INTRODUCTION
Decisions made by team sport officials can have a direct impact on the match outcome (60,62). Since rugby union (rugby) achieved professional status in August 1995 (55), there have been numerous rule changes, considerable developments in match analysis, and improvements in physical and technical training (69). The recent, rapid evolution of the sport has resulted in many match changes, for example, a reduction in the amount of participation time per player (69). Investigators studying rugby players are currently using more complex methodologies and larger match samples (70). Such trends reflect increasing competitiveness as teams strive for performance advantages over their opponents. Unsurprisingly, these changes have also resulted in increased physical demands on, and therefore requirements of, rugby referees (47,61). Interestingly, similar changes in requirements for other team sport officials have been reported, including Association Football (soccer in some countries) (85), Australian Football (AF) (21), and National Rugby League (NRL; rugby league) (39,66).
Much of the requirements of these sports are best described as high-intensity intermittent exercise (HIIE) (5), which involves bursts of high-intensity exercise interspersed with extended periods of low-intensity recovery. The general description of the physical requirements placed on athletes during HIIE typically includes physiological responses (such as heart rate [HR]) and work rate demands (such as locomotion speed [Sp]). These requirements make a significant contribution to the development of strength and conditioning programs and the types of physical assessments used. Appreciating how energy systems are engaged in various athletic activities should result in physical programs being designed to meet the actual demands of each specific sport (13,26,60). Although the relationship between the physical demands of officiating, resultant fatigue, and decision making (DM) is complex (35), professional rugby referees are engaging in decision-training activities to improve accuracy and consistency. Understanding how the physical behaviors of these individuals relate to DM is critical and will help to inform such training activities (31,35,56).
This article reviews the available research based on rugby referees involved with the 15-a-side game, and more specifically, the physiological response and work rate demand profiles during games in the context of other major team sport match officials. It also highlights the limited pool of information that currently exists concerning this unique subgroup of athletes. This information is then used to discuss current research reports on DM, physical monitoring assessments, and strength and conditioning programs used with rugby referees, and subsequently, identifies areas that warrant further research with this cohort of athletes.
METHODS
LITERATURE SEARCH
Articles relating to refereeing 15-a-side rugby union were the focus of the search criteria. The search engines used through the months of January–December 2016 for this review article included: PubMed; Te Puna—Index NZ; SPORTDiscus; Google Advanced Scholar; Scopus; and Summon (multiple database search—Physical Education). All searches were restricted to peer-reviewed journal articles and conference proceedings. Terms used for the sporting codes presented included: Rugby Football and/or rugby union and/or Rugby; AF League and/or Australian Rules Football and/or AF and/or AF and/or VFL; Rugby League and/or NRL; Soccer and/or Football and/or Association Football. A variety of Boolean phrases were then used with the various sport codes to search under these key areas:
- Refereeing: Officiating and/or officials; umpiring and/or umpires and/or field umpires; touch judges and/or assistant referees.
- Response: Reaction and/or demand and/or physical demand and/or performance.
- Work rate: Speed and/or distance and/or time-motion analysis and/or kinematic demands and/or activity profile.
- Physiological: HR and/or cardiovascular and/or physiological strain.
- DM: cognition, perception, match analysis, motor skills, perceptual cognitive
- Assessment: Monitoring and/or testing
- Training: Conditioning and/or physical work
Additional articles were also found by reviewing the reference lists from retrieved studies.
INCLUSION AND EXCLUSION CRITERIA
No restrictions were imposed on publication date or publication status. Studies were limited to the English language. Searches for AF and rugby league officiating investigations revealed a paucity of articles, similar to 15-a-side rugby union. By comparison, there were a larger number of soccer investigations. Soccer articles chosen were those that represented the physical requirements of refereeing at an elite level.
PHYSIOLOGICAL RESPONSE
HR monitoring is convenient and noninvasive (14) and has been recorded and analyzed in officials from a number of HIIE team sports. Five published investigations have described the HR response of rugby referees (19,24,47,48,61) and 2 conference proceedings (10,45). The researchers reported, among other variables: (a) mean HR (HRmean); (b) HR response as a percentage of maximum HR (%HRmax); and (c) HR response as a relative time percentage (relative time %) working in various HR zones as a %HRmax. Similarly, another 5 research groups have documented the HR response of refereeing rugby league (11,35,39,44,66), and for AF, 1 editorial (65) and 1 publication (34). Comparatively, there has been considerably more research studies undertaken that have examined the HR response of those involved in officiating soccer; 13 published articles in total (8,17,23,37,40,49,50,52,57,78–80,86).
HR data from team sports officials reveal that most match time HR response is categorized in the “work” zone, typically >80% HRmax, as reported with rugby referees (Table 1). Despite the range of extraneous factors influencing HR, for example, anxiety (44) and match experience (59), HR measurement has been shown to be fairly reliable, practical, and cost-effective as a method to assesses physiological stress (49,79). Rating of perceived exertion (RPE) does present practical difficulties, for example, coach buy-in (1). Despite this, a significant relationship between mean match HR and match RPE scores has been reported when subjects used RPE regularly (79). Validity of RPE has also been confirmed recently as an indicator of global internal training load (physical and psychological stress) (73). Accordingly, resultant adjustments in match official movement pattern behavior to conserve energy (8) can explain some of the discrepancies with reported physiological data. Level of competition and/or match official age can also contribute to these on-field physical adjustments. Older officials have been shown to keep up with play, despite a reduced overall physical match performance compared with those younger officials (59). This suggests an improved game sense, which aligns with findings from an investigation where contender rugby referees spent more time in the low-intensity HR zones and completed increased time jogging and sprint activity compared with provincial referees (47). Similarly, Weston et al. (2006) reported intensities with the higher level competitive soccer leagues. It would seem that these articles suggest that there are 2 key factors to consider: first, the level of competition; and, second, the game sense developed by a referee over time. It is obvious then that higher levels of competition require more physical work, likely due to pace of play, which—when combined with game sense—contributes to the work engaged in by the referee.
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Table 1: Rugby union referee physiological response
Table 1-A: Rugby union referee physiological response
HRmean values for rugby referees are, overall, quite consistent in the literature, with an average of approximately 153–154 beats per minute (bpm) (39,61), although an investigation with club level matches in South Africa by Kraak et al. (2011b) revealed surprisingly low HRmean responses (122–141 bpm) for 2 different levels of officials (Table 1). Explanations for this might include the structure and level of play (week-long tournament/club) and resulting match-play demands on players, together with the experience and conditioning level of the referees. However, overall, rugby referee values are similar to those reported for soccer (53) and rugby league (39). Although mean HR data are useful, a better scope of understanding about physiological response is gained when this value is converted to a percentage of maximum HR (%HRmax).
From the %HRmax data, it can be observed that rugby referees usually work within a range of 80–90% HRmax (Table 1), which represents hard work (87). Although reduced levels at 68–76% HRmax (Table 1) were reported from club level matches in Stellenbosch (48), in general, these values suggest that referees require high levels of aerobic fitness. Subelite rugby referees recorded a mean value of 85 ± 3.5% HRmax (Table 1) (24). To date, this is the highest % HRmax recorded for rugby officials; this was likely due to subelite level and inferior physical condition. Hoare reported a mean value of 81% HRmax for professional rugby league referees (39). By contrast, this reduced value could be a reflection of their professional status and superior physical condition. Interestingly, values from highly ranked match officials in football have ranged from 85% (51) to 96% HRmax (17). This range demonstrates the impact of competitive level on HR response as matches ranged from top league to junior (under 21) competitions. Overall, the reduced values could be attributed to enhanced physical condition or reduced level of competitive play, whereas those elevated indicate the more continuous style of play in soccer compared with other HIIE team sports. Importantly, the method by which HRmax has been calculated (direct measure versus indirect estimation) needs to be acknowledged because this may contribute to the variation in the reported data.
When times spent above and below specified zones at percentages of maximum HR are examined, the understanding of HR response is extended further. Time spent at varied HR zones (Table 1) provides an indication of the anaerobic nature of officiating rugby revealing that for most of the game, HR is spent in the work zone (>80% HRmax). Martin et al. (2005) reported 53% of game time in the “work zone” for English Premiership rugby referees compared with 64% from a more recent investigation into Super 12 Rugby referees (10). This suggests that the Super 12 Rugby competition placed a higher level of stress on the oxygen transport system and/or their level of hard aerobic conditioning is inferior. Other contributing factors might include style of play and increased professionalism from 2005 to 2011. Interestingly, an investigation into English FA Premier League referees revealed that 53% of time was spent in the 80–90% HRmax zone alone (80). By comparison, those referees in the Super 12 Rugby study spent a smaller fraction of their time (42%) in this zone. Again, such a difference may provide further evidence of the contrasting physiological requirements when officiating different codes and even different competitions in different parts of the world at the highest level and/or the nature of the game itself.
WORK RATE: SPEED AND DISTANCE DEMANDS
Time and motion analysis (variations which are known as notational or match analysis) typically includes modern, portable microsensor equipment such as global positioning system (GPS) units and digital video, which allow for tracking of athlete movement in naturalistic environments (47,62). This technology has revealed that experienced officials (those officiating at an international level) seem to conserve energy and possess a heightened ability to anticipate play (47).
Test level rugby referees have been shown to cover less distance running backward when compared with those officiating at a provincial level (46). Other factors that influence the work-rest activity pattern include: the level of physical conditioning (15); game intensity dictated by player activity, and therefore, match requirements (9,17,29); and the resultant level of physical fatigue (12,60). When these factors are combined with the varied methodologies used by investigators, the speed-distance discrepancies that have been reported are better understood. Despite such limitations with what has been reported, motion analysis can still benefit the design of strength and conditioning programs and assessment criteria that help to optimize game performance (13,26,44,60). Furthermore, benefits from these programs are then obtained when the conditioning stimulus represents or overloads the actual response and demand that is required by the game (24,86).
There are 4 published investigations in which the work rate demands of rugby referees have been studied (19,47,48,60), and 2 conference proceedings (10,46). More specifically, these researchers have reported distance traveled and speed obtained within various locomotor categories. By comparison, there are 5 known publications in which the work rate demands of rugby league referees have been reported (11,35,39,43,66) and 3 recent AF publications (21,33,34). Similar to HR response, there have been more research studies on the work rate demands of those involved in officiating soccer and, more recently, investigators have started to examine positioning and DM performance (56).
From the time and motion analysis techniques used in these investigations, it would seem that the majority of both distance traveled and time spent completing various movement activities is within the low-intensity “rest” zone, as observed with rugby referees (Table 2). Typically, this is set at <3.6 m·s−1 and has involved standing still, walking, jogging, and utility patterns (sideways and backward). Kelly et al. (46) reported that a sample of elite-level international and provincial rugby referees spent up to 93% of total playing time in the “rest” zone (Table 2). This value is similar to an investigation with provincial referees in New Zealand (19) (Table 2). These are greater than those of 77–80% observed in English Premiership (61), Super Rugby (10) (Table 2), and AF (21), respectively. Although the soccer researchers most often report speed over a percentage of playing distance, the majority of the total distance traveled is in the rest zones (standing, walking, and jogging), for example, 60% (59). Furthermore, these “rest” zones are characterized by frequent bouts of high-intensity activity. Inconsistencies in the reported measures can, in part, be explained by the lack of standardized speed zones or definitions within or between sports (22). Varied game styles and rules of play would also help explain the variations in data within and between sports.
Table 2: Rugby union referee work rate demand
The distances traveled by rugby referees during match play have been shown to reach 8,518 ± 668 m (60) (Table 2). Not surprisingly, this value is greater than the range of distances (5,139–6,389 m) that have been reported for Super 14 rugby players (3), as rugby referees, such as soccer officials, need to keep up with play at all times (75). Super Rugby referees traveled an average distance of 8,000 m (Table 2), more than the 6,200 m covered by international rugby referees (46) (Table 2). This may have been due to the more experienced referees being extra economical with their running patterns and/or the nature and pace of international versus provincial games. Rugby league referees have been shown to travel distances of 6,700 m (43), similar to international rugby referees. Although these 2 codes involve different game styles, the lengths of each game are the same (80 minutes). By comparison, officials in soccer and AF consistently travel distances exceeding 11,000 m (21,33,85), which is primarily due to the continuous nature of play. Other factors—such as length of play, rule changes and style of play, and pitch size—have been offered as further explanations for the difference in distance covered by match officials across various sports.
DECISION MAKING AND HIGH-INTENSITY INTERMITTENT EXERCISE
Researchers have reported that matches impose high levels of physical demand on team sport officials, including soccer (14,82), AF (21,34), rugby league (39,66), and rugby union (48). DM is considered the most important role of officials during competitive matches because it ensures that games are played in a fair and safe manner, although also upholding the integrity of the game (38). Understanding how DM relates to physical performance is critical; however, this relationship is complex and multivariate and needs to involve a number of key considerations, for example, player fatigue (35).
There is a paucity of research that has quantified this relationship, both within games, for instance, AF (32,33), soccer (56,62), and rugby league (31,35) and using simulations (e.g., in AF and rugby league (31)). Although this DM relationship has not been investigated with rugby referees, global accuracy success rates have (63,64). These authors report measures of accuracy of 54% with top-20 group referees in a naturalistic setting using video. This is similar to the success rates, again using video, reported for subelite AF umpires, but is below the elite umpires (54), which at 61% is similar to that reported for soccer referees. These officials reported on incidents at a national level (62), which increased to 86% when judging foul play at international levels (56). Although these investigations encourage the need for meaningful training, they lack detailed information regarding the actual match performance of officials. There has been no research conducted within rugby union games or using match simulations; however, findings from other team sport officials can provide some further insight and understanding.
An investigation with AF and rugby league match officials used a simulation to investigate psychomotor performance (31). Traditionally, an inverted U curve has been used to describe the relationship between steady-state and incremental exercise, but the investigators challenged whether this was suitable for HIIE. Psychomotor performance improved during the simulated bouts of high-speed running (HSR), where cerebral hemodynamics (30) is likely to play a role through increased cerebral blood flow and nervous system arousal. With this increase in psychomotor performance, however, the physical performance measures reduced. During a real match, the official may not have the option of reducing these measures because it has been suggested that this could compromise positioning (32). Although we are aware that player physical activity does vary within matches (20,27,34), there are no known investigations that have linked this to match official physical performance and DM. This advanced level of inquiry would help reveal whether or not reported declines in physical activity toward the end of a match, for example, as reported with soccer referees (59,83) and AF umpires (34), are in response to the reduced demands of play and/or physical fatigue. Consideration is needed around how these reductions in running to accommodate fatigue might influence optimal positioning to view play and make decisions.
Fatigue is believed to accumulate during real soccer matches (6) and errors have been shown to occur twice as often in the second half (56). Furthermore, DM has been shown to have a moderate drop in accuracy during the final 10-minute period while officiating soccer compared with the opening period (62). Contradicting this, poorer DM has also been reported in the first 15 minutes of soccer matches (62), which suggest that fatigue is not the only contributing factor. Other variables to consider include the relative predictability of the game, the official's movement speed (68), and changes in psychological arousal (18). By comparison, findings from a rugby league investigation (35) suggest that physiological and movement demands of refereeing in real matches have no significant effect on adjudication of penalties. This was similar to a finding from a study with AF umpires (33) where DM accuracy with free kicks was consistent across the 4 quarters. Only 1 type of decision, however, was assessed in these investigations; therefore, it cannot be representative of total DM.
Limitations also occur with the research that has used simulations, which lack the real context that match officials are challenged with; for example, varied distances from play and obstructed views that might impact DM (56). Simulations provide no opportunity for a change in some movement activities that might be typical of real matches. This might provide some explanation around improved psychomotor performance with the simulation used for both rugby league and AF where utility movements were not included. Utility movements have a greater physiological cost compared with forward movements at the same speed (77); therefore, it makes sense that in real match play, reductions in utility movements have been reported to conserve HSR (23). Consequently, it has been suggested that more experienced match officials have a superior ability to read play and predict positions for themselves (13). Also, the relationship in real matches is examined in a global manner and it is problematic to assume that no relationship exists. Rather, more sensitive time periods (5-second and 10-second analysis) need to be explored and the influence of external crowd noise and player fatigue on performance needs consideration. In such instances, transient fatigue over short periods may have some influence over DM. A key question that could be asked is: “What interference on psychomotor performance happens in the short period before and after an HSR event?” The response to this would be especially interesting in relation to rugby referees because this would include player interference, which is likely to be more than most other team sports because of the rules and nature of play. Recently, researchers studying AF umpires have suggested that HSR events may have a negative effect on psychomotor performance (31), with practical implications (31) including:
- Portion of training time pressurized and physical activity incorporated,
- Stimulate stress response, and
- Manage emotional and physical states.
PHYSICAL MONITORING
GENERAL MEASURES
Criterion measures for elite-level male and female rugby referees have been developed (hereafter referred to as standards) for each assessment presented (Table 3). These standards are categorized as Optimal (Green “flag”), Acceptable (Orange “flag”), or Unacceptable/Undesirable (“Red” flag).
Table 3: General measures: rugby union referee criterion measures
The creation of standards, and then monitoring individuals against these standards, is widely recognized as a method to assess training progress over time (88). Although the “flags” provide an indication of a referee's current status for each measure, the real value comes as a result of monitoring the collective general measures over a period and in relation to specific physical individual goals. Accepting that there is a range of influencing factors to consider in the development of such standards, the following will discuss how these standards were identified and discussed in comparison with other related data.
Aerobic power
Yo-Yo intermittent recovery test level 1 (Yo-Yo IRL1) is frequently used to assess aerobic power (84). Yo-Yo IRL1 provides an indirect indication of the physical capacity of intermittent team sport athletes (51). When the standards for the Yo—Yo IRL1 were established, they were used globally to assess the ability of team sport athletes to repeatedly perform and recover from intense activity. It is within this context that this test is used for referees, that is, a measure of the referees' capacity to repeatedly perform and recover from intense activity.
As can be observed from Table 3, acceptable Yo-Yo levels for male and female rugby referees are around levels 18 and 15, respectively. Regarding the male data, a review of the Yo-Yo IR Test (7) reported mean values for top- and moderate-elite male soccer referees of >2,000 m (>L18.07) and 1,700 m (>L17.08), respectively, which was similar with 1,800 m (L18.02) from an earlier investigation with top-level soccer referees (16). It would seem that the aerobic standards deemed acceptable in rugby are similar to those of elite male soccer referees, although soccer running distances can exceed 11,000 m (86), which is much greater than that reported for rugby. By comparison, Yo-Yo distances of 1,000 m (L15.06) were reported for moderate-elite female soccer referees (7), which is more similar to the standards deemed acceptable for female rugby referees.
Speed
Sprinting involves a fast release of muscular energy to move an athlete forward at maximum speed (74). Rugby referees need the ability to move at speed, given fast passages of play, and position themselves appropriately to make decisions (60). Importantly, it has been reported that fast 40-m sprint times have construct validity for the physical assessment of soccer referees (81). Subsequently, this assessment has been used for rugby referees, that is, measure of the referees' ability to move quickly to ensure optimal positioning to make decisions.
As can be observed from Table 3, acceptable standing 40-m times for male and female rugby referees are less than 5.30 and 5.80 seconds, respectively. Standing 40-m sprint has been adopted widely to assess speed with team sport athletes (players and officials), with a range of 5–6 seconds for elite intermittent high-intensity sport participants (28).
Repeated speed
Repeated-sprint ability (RSA) is recognized as an important physical ability in team sport performance (25,36). The RSA protocol was developed with guidelines used to monitor soccer referees and represents the ability to repeat high-intensity efforts during a match (81). Given the rationale and the nature of rugby union, this test was also used with referees, that is, measure of the referees' capability to repeat short high-intensity bouts of work.
As can be observed from Table 3, acceptable mean modified phosphate decrement test (Mod PDT) times for male and female rugby referees are less than 5.20 and 5.70 seconds, respectively. Similar to speed, GPS data collected with rugby referees have clearly showed the repeated-sprint activity engaged in matches (10). In comparison with the other general measures, the standards were more challenging to set because of a lack of teams sport data, especially regarding match officiating. The standards were set with these limitations in mind.
Anthropometry
Anthropometric measures are recognized as being critical parts of the holistic monitoring for athletic performance (72). These measures were, therefore, also used for referees, that is, it measures the referees' physical shape and indirectly affects quality and ease of movement during a game.
As can be observed from Table 3, acceptable body mass index (kg/m2) measures are ≥24 to <30 for male and female rugby referees with waist circumference (cm) ≥92.0 to <102.0 and ≥72.0 to <88.0 and sum 7 skinfolds (mm) ≥70.0 to <100.0 and ≥80.0 to <110.0 for male and female referees, respectively. These measures are based on guidelines from the American College of Sports Medicine (42), combined with the techniques described by the Guidelines for Athlete Assessment in New Zealand Sport (41).
SPECIFIC MEASURES
Global positioning system data
GPS is now used widely among a variety of team-based sports and provides sport scientists, players, and coaches with valuable information about both the training and competition environment (22). A growing amount of literature has investigated the validity and reliability of the units. These investigations have shown that as the technology has evolved, the accuracy of measuring a variety of work rate demands, such as acceleration and deceleration, has improved. Importantly, the precision of GPS units has had to evolve because there is an ever increasing need from practitioners to measure and assess a wide variety of movement activity; for example, the use of metabolic power has been reported to represent the energetics associated with high-speed acceleration and deceleration (67). Used correctly, this type of detail can further enhance strength and conditioning programs for a wide range of athletes, including referees.
Since 2009, GPS has been used to track the locomotion of elite male rugby referees in matches and create movement profiles of the physical demands of the sport. Conditioning coaches have been able to use individual-appropriate profiles to increase the specificity of prescribed physical activities (2). These specific measures align with the outcomes from the paucity of rugby referee investigations presented in this brief review. Importantly, they demonstrate the HIIE nature of this activity. Maximum estimated speed and HR are calculated from the standing 40-m sprint and Yo-Yo IRL1, respectively. Although it is accepted that there are difficulties in the classification of speed as a % of maximum because of the widely reported and varied locomotor zones (22,82), these were created using available literature (50,58). This approach is preferred because the use of uniform-speed thresholds fails to individualize match activities and therefore does not provide accurate detail around movement activity (82). The creation of HR zones as a % of maximum HR was deemed to be less problematic, as this process is more commonly completed in applied settings and aligns better with accepted practice (49,75).
TRAINING RECOMMENDATIONS
Although this article focuses on elite-level rugby referees, it also enables aspiring referees to better understand the physiological response and work rate demands at the highest level. Findings from this brief review, combined with current physical monitoring measures, provide opportunity for the development of individualized strength and conditioning programs for rugby referees. Information and measures presented here clearly demonstrate that rugby refereeing is an HIIE; therefore, the development and use of highly intermittent training activities is critical.
Intermittent running activities should focus on 3 key abilities: aerobic power; anaerobic capacity; and anaerobic power. Current-reported elite-level GPS match measures indicate that there is a range of demand and response patterns. This illustrates both the variation between referees and the type of match being officiated. Strength and conditioning coaches should consider designing programs using the below variables as guidelines for the desired intensity:
- High-intensity speed (>51% Spmax);
- High-speed acceleration and deceleration (2.5–6 ms2);
- Sprint (surge) (>80% Spmax);
- Metabolic power (W/kg); and
- High-intensity HR (>80% HRmax).
Individual referee maximums can be established from general measures. Maximal speed and high-speed acceleration and deceleration can be calculated from the standing 40-m (88) and maximal HR from the Yo-Yo IRL1 (84). All 4 measures require a maximal effort and can be recorded accurately with 10-Hz GPS units (71). Although there are no available rugby referee training studies, HIIE has been shown to improve levels of soccer referee physical capacity, and therefore, match performance (88). Maximum aerobic speed sessions are time efficient and can be used to develop aerobic power (4), whereas repeated sprint (76) and sprint activity (81) can develop anaerobic capacity and anaerobic power, respectively.
A typical training week (Table 4) should aim to include 2–3 HIIE sessions, which engage multidirectional movement to mimic match patterns (37). Importantly, a portion of the training efforts during the week should overload the referee and include some decision-making activity (31). Although detail on training load and periodization is beyond the scope of this review, travel is a major challenge that this subpopulation of athletes deals with regularly and makes load planning programming problematic.
Table 4: Example target preseason training week schedule for a professional male 15-a-side rugby union referee
Combining this research with a better understanding of the relationship between physical activity and DM, as well as the use of intermittent running activity will hopefully enable the rugby referees to keep up with play while accumulating less fatigue, allowing for optimal positioning from which to make accurate decisions.
SUMMARY
Officiating team sports is an HIIE activity. Essentially, this involves high-intensity activity interspersed with low-intensity efforts. Elite-level rugby referees are monitored using a remote program that assesses both general and specific measures. Although the protocols and use of these measures is informed by the literature and the normative data collected, practical considerations also have a contribution to make. General measures provide opportunities to assess the conditioning programs being used by rugby referees with indication on physical ability during a match. By comparison, the specific measures from GPS inform specific in-match physical achievements that also contribute to program design. Although the relationship between DM and physical activity needs more investigation, the importance of individualized and specific strength and conditioning programs is widely accepted.
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