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Running Demands and Heart Rate Response in Rugby Sevens Referees

Suarez-Arrones, Luis1; Calvo-Lluch, África1; Portillo, Javier2; Sánchez, Francisco2; Mendez-Villanueva, Alberto3

The Journal of Strength & Conditioning Research: June 2013 - Volume 27 - Issue 6 - p 1618–1622
doi: 10.1519/JSC.0b013e3182712755
Original Research

Suarez-Arrones, L, Calvo-Lluch, Á, Portillo, J, Sánchez, F, and Mendez-Villanueva, A. Running demands and heart rate response in rugby sevens referees. J Strength Cond Res 27(6): 1618–1622, 2013—The purpose of this study was to examine for the first time the match running demands and heart rate (HR) responses associated with elite rugby sevens referees. Twelve referees were analyzed over 38 games, using Global Positioning System. Referees covered an average distance of 1665.2 ± 203.5 m per game (15.1 ± 0.5 minutes). Over this distance, 22.3% (371.8 ± 48.9 m) was spent standing and walking, 25.9% (431.2 ± 92.6 m) jogging, 12.4% (206.5 ± 53.2 m) cruising, 23.8% (395.6 ± 94.3 m) striding, 8% (133.3 ± 61.6 m) high-intensity running, and 7.6% (126.7 ± 87.3 m) sprinting. The average maximal distance of sprints, the number of sprints, and the mean sprint distance over the game were 31.3 ± 13.4 m, 5.76 ± 3.6 sprints, and 19.9 ± 7.8 m, respectively. The referee’s work-to-rest ratio was 3.5:1. There were no statistical differences between the first and second half in any of the running variables analyzed. The average HR in the second half (160 ± 9 b·min−1; 86 ± 5% maximal heart rate (HRmax) of the estimated) was higher (p < 0.05) than the HR recorded in the first half (154 ± 11 b·min−1; 83 ± 6% of the estimated HRmax). This study also suggests that the physical demands of referring in rugby sevens are quite different from those encountered in other rugby codes, and the training regimes need to meet the increased overall running demands and high-intensity running activity.

1Faculty of Sport Sciences, Pablo de Olavide University, Seville, Spain

2Faculty of Sport Sciences, University of Castilla La Mancha, Toledo, Spain

3Physiology Unit, ASPIRE, Academy for Sports Excellence, Doha, Qatar

Address correspondence to Dr. Luis Suarez Arrones, ljsuamor@upo.es.

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Introduction

Every rugby sevens match is under the control of match officials who consist of the referee, 2 touch judges and 2 in goal judges or assistant referees. The referee is the sole judge of fact and is required to apply the Laws of the Game in every match (10). As such, decisions taken by the referee during play can determine the final result of the match. The ability of the referee in rugby sevens to keep up with play to be in good position is critical in allowing correct decisions to be made. Thus, the ability of the rugby sevens referee to meet the physical and physiological demands imposed during match play is believed to be a necessary prerequisite for optimal positioning and successful refereeing.

To date, only very limited information exists on the physiological and running demands associated with match play in rugby refereeing. Moreover, previous published data have examined both rugby union and rugby league referees (12,13,15). No data are available yet on rugby sevens refereeing. Recently, the rugby sevens has been voted one of the new Olympic summer sports and will appear in Rio 2016 (8), being this code one of the fastest growing sports.

Despite some similarities with rugby union and league refereeing, the unique features of rugby sevens, including the lower number of players, the same pitch dimensions, and the shorter game duration, likely impose distinct physical and physiological demands. Indeed, recent studies suggest that the physical demands imposed on rugby sevens’ players (9,19,20,21) are quite different from those encountered in other rugby codes (3,5–7,14,16,17). Specifically, rugby sevens is characterized by relatively high running demands intercalated with short periods of recovery which in turn imposes a much faster running tempo than the other rugby codes (9,19,20,21). Understanding refereeing physical and physiological demands during competitive matches will assist in designing specific conditioning programs and physical fitness testing protocols in rugby sevens referees. Accordingly, the aim of this study was to examine for the first time the match running demands and exercise intensity associated with men rugby sevens refereeing.

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Methods

Experimental Approach to the Problem

In this investigation, an observational design was used to examine match running demands and exercise intensity during matches in 2 international rugby sevens tournaments. Twelve referees were monitored during 38 competitive matches. All the referees monitored in this study were refereeing at the top level in Spain or Portugal and some of them also at the top level in Europe. Portable global position system (GPS) technology and heart rate (HR) responses were used to assess match running demands and exercise intensity, respectively. Identification of referee movement patterns and the associated physiological responses during match play is important for optimizing training prescription and managing referee preparation for competition.

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Subjects

Time-motion analysis of running activity was collected from 12 elite male rugby referees (age, 37.1 ± 5.9 years; body mass, 83.7 ± 4.8 kg; height, 175.5 ± 6.2 cm). All referees had a minimum of 4 years of rugby sevens refereeing experience. Written informed consent was obtained before their participation. The experimental protocol was approved by the Institutional Ethics Committee (Pablo de Olavide University).

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Experimental Procedures

Match analyses were performed 2–4 times on each referee during a total of 38 matches played during 2 international rugby sevens tournaments. All matches were played on the same standard outdoor natural grass fields with 7 players per side. Playing time was 2 halves of 7 minutes each.

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Activity Pattern Measurements

The referees were asked to carry a GPS unit (SPI Pro X; GPSports Systems, Canberra, Australia) during the game, which fitted to the upper back (i.e., between the shoulder blades) of each referee using an adjustable neoprene harness The devices were switched on minutes before the game and immediately switched off at the end. The data stored include HR, time, speed, and distance. Global position system data were recorded at 15 Hz frequency and accelerometer data to 100 Hz. The validity and reliability of the GPS system (1 Hz) have been previously reported with a coefficient of variation of 1.7% (4). Additionally, a recent study (1) has shown the appropriateness of GPS technology for the evaluation of referees’ activities. Despite the absence of a gold standard method (2) to confirm GPS validity, the use of GPS in this study was deemed appropriate considering its good reliability (4) and use in prior studies of players and referees (19,20).

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Match Running Demands Analysis

Time-motion data from all referees who completed the entire first and second halves were retained (n = 38 files from 12 different referees). After collection, all match data were analyzed with the software designed to provide objective measures of physical match performance. The referees’ activities were coded into the following categories and speed thresholds: standing and walking (0.1–6.0 km·h−1), jogging (6.1–12.0 km·h−1), cruising (12.1–14.0 km·h−1), striding (14.1–18.0 km·h−1), high-intensity running (18.1–20.0 km·h−1), and sprinting (>20.1 km·h−1). The speed thresholds for each category were the same as those reported previously in rugby sevens (19,20,21) and union (6) players using the GPS technology. The above categories were divided into 2 further locomotor categories to provide an estimation of referee work-to-rest ratios: (a) low-intensity activity (0.1–6.0 km·h−1) and (b) moderate- and high-intensity activity (>6.1 km·h−1) (19,20,21). The frequency of high-speed zone entries (sprints > 20 km·h−1) and the highest speed recorded during the game were also collected. Average speed (km·h−1) was also calculated from the total distance covered in each half, divided by the time spent on the pitch for each individual referee. Match running performance was analyzed by comparing the first and second half.

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Exercise Intensity

Match exercise intensity was quantified by monitoring HR during each match. Heart rate was continuously measured with short-range telemetry (SPI Pro X; GPSports, Canberra, Australia) and was expressed in relation to the individual maximal heart rate (HRmax) estimated through the formula of Tanaka et al. (22). In those referees whose HRs were higher in the course of the match than estimated HRmax, the HRmax values obtained during the game were retained and used in the analysis. As previously employed in rugby sevens players (19,20,21), HR data were classified based on the percentage of total playing time spent in each of the following 6 HR zones: zone 1 (<60% HRmax), zone 2 (61–70% HRmax), zone 3 (71–80% HRmax), zone 4 (81–90% HRmax), zone 5 (91–95% HRmax), and zone 6 (>96% HRmax).

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Statistical Analyses

Data are presented as mean ± SD. Differences between the first and second halves were determined using Student’s dependent t-test. Differences between distance covered at different running intensities and time spent at different HR intensities were analyzed using a 1-way analysis of variance with repeated measures. When a significant interaction was found, Bonferroni’s adjusted post hoc tests were applied. All analyses were carried out with SPSS 18.0 (SPSS, Inc., Chicago, IL, USA) software with the level of significance set at p ≤0.05.

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Results

Movement Analysis

The average total distance (± SD) covered by the referees throughout the game (15.12 ± 0.51 min) was 1665.2 ± 203.5 m with a range of 1332–2002 m. As a percentage of total distance, 22.3% (371.8 ± 48.9 m) was covered standing or walking, 25.9% (431.2 ± 92.6 m) jogging, 12.4% (206.5 ± 53.2 m) cruising, 23.8% (395.6 ± 94.3 m) striding, 8% (133.3 ± 61.6 m) at high intensity, and 7.6% (126.7 ± 87.3 m.) sprinting. There were no significant differences (p < 0.05) between the first and the second half in different zones (Figure 1).

Figure 1

Figure 1

The average speed obtained during the game was 6.6 ± 0.8 km·h−1, and there were no significant differences (p > 0.05) between the first and the second halves: 6.7 ± 0.8 km·h−1 vs. 6.5 ± 0.8 km·h−1. Referee’s work-to-rest ratio was 3.5:1 (i.e., for every 3.5 m covered at moderate- and high-intensity speed [>6.1 km·h−1], 1 m was covered at low intensity [0.1–6.0 km·h−1]). Table 1 displays sprinting performance results obtained during matches. There were no significant differences (p > 0.05) between the first and the second halves in any parameter analyzed.

Table 1

Table 1

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Exercise Intensity

The average HR in the first half (154 ± 11 b·min−1; 83 ± 6% of the estimated HRmax) was lower (p < 0.05) than in the second half (160 ± 9 b·min−1; 86 ± 5% HRmax of the estimated). The referees attained average values of HRmax of 174 ± 11 b·min−1 (94 ± 5.9% of the estimated HRmax) with higher HRmax recorded in the first half than in the second half (176.6 ± 10.2 vs. 170.8 ± 12.2 b·min−1, p < 0.05). Figure 2 shows the percentage of playing time spent in each exercise intensity zone expressed as percentage of the estimated HRmax during each half. Referees spent most of their playing time in zone 4 (i.e., between 81 and 90% HRmax) with significant differences observed between halves in several HR zones (Figure 2).

Figure 2

Figure 2

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Discussion

This is the first study to characterize the match running demands and associated physiological strain (i.e., estimated via HR recordings) of referees during rugby sevens competition. As previously reported in rugby sevens players (19,20,21), the referees evaluated in this article were exposed to higher running demands than their counterparts refereeing other rugby codes (12,15). Compared with video data collected in rugby league (12) and union (15) referees, the current group of rugby sevens referees covered substantial greater total distance per minute (110 m·min−1) in comparison with approximately 79 m·min−1 in rugby league and 101 m·min−1 in rugby union. Moreover, with the same technology used in this study (i.e., GPS), it was found that male rugby sevens players covered a total match distance per minute (113 m·min−1) (19). Although the comparison between different studies should be made with caution, because of the different time-motion analysis methods employed, the higher and similar overall running demands observed in rugby sevens compared with other rugby codes referees and rugby sevens players, respectively, have implications for the physical preparation of referees wishing to transfer between the different rugby codes.

The lower number or frequency of game-related non-locomotive activities such as rucks or scrums are believed to be partially responsible for the augmented running demands in rugby sevens in comparison with the other rugby codes (11). The work-to-rest ratio, which reflects total high running speed exercise vs. total low running speed exercise time, reported in this study (i.e., 3.5:1) is substantially higher than what could be estimated from the data reported in rugby league (1.6:1) (12) and rugby union referees (0.6:1) (15), suggesting that the relative moderate to high-speed demands in rugby sevens are higher than in rugby league and rugby union refereeing. Also the higher work-to-rest ratio reported in rugby sevens referees, the moderate to high-speed demands, is still higher in rugby sevens refereeing (86 m·min−1) compared with the rugby union referees (72 m·min−1) (12). This provides further support to the notion that rugby sevens referees have to be prepared to cope with a much higher running demands than the other rugby codes.

Players’ sprint and high-intensity activity are considered to be important during match play (18), and the same may also be true for the referees in determining the outcome of a game. While experience in tactical positioning to follow the game may affect a referee’s movement patterns, there will be periods in a match when the referee will be required to cover ground very quickly to be close to the action and make accurate decisions. The referees in this study spent 15.6% of their movement time in activities of high intensity (>18 km·h−1) or sprint (>20 km·h−1) during a rugby match which is higher than approximately 7% of the total movement time (i.e., excluding the time referees were standing still; approximately 37%) spent "running" and "sprinting" by rugby union referees (15). Furthermore, these figures presented here are slightly higher than the 13.7% reported in men rugby sevens players (19) using the same technology. The average number of sprints (>20.1 km·h−1) reported in this study was approximately 6 per match (Table 1), which is similar to approximately 7 sprints performed by male rugby sevens players (19). Similar to rugby sevens players, referees are also required to sprint over average distances of approximately 20 m and occasionally over distances longer than 40 m. This implies that specific sprint training should reflect these demands and both short (≤20 m) and long sprints (40–50 m) to mimic the demands of the game.

The average HR of the referees in this study was approximately 84% of the estimated HRmax, which is slightly lower than approximately 86–89% of the estimated HRmax reported in the rugby league referees (13) and approximately 88% HRmax obtained in male rugby sevens players (19). Moreover, and despite the similar running demands that rugby sevens players (19) and referees (this study) have, the latest spent substantially less playing time at intensities above 90% of the estimated HRmax (38 vs. 22%, respectively). Although speculative, it is possible that the non-locomotor high-intensity activities, such as tackles, pushing/pulling in rucks, and scrums that players have to carry out but not the referees, can be responsible for the reduced HR responses observed in rugby sevens referees compared with the players.

In summary, this study described for the first time the running demands and associated physiological responses to rugby sevens refereeing. This study shows that rugby sevens refereeing is characterized by relative high running demands. This study also suggests that the running demands of rugby sevens are typically higher than those encountered in other rugby codes referees and comparable to rugby sevens players. These findings provide important information for prescription of training aimed at developing physiological qualities specific to the demands of competitive men rugby sevens referees.

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Practical Applications

The assessment of the external load (i.e., running demands) and internal load (i.e., HR responses) imposed during the actual competition is the first step preceding the design of specific conditioning programs in rugby sevens referees. The training regimes of contemporary rugby sevens referees need to meet the augmented overall running demands and high-intensity running actions observed in rugby sevens referees in comparison with rugby league and union. As such, the development of appropriate levels of intermittent aerobic fitness is recommended.

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Keywords:

GPS technology; match-play demands; high-intensity running; sprint

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