Rugby League is a collision sport involving frequent bouts of high-intensity exercise (sprinting, tackling, and running) separated by bouts of low-intensity exercise (walking and standing) (12). There is a lack of information regarding the physiological demands and movement patterns of elite Rugby League players during match play. One way to determine the physiological demands of Rugby League and quantify player movement patterns during match play is via time-motion analysis incorporating the use of match video recordings performed retrospectively (15,19,20,24).
Meir et al. (19,20) performed a retrospective analysis of professional Rugby League match video recordings under the preexisting 5-m (19) and current 10-m (20) defensive rules. Although Meir et al. (19,20) reported that the majority (84-95%) of match play consists of low-intensity activities such as standing, walking, and jogging, the nature of elite Rugby League match play requires players to perform high-intensity activities such as accelerating, directional changes, sprinting and withstanding physical collisions during offensive and defensive phases of play. Early studies (19,20) of Rugby League match play were limited by small sample size, the number of positions examined, and changes to defensive and interchange rules.
Recent studies (15,24) have added to our understanding of the physiological demands of professional Rugby League; however, no studies have examined player movement patterns under current player interchange rules or the 2-referee system introduced to the National Rugby League (NRL) in 2009. A greater understanding of the specific demands imposed upon players during match play is needed to develop Rugby League-specific training and recovery programs, to facilitate optimal on-field performance and reduce the risk of injury.
The limitations of time-motion analysis using match video recordings in Rugby League and other football codes have been reported (7,9). Although traditional video tracking methods quantify player movement during competition, the use of varied and inconsistent categories to describe player movement patterns could have compromised our information on the physiological demands and movement characteristics of match play in Rugby League. The labor-intensive nature of retrospective video recording analysis and the failure to operate in real time, may make such video analysis prone to measurement error and prolong assessment of player performance indicators (8,10). As more advanced technologies for performance analysis emerge, there is a need for a concomitant increase in the evaluation and analysis of that information to improve training practices and reach desired performance outcomes.
Recently, the development of portable global positioning system (GPS) units designed for athlete tracking have provided an alternate data acquisition method to determine the demands of training and competition in real time (6,14,17,18,21,28) with the potential to overcome some of the limitations associated with traditional methods. The GPS is a satellite-based navigation system that permits quantitative measurement of player position, velocity, heart rate (HR), and movement patterns through traditional GPS triangulation methods, accelerometer, and HR monitoring software (10). Investigation of Rugby League match play incorporating portable GPS units provides scope for a better understanding of the positional specific physiological demands of competition to optimize training rationales and facilitate on-field performance.
To our knowledge, no study has reported Rugby League match-play movement characteristics using GPS technology. The absence of GPS acquired match-play data in Rugby League may be because of concerns about the accuracy and reliability of portable GPS for high-intensity field sports, the size and positioning of the GPS receiver on the player, and the perceived risk of injury associated with the GPS unit during match play (8). Recent advances in GPS technology (23) have increased the accuracy and reliability of the GPS during team sports (10,17,18,21). Furthermore a reduction in the size of the GPS unit has made it less intrusive, so it can be worn safely during Rugby League match play.
Uncertainty exists regarding the movement patterns and physiological demands of elite Rugby League match play under current rule structures, player interchange limits and the introduction of 2 referees in the NRL. The aim of this study was to (a) examine the physiological demands elite Rugby League match play using portable GPS technology to monitor a player's movement patterns and HR; (b) examine positional comparisons to determine if a player's physiological requirements are influenced by their playing position during Rugby League match play. We hypothesize that there will substantial positional differences in movement patterns and exercise-to-rest ratio activities during elite Rugby League match play. Further, the use of portable GPS will provide a more detailed and specific analysis of player movement patterns, high-intensity and low-intensity match-play activities, and HR response to the demands of Rugby League match play than achieved previously.
Experimental Approach to the Problem
Global Positioning System technology was used to examine the independent variable of player movement characteristics to determine position-specific running profiles during elite Rugby League match play. To examine the physiological response of the dependent variable during match play, HR was measured using a portable chest strap HR monitor. The GPS and HR data were collected from players during 5 regular season NRL matches of 80-minute duration. All participants played a minimum of 30 minutes of match play in each of the 2 40-minute halves of each match. Players were separated into forwards and backs for positional comparison. An understanding of player movement patterns and HR during match play is important for monitoring performance and effectively planning and managing player preparation for the rigors of competitive match play.
Twenty-two elite male Rugby League players, age 24.2 ± 7.3 years, height 188 ± 20.1 cm, and mass 94.6 ± 26.8 kg (mean ± SD), representing an NRL team volunteered to participate in this study. Because of the minimum on-field match participation requirements, data were analyzed from 15 players (Forwards n = 8; Backs n = 7) during each match (Total 5 match subjects: Forwards n = 40; Backs n = 35). Before the commencement of the study, participants attended a presentation outlining the purpose, benefits, and procedures associated with the study. Written informed consent was obtained from all participants. The study was approved by the Bond University Human Research Ethics Committee.
Global Positioning System Units
This study used commercially available GPS receivers (SPI-Pro, GPSports, Canberra, Australia), which operated in a nondifferential mode and provided data in real time. The SPI-Pro GPS units measure at 5 Hz and contain a triaxis integrated accelerometer, which measures accelerations in gravitational force (G force) on 3 planes, namely, forwards and backwards, up and down, and tilt left and right. The GPS model used in this study (76 g; 48 mm × 20 mm × 87 mm) was worn in a purpose designed vest (GPSports) to ensure that range of movement of the upper limbs and torso was not restricted. Manufacturer guidelines (GPSports) report the effective distance of the GPS units used in this study for data collection as 200 m from the field of play. The GPS unit was worn in a padded mini backpack contained in the vest and positioned in the center area of the upper back slightly superior to the shoulder blades at approximately the level of thoracic vertebrae 1 (T1).
Participants had previously worn GPS units in outdoor training sessions that included Rugby League specific running, skill-related and match-simulated contact activities during a 16 week preseason training period. Participants had also worn the units in 2 preseason practice games before the commencement of the NRL regular season of competition. No participants complained of any discomfort or impediment to their normal range of movement or performance from wearing the equipment during training or competitive match play. Data provided from the GPS unit included total distance, speed, and HR characteristics. Positional data of players wearing GPS units are recorded via comparison of travel time of radiofrequency signals emitted from at least 4 earth orbiting satellites (16). Player speed profile data are determined via measurement of the rate of change in the satellite's signal frequency because of GPS unit movement characteristics (Doppler Shift) (23). Raw accelerometer data were available in real time via Wireless Fidelity communication and were displayed using commercially available software (Team AMS, GPSports).
The validity and reliability of GPS and integrated accelerometry to measure distance and speed during high-intensity exercise that characterizes contact and noncontact sports have been reported (2,4,10,17,21,29). The reliability of the SPI-Pro has previously been tested at our laboratory over distances from 5 to 8,000 m on a synthetic 400-m athletics track with variations of <3% and the reliability of speed assessed with electronic light gates (Smart-Speed, Fusion Sport, Australia) from walking speed (6 km·h−1) to a maximum sprint speed (>20.1 km·h−1) with variations of <5.5%. Our results are similar to those of others who have reported the reliability of the SPI-Pro GPS (21).
Movement Classification System
A zone classification system forms the basis of the analysis by the Team AMS software, allowing 6 ranges of speed (m·sec−1 or km·hr−1) and HR (b·min−1) to be set and used for analysis. Zone 1 indicates the lowest effort or lowest velocity of movement with each zone progressively categorizing effort and movement intensity to zone 6, which represents the highest effort and intensity of movement. The movement classification system used in this study was based on methods used in Rugby Union (7) and modified to consider forward, backward, and lateral ambulatory movement only. No attempt was made to quantify movement characteristics associated with contact sport-specific movements such as tackling, wrestling, jumping, and scrimmaging in this study. The frequency and duration of entries into each movement zone have been reported to provide a more precise profile of activity patterns among playing position (forwards and backs) in intermittent sports (14).
Each movement zone was coded as 1 of 6 speeds of locomotion (Table 1). The aforementioned categories were subdivided into 2 further locomotor categories to provide a crude estimate of player exercise-to-rest ratios. Standing, walking, and jogging were considered to be low-intensity activities (<12/km·h−1/rest), while cruising, striding, high-intensity running, and sprinting were regarded as high-intensity activities (>12/km·h−1/exercise). The duration of each interval of high-intensity exercise was divided by the duration of the following rest interval to determine exercise-to-rest ratio for that passage of play.
Match HRs were recorded from each player by a commercially available HR monitor using chest straps for electrode placement (Polar Electro, Kemple, Finland). The HR signals were transmitted to the GPS unit positioned between the players' shoulder blades. All participants were accustomed to wearing HR chest straps before data collection. Participants had worn HR chest straps in outdoor training sessions that included rugby league specific running and game simulated contact activities, during a 12-week preseason training period. The data were categorized into HR zones using Team AMS software (GPSports) (Table 2). No participants complained of any discomfort or impediment to their normal range of movement or performance from wearing the HR monitor. Individual maximum HR was recorded as the highest HR achieved during match play.
The statistical software package SPSS version 14.0 was used for the data analysis. Differences in HR, running speed, and distance traveled between backs and forwards during match play were determined using Student's unpaired t-test. A Student's paired t-test was used to determine the differences in HR, running speed, and distance traveled within the backs and forwards during the first half and second half of match play. To determine differences in the distance traveled in the different speed zones and the percent time in each HR zone, a repeated-measures analysis of variance was used to compare between backs and forwards for the first and second halves and the whole game. Significant differences were located by a Bonferroni post hoc test. Significance was accepted when p ≤ 0.05. All data are expressed as mean ± SD.
There was no significant difference in the total distance covered during competitive match play between backs (5,573 ± 1,128 m) and forwards (4,982 ± 1,185 m) (Table 3). The backs covered more distance at high-intensity running (147 ± 46 m; p = 0.03) and sprinting speeds (293 ± 55 m; p = 0.03) during the whole match compared to the forwards (80 ± 32 and 152 ± 28 m, respectively) (Table 4). First half analysis revealed no significant difference in the total distance covered between the backs and forwards (Table 3); however, backs covered more distance at sprinting speeds (121 ± 28 m; p = 0.04) compared to the forwards (73 ± 18 m) (Table 4). Second half analysis found no significant difference in the total distance covered between the backs and forwards. The backs covered more distance at medium-intensity running or striding (278 ± 58 m; p = 0.03), high-intensity running (91 ± 21 m; p = 0.005) and sprinting speeds (185 ± 45 m; p = 0.03) compared to the forwards (174 ± 61, 41 ± 19, and 86 ± 23 m, respectively) (Table 4).
Backs achieved greater maximum running speed during the first half (p = 0.001), second half (p = 0.0002) and over the course of the whole match (p = 0.0002) compared to the forwards (Table 3). During the first half of each match, backs had a greater total duration of sprinting (p = 0.03), had less time between sprints (p = 0.04), and covered greater total distance sprinting (p = 0.03) than did forwards. Similarly in the second half of each match, backs had a greater number of sprints (p = 0.01), had less time between sprints (p = 0.03), a greater total duration of sprinting (p = 0.03), and covered a greater total distance sprinting (p = 0.01) than forwards did. The whole match speed profile for players from all matches found that backs completed a greater number of sprints (p = 0.02) had less time between sprints (p = 0.02), covered a greater total duration of sprinting (p = 0.04), and achieved a greater total distance sprinting (p = 0.02) than did forwards (Table 5) during match play. There was no significant difference in exercise-to-rest ratios of 1:6 and 1:7 for the backs and forwards, respectively, determined from distance covered in each speed zone during the whole match.
There was no significant difference in the maximum and average HRs achieved during either half of match play or during the whole match analysis for backs in comparison to forwards (Table 3). Forwards spent a significantly greater percent of time with HR > 170 b·min−1compared to backs during the whole game (p = 0.02) and during the first (p = 0.02) and second halves (p = 0.04) of match play. Backs spent a significantly greater percent of time with HR <90 b·min-1 compared to forwards during the whole game (p = 0.04) and during the first (p = 0.03) and second halves (p = 0.04) (Table 6) of match play.
This study found no significant difference in the total distances covered between backs and forwards in either half of match play. The total mean distances covered by players in this study are less than in some other studies (19,20) but similar to recent work that has used match-play video recordings to assess movement patterns in elite Rugby League players (15,25). The discrepancy with early studies (19,20) could partly be because of advancements in match-play analysis technology, defensive rule changes, and recent changes to player replacement and interchange rules. Comparison of first and second half running distances indicates that the intensity of match play was maintained throughout each match with no deterioration of running ability or physiological fatigue evident among all playing positions during match play.
Although there was no significant difference in the total distance covered between backs and forwards during match play, there were significant differences in the running speeds used to cover the distances recorded from players of those positions. Backs covered greater distances with high-intensity running and sprinting compared to forwards in each half and during full match analysis. Similar results have been reported elsewhere with backs spending more time in high-intensity activities than forwards (15). The significant difference in high-intensity running and maximal sprinting during match play is most likely because of the requirements of positional play between forwards and backs in Rugby League. Forwards are positioned in close proximity to the center of play, whereas the backs are located in the outer edges and sidelines on either side of the field. The closer proximity of forwards to the center of play tends to avail players in those positions to run shorter distances (ca. 5-12 m ) at high speed to perform match-specific tasks such as a tackling and ball carrying. Alternatively, backs are often positioned with greater space between themselves and the opposition and therefore cover greater distances to come into contact with an opponent and have the added task of sprinting to perform kick return and kick chase activities (15).
Our finding that backs traveled further at higher speeds in comparison to forwards throughout each whole match is consistent with the findings of others (15) and is influenced by greater opportunity to achieve high-intensity and sprinting speeds by backs. The majority of match play for both positional groups was spent performing low-intensity activities. Our findings are consistent with those of others who have reported a predominance of low-intensity activity during Rugby League match play (15,19,20) and support the implementation of Rugby League-specific training programs that involve repeated high-intensity exercise interspersed with periods of low-intensity activity to prepare players for the demands of match play.
In support of studies that have reported backs to be consistently faster than forwards over 40 m (3) and the maximum running speed of Rugby League players (12), backs achieved faster running speeds during competitive match play in comparison to forwards in this study. Backs completed a greater number of sprints (running speed > 5.6 m·s−1) during the match (19 ± 6 vs. 11 ± 5, respectively), backs also sprinted for a greater total duration (44.7 ± 9.1 vs. 25.8 ± 9.2 seconds), and they covered greater distances at maximum speed (321 ± 74 vs. 153 ± 38 m) compared to forwards. Overall, the data indicate that backs participate in a greater amount of higher intensity activity when compared with forwards and are consistent with the results of others (6,24).
There was no significant difference in the average sprint duration during each match between backs and forwards in this study (3.05 ± 0.87 and 2.88 ± 0.91 seconds, respectively). These values are similar to the average sprint duration reported from rugby union forwards and backs and equates to sprinting distances of approximately 20-30 m (7) and imply that the ability to accelerate rapidly is highly important in elite Rugby League match play. Although these data represent average sprint durations, players are regularly required to sprint distances <30 m (24). Time between sprints was higher than expected with forwards displaying significantly longer periods between sprint efforts in both halves and during the whole match compared to backs. The prolonged periods separating sprint efforts seen in forwards may be because of players in these positions regularly running distances that are insufficient to achieve maximal sprinting velocity (<15-20 m) in comparison to backs. The varied sprint profiles identified in this study for forwards and backs supports the need for positional specificity in speed training for elite rugby league match play.
The exercise-to-rest ratios determined from distance covered in each speed zone during match play was 1:6 and 1:7 for the backs and forwards, respectively. These values are lower than those in earlier reports (20) but are similar to those of recent studies (15). The discrepancy between our results and those of others may partly be because of the classification of positional groups, player ability, and fitness levels and differences in the methods used to assess movement during match play. Although exercise-to-rest ratios provide important information on match play demands, exercise-to-rest ratio data calculated from player activity may underestimate actual exercise time and as such data obtained from contact based team sports must be viewed with some caution. Ratios of 1:6 and 1:7 indicate that players are not required to perform repeated high-intensity efforts (<1:2 exercise-to-work ratios) and receive substantial opportunity for rest during low-intensity activity in between high-intensity exercise efforts. The results of this study however are representative of the total distance covered during the game and do not reflect periods of play that may involve repeated or continuous periods of high-intensity exercise (26). Our results are based on the speed associated with match-play activity and do not consider substantial time spent participating in Rugby League-specific pushing, pulling, wrestling, and scrums that register as low-intensity activity using GPS technology despite intense exercise being performed in a stationary position. Exercise-to-rest ratio provides information on the intermittent nature of Rugby League running activity, it may not be a true reflection of actual exercise rates during match play. Nevertheless, the exercise-to-rest ratios in this study and in other studies (15,24) indicate that most of the energy required to perform the periods of high-intensity activity is derived from the adenosine tri-phosphate - creatine phosphate (ATP-CP) system and anaerobic glycolysis (13).
There was no significant difference in the maximum and average HR achieved during competition between the backs and forwards. The average HR of the players in this study is approximately equal to those of players averaging over 70% of their maximum oxygen consumption (O2max) for the duration of match play. The present results indicate that the metabolic demands of elite Rugby League are high. Esposito et al. (11) and others (1) have suggested that HR values can be converted to O2 using the relationship between HR and O2 obtained during treadmill running. Although elevations in HR may overpredict aerobic demand during high-intensity exercise (22), the measurement of HR has been shown to be a valid and reliable method of determining the intensity and physiological demands during team sports (11) and an appropriate index of overall physiological strain during Rugby League match play (5).
Although there was no significant difference in the average HR between backs and forwards in either half of match play or during each whole match, analysis of the time spent in each HR zone reveals that forwards spend a larger percent of time in both halves and during the whole match with HR > 170 b·min−1. This equates to over 85% of maximum HR and is consistent with values of previous research (5). The average HR for players in this study are also similar to values reported for subelite Rugby League players (5) and support the traditionally held view that there is a large aerobic component required for the performance of competitive Rugby League (19,20).
Our finding that there was no significant difference in the distance covered by backs and forwards during match play yet there was a greater amount of time spent in the higher HR zone suggests that the forwards were engaged in more high-intensity activity other than running during match play, a view supported by King et al. (15). Upper body exercise such as tackling, wrestling, and scrimmaging involve the upper body musculature and have been shown to produce higher HR and physiological strain compared to lower body activities performed at similar intensities (27). Backs spent significantly more time with HR < 90 b·min−1 during each first half period and during each whole match compared to forwards. The greater amount of time with an HR < 90 b·min−1 is most likely because of the nature of the positional play of backs whereby more time is spent standing/walking in the defensive and offensive line compared with forwards that are predominantly involved with moving the ball in the middle of the playing field (15). Our results indicate that forwards might need a higher O2max than backs to meet the competitive demands of elite Rugby League.
A better understanding of the demands of elite Rugby League match play is required to improve the analysis of individual performance characteristics and implement a systematic approach to the development of position-specific training programs. Our results indicate that elite Rugby League players are required to complete frequent bouts of high-intensity activity separated by short bouts of low-intensity activity. Considerable difference exists between the physiological and movement demands of forwards and backs during competitive match play in Rugby League, especially in the frequency, duration, and distances associated with high-intensity locomotor activity. Simultaneous measurement of HR and movement patterns during match play revealed positional variation in the physiological demand of competition. Our results support the requirement of a high aerobic capacity for elite rugby league players, particularly for forwards who spend >50% of match-play performing activities at >85% HRmax.
Because of the large component of match play spent performing nonlocomotor high-intensity activities such as pulling, pushing, and tackling, a combination of GPS-accelerometer analysis technology and match video recordings may provide a greater insight into the determination and categorization of impact forces sustained and accelerations exerted during the frequent and varied contact elements of elite Rugby League match play. Further establishment of these collision-based variables and their influence on performance, fatigue, and recovery will permit appropriate training and recovery protocols to be established to optimize performance.
The author wishes to thank the players and staff of the Gold Coast Titans Rugby League Football Club, Australia, for participation and facilitation of this study. No grant aid was received in conjunction with this study, and no conflicts of interest are declared.
1. Bangsbo, J, Mohr, M, and Krustrup, P. Physical and metabolic demands of training and match-play in the elite football player. J Sports Sci
24: 665-674, 2006.
2. Barbero-Alvarez, JC, Coutts, A, Granda, J, Barbero-Alvarez, V, and Castagna, C. The validity and reliability of global positioning satellite system device to assess speed and repeated sprint ability (RSA) in athletes. J Sci Med Sport
13: 232-235, 2010.
3. Clark, LA. A comparison of the speed characteristics of elite rugby league players by grade and position. Strength Cond Coach
10: 2-12, 2003.
4. Coutts, A and Duffield, R. Validity and reliability of GPS
devices for measuring movement demands of team sports. J Sci Med Sport
11: 500-509, 2008.
5. Coutts, A, Reaburn, P, and Abt, G. Heart rate
, blood lactate concentration and estimated energy expenditure in a semi-professional rugby league team during a match: A case study. J Sports Sci
21: 97-103, 2003.
6. Cunniffe, B, Proctor, W, Baker, JS, and Davies, B. An evaluation of the physiological demands of elite rugby union using global positioning system tracking software. J Strength Cond Res
23: 1195-1203, 2009.
7. Deutsch, MU, Kearney, GA, and Rehrer, NJ. Time-motion analysis of professional rugby players during match play. J Sports Sci
25: 461-472, 2007.
8. Dobson, BP and Keogh, JW. Methodological issues for the application of time motion analysis research. Strength Cond J
29: 48-55, 2007.
9. Duthie, G, Pyne, D, and Hooper, S. The reliability of video based time motion analysis. J Hum Mov Stud
44: 259-272, 2003.
10. Edgecomb, SJ and Norton, KI. Comparison of global positioning and computer based tracking systems for measuring player movement distance during Australian Football. J Sci Med Sport
9: 25-32, 2006.
11. Esposito, F, Impellizzeri, F, Margonato, V, Vanni, R, Pizzini, G, and Veicsteinas, A. Validity of heart rate
as an indicator of aerobic demand during soccer activities in amateur soccer players. Eur J Appl Physiol
93: 167-172, 2004.
12. Gabbett, T, King, T, and Jenkins, D. Applied physiology of rugby league. Sports Med
38: 119-138, 2008.
13. Gastin, PB. Energy system interaction and relative contribution during maximal exercise. Sports Med
31: 725-741, 2001.
14. Hartwig, T, Naughton, G, and Searl, J. Defining the volume and intensity of sport participation in adolescent rugby union players. Int J Sports Phys Perform
3: 94-106, 2008.
15. King, T, Jenkins, DG, and Gabbett, TJ. A time motion analysis of professional rugby league match play. J Sports Sci
27: 213-219, 2009.
16. Larsson, P. Global positioning system and sport specific testing. Sports Med
33: 1093-1101, 2003.
17. MacLeod, H, Morris, J, Nevill, A, and Sunderland, C. The validity of a non-differential global positioning system for assessing player movement patterns in field hockey. J Sports Sci
27: 121-128, 2009.
18. MacLeod, H and Sunderland, C. Reliability and validity of a global positioning system for measuring movement patterns during field hockey. Med Sci Sport Exerc
39: S209-S210, 2007.
19. Meir, R, Arthur, D, and Forrest, M. Time and motion analysis of professional rugby league: A case study. Strength Cond Coach
1: 24-29, 1993.
20. Meir, R, Colla, P, and Milligan, C. Impact of the 10-meter rule change on professional rugby league: Implications for training. Strength Cond J
23: 42-46, 2001.
21. Petersen, C, Pyne, D, Portus, M, and Dawson, B. Validity and reliability of GPS
units to monitor cricket-specific movement patterns. Int J Sports Phys Perform
4: 381-393, 2009.
22. Rodriguez, FA and Iglesias, X. The energy cost of soccer: Telemetric oxygen uptake measurements versus heart rate
estimations. J Sports Sci
16: 484-485, 1998.
23. Schutz, Y and Herren, R. Assessment of speed of human locomotion using a differential satellite global positioning system. Med Sci Sport Exerc
32: 642-646, 2000.
24. Sirotic, AC, Coutts, AJ, Knowles, H, and Catterick, C. A comparison of match demands between elite and semi-elite rugby league competition. J Sports Sci
27: 203-211, 2009.
25. Sirotic, A, et al. Time-motion analysis of elite and semi-elite rugby league [abstract]. J Sci Med Sport
8: 67, 2005.
26. Spencer, M, et al. Time motion analysis of elite field hockey, with special reference to repeated-sprint activity. J Sports Sci
22: 843-850, 2004.
27. Toner, MM, Glickman, EL, and McArdle, WD. Cardiovascular adjustments to exercise distributed between the upper and lower body. Med Sci Sport Exerc
22: 773-778, 1990.
28. Townshend, AD, Worringham, CJ, and Stewart, IB. Assessment of speed and position during human locomotion using non-differential GPS
. Med Sci Sport Exerc
40: 124-132, 2008.
29. Wisbey, B, et al. Quantifying movement demands of AFL football using GPS
tracking. J Sci Med Sport
13: 531-536, 2010.
Keywords:© 2011 National Strength and Conditioning Association
GPS; contact sport; heart rate; monitoring