE bouts occurred within 5 minutes of tries being scored by their own team and the opposition team, respectively. For the adjustables 67 and 33% of the RIHE bouts occurred within 5 minutes of their own team scoring a try and the opposition scoring a try (respectively). The outside backs were found to have the greatest percentage of RHIE bouts preceding their own tries; 83% of RHIE bouts occurred within 5 minutes of a try for this group. Outside backs therefore had a greater percentage of RHIE bouts immediately before their own team scoring, as opposed to hit-up forwards for whom there were roughly equal percentages of RHIE bouts that occurred in attack and defense.

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Practical Applications

This study has shown the importance of RHIE bouts in relation to points being scored and that the duration and activities of RHIE bouts differ relative to playing position. The present data can be used to develop training programs that mimic the ‘worst case scenarios’ (in the context of RHIE demands) that elite rugby league players are likely to encounter in competition. Training programs should replicate the different RHIE activities the various positions use most frequently. Training programs that develop each player's capacity to frequently undertake RHIE with minimal periods of recovery may be expected to influence the outcome of a game.

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Keywords:

time motion analysis; training; intermittent exercise

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