Weak Relationships between Stint Duration, Physical and Skilled Match Performance in Australian Football

ORIGINAL RESEARCH published: 23 October 2017 doi: 10.3389/fphys.2017.00820 Weak Relationships between Stint Duration, Physical and Skilled Match Performance in Australian Football David M. Corbett 1, 2 , Alice J. Sweeting 1, 2 and Sam Robertson 1, 2* 1 Institute of Sport, Exercise and Active Living, Victoria University, Melbourne, VIC, Australia, 2 Western Bulldogs Football Club, Melbourne, VIC, Australia Edited by: Billy Sperlich, Integrative & Experimentelle Trainingswissenschaft, Universität Würzburg, Germany Reviewed by: Giovanni Messina, University of Foggia, Italy Xiao Li, Shantou University Medical College, China *Correspondence: Sam Robertson Specialty section: This article was submitted to Exercise Physiology, a section of the journal Frontiers in Physiology Received: 13 July 2017 Accepted: 05 October 2017 Published: 23 October 2017 Citation: Corbett DM, Sweeting AJ and Robertson S (2017) Weak Relationships between Stint Duration, Physical and Skilled Match Performance in Australian Football. Front. Physiol. 8:820. doi: 10.3389/fphys.2017.00820 Frontiers in Physiology | www.frontiersin.org Australian Rules football comprises physical and skilled performance for more than 90 min of play. The cognitive and physiological fatigue experienced by participants during a match may reduce performance. Consequently, the length of time an athlete is on the field before being interchanged (known as a stint), is a key tactic which could maximize the skill and physical output of the Australian Rules athlete. This study developed two methods to quantify the relationship between athlete time on field, skilled and physical output. Professional male athletes (n = 39) from a single elite Australian Rules football club participated, with physical output quantified via player tracking systems across 22 competitive matches. Skilled output was calculated as the sum of involvements performed by each athlete, collected from a commercial statistics company. A random intercept and slope model was built to identify how a team and individuals respond to physical outputs and stint lengths. Stint duration (mins), high intensity running (speeds >14.4 km · hr−1 ) per minute, meterage per minute and very high intensity running (speeds >25 km·hr−1 ) per minute had some relationship with skilled involvements. However, none of these relationships were strong, and the direction of influence for each player was varied. Three conditional inference trees were computed to identify the extent to which combinations of physical parameters altered the anticipated skilled output of players. Meterage per minute, player, round number and duration were all related to player involvement. All methods had an average error of 10 to 11 involvements, per player per match. Therefore, other factors aside from physical parameters extracted from wearable technologies may be needed to explain skilled output within Australian Rules football matches. Keywords: performance analysis, sport statistics, classification tree, team sport, GPS INTRODUCTION Australian Football (AF) involves a high physical and skilled output for more than 90 min of play to maximize team performance (Gray and Jenkins, 2010). Physical and skill output may decline, as a function of time, during AF matches (Coutts et al., 2010). Consequently, a key tactical consideration during AF matches relates to the length of an on-field stint (i.e., the consecutive amount of time spent on ground by a player) for a player, before their physical and/or skilled output is adversely affected (Montgomery and Wisbey, 2016). In elite AF, there is a limitation on the number of player substitutions a team can make within a match. In the 2017 Australian Football League season, this 1 October 2017 | Volume 8 | Article 820 Corbett et al. Skill, Stint and Physical Performance differing combinations of dependent variables. This could allow examination of how physical and temporal parameters interact to influence skilled output. Utilizing a mixed analysis approach comprised of generalized linear mixed models and conditional inference trees, this study will; (i) identify how athlete skilled output changes as a function of time in an AF match, (ii) determine the extent to which these changes occur at the individual level, and (iii) reveal how different permutations of physical and skilled parameters might correspond to differences in skilled output. limit was 90 rotations per match. Consequently, it is crucial in AF that stints are not ended (or started) unnecessarily early, or are too short or long in duration. During an AF match, various athlete performance data is collected. Physical output can be measured via Global Positioning System (GPS) or Radio Frequency Identification (RFID) (Wyld, 2008; Coutts and Duffield, 2010). These devices typically sample at 10 or 15 Hz, allowing for the calculation of total distance (m), distance within velocity bands (i.e., distance covered >14.4 km·h−1 ), and peak velocity (km·h−1 ). Match statistics are provided by commercial performance analysis companies (Sullivan et al., 2014b). However, there is less standardization in the measurement of skilled output comparative to physical. Skilled output can be measured by quantifying the number of involvements or actions completed by each player. Involvements may include kicks, handballs and other actions considered important to match success by AF coaching staff. The amount of time each player spends on the field and on the bench is available as a measure of temporal output (Bradley and Noakes, 2013). Potentially due to a combination of cognitive (Tenenbaum and Bar-Eli, 1993) and physiological fatigue (Aughey, 2010), it is unlikely that players can maintain an optimal level of physical and skilled output for an entire match (Thelen and Smith, 1994; Aughey, 2010). In AF, a decrement in physical output has been observed for each quarter completed (Coutts et al., 2010), with a 3% reduction in meterage per minute for every 2 min spent on field during rotations longer than 5 min (Montgomery and Wisbey, 2016). Similarly, the level of skilled involvements for players also likely declines as the duration of a match increases. Recent research has examined how work rate, time on field and situational factors, including the number of stoppages, interact to affect skilled involvement (Sullivan et al., 2014a,b). Although factors influencing the skilled output of players have been identified to date (Sullivan et al., 2014a,b), research assessing how these factors may aid match-day stint/rotation strategies remains to be examined. Measures of skilled, physical and temporal output could be modeled to identify how the skilled output of a team and individual responds to change in temporal and physical output. For this purpose, generalized linear mixed models present a suitable analysis option, in that they allow for the quantification of independent and dependent variables with repeated measures (Gałecki (...truncated)