Evolution of Physical Demands of Australian Football League Matches from 2005 to 2017: a Systematic Review and Meta-Regression Samuel J
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Janetzki et al. Sports Medicine - Open (2021) 7:28 https://doi.org/10.1186/s40798-021-00301-1 SYSTEMATIC REVIEW Open Access Evolution of Physical Demands of Australian Football League Matches from 2005 to 2017: A Systematic Review and Meta-Regression Samuel J. Janetzki1* , Pitre C. Bourdon1, Kevin I. Norton1, Jackson C. Lane1 and Clint R. Bellenger1,2 Abstract Background: There is extensive research investigating the match demands of players in the Australian Football League (AFL). Objective: This systematic literature review and meta-regression sought to analyse the evolution of in-game demands in AFL matches from 2005 to 2017, focusing on the relationship between volume and intensity. Methods: A systematic search of Ovid MEDLINE, Embase, Emcare, Scopus, SPORTDiscus, and Cochrane Library databases was conducted. Included studies examined the physical demands of AFL matches utilising global positioning system (GPS) technology. Meta-regression analysed the shift in reported volume (total distance and total match time) and intensity (metres per minute [m.min−1], sprint duration and acceleration) metrics for overall changes, across quarters and positional groups (forwards, nomadics and defenders) from 2005 to 2017 inclusive and for each year between 2005 and 2007, 2007 and 2010, 2010 and 2012, and 2012 and 2015/2017 breakpoints. Results: Distance (p = 0.094), m.min−1 (p = 0.494), match time (p = 0.591), time over 18 km·h−1 (p=0.271), and number of accelerations greater than 4 km·h−1 (p=0.498) and 10 km·h−1 (p=0.335) in 1 s did not change from 2005 to 2017. From 2005 to 2007 volume decreased (− 6.10 min of match time; p = 0.010) and intensity increased (6.8 m.min−1 increase; p = 0.023). Volume and intensity increased from 2007 to 2010, evidenced by increases in total distance (302 m; p = 0.039), time over 18 km·h−1 (0.31 min; p = 0.005), and number of accelerations greater than 4 km·h−1 (41.1; p = 0.004) and 10 km·h−1 (3.6; p = 0.005) in 1 s. From 2010 to 2012, intensity decreased, evidenced by reductions in metres per minute (− 4.3; p = 0.022), time over 18 km·h−1 (− 0.93 min; p < 0.001), and number of accelerations greater than 4 km·h−1 (− 104.4; p < 0.001) and 10 km·h−1 (− 8.3; p < 0.001) in 1 s, whilst volume stabilised with no changes in distance (p = 0.068) and match time (p = 0.443). From 2012 to 2015/2017 volume remained stable and intensity increased with time over 18 km·h−1 (0.27 min; p=0.008) and number of accelerations greater than 4 km·h−1 (31.6; p = 0.016) in 1 s increasing. (Continued on next page) * Correspondence: [email protected] 1Alliance for Research in Exercise, Nutrition and Activity (ARENA), University of South Australia, GPO Box 2471, Adelaide, South Australia 5001, Australia Full list of author information is available at the end of the article © The Author(s). 2021 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. Janetzki et al. Sports Medicine - Open (2021) 7:28 Page 2 of 21 (Continued from previous page) Conclusions: Changes in volume and intensity of AFL match demands are defined by discrete periods from 2007 to 2010 and 2010 to 2012. The interaction of rule and interpretation changes and coaching strategies play a major role in these evolutionary changes. In turn, modified game styles impact player game demands, training, and selection priorities. Standardisation and uniformity of GPS data reporting is recommended due to inconsistencies in the literature. Keywords: Australian Football League (AFL), global positioning system (GPS), match demands Key Points sports, AF has evolved over time [13, 14] with improve- ments in player athleticism, club, staff and player profes- Changes in the volume and intensity of AFL match sionalism, and rule changes contributing significantly to demands from 2005 to 2017 are defined by discrete, the evolution of elite AF [14, 15]. In comparison to their evolutionary periods from 2007 to 2010 and 2010 to late 1990 counterparts, modern day AF players are re- 2012. Forwards exhibited the greatest change in quired to engage in more frequent, high intensity sprint volume and intensity of any positional group across efforts for longer periods of time [7], with the ability to these periods. recover from these intermittent, high intensity activities Rule changes, professionalism of the sport and being a defining characteristic of the modern, elite AF players, and the evolution of game style are player [16]. postulated as the driving factors behind changes to Professional sport’s development more broadly has the match demands of elite AFL players. been characterised by the rapid evolution of game inten- Standardisation and uniformity are recommended sity and player demands [17–21]. With elite AF being a for the manner and form in which AFL GPS match multi-billion-dollar industry and the players being the data are reported, particularly in relation to high- primary asset, it is essential AFL clubs have a compre- speed running metrics. hensive understanding of individual player and team movement patterns, with the goal of maximising player Introduction and team performance [14]. Australian rules football (AF) is a contact team sport The introduction of GPS technology to the AFL in played between two teams of 22 players, with 18 players 2005 provided clubs with the ability to more accur- permitted on the field at any one time and four players ately monitor and understand their players’ in-game on the interchange bench. Teams can utilise up to 90 movement patterns [7]. Quantifying game trends aids player interchanges per match. The aim of competing the optimisation of player preparation for matches by teams is to score more points than the opposition team informing training drills and developing fitness pro- over four, 20-minute quarters of match play plus time files suited to high-performance AF, as well as help on [1]. The playing surface area varies considerably be- predict future game demands and assist in player se- tween grounds; however, the playing surface of the Mel- lection. This led to significant growth in the literature bourne Cricket Ground is approximately 80% larger investigating the match demands of AFL players [7, than the biggest international standard soccer pitch. At 22, 23]. Studies have more recently examined the re- the end of the first and third quarters, players are lationship between in-game running demands on indi- afforded a 6-minute rest period, with a 20-minute rest vidual and team match performance [24], as well as period at half-time. Currently in 2020, 18 professional the influence of individual player characteristics such teams compete in the Australian Football League (AFL), as player calibre [24, 25], experience [26], fitness [27] the premier AF competition. and the number of interchange rotations [28, 29]on AF is regarded as a physically and technically demand- match running performance. There has also been ing sport [2–5]. The physical demands of an AF match consideration of match-related factors on physical vary considerably between playing positions [6], with output such as team success [24] and ladder position global positioning system (GPS) analysis revealing [30], opposition strength [31], number of stoppages players typically cover 11,000 to 17,000 metres during a [31], match location (home or away) [31]andtimeof match [7–9]. Historically, AF players were estimated to match during the season [4, 31]. spend 60 to 90% of a match engaging in low intensity Measuring speed and acceleration data are important activities (e.g. walking and jogging), largely dependent to understand the demands of field-sport athletes like on playing position and the method of player analysis AF players [32]. Studies analysing the application of GPS utilised [10–12]. However, like most field-based team technology in AFL matches suggest there are many Janetzki et al. Sports Medicine - Open (2021) 7:28 Page 3 of 21 factors attributable to the variation in match activity profil* or total distance? or HSR or high speed run- profiles of elite AF players. Importantly, recent improve- ning or high-speed running or sprint* or duration ments in the validity and reliability of GPS units [33–35] or meter* per minute* or metre* per minute* or permits greater precision of the match analysis data [36], meter?-per-minute? or metre?-per-minute? or phys- however the reliability of movement data collected at ical* condition* or endurance or high-intensity speeds in excess of 20 km·h-1 remains in question [33]. interval train* or accelerat* or fitness Despite the myriad of studies which have quantified and investigated the match demands of elite AF, there is Eligibility criteria minimal longitudinal evidence supporting the anecdotal Studies were eligible for inclusion in this review if their increase in the intensity of modern AF matches.