Defining and quantifying fatigue in the rugby codes

PLOS ONE RESEARCH ARTICLE Defining and quantifying fatigue in the rugby codes Mitchell Naughton1,2,3, Tannath Scott4,5, Dan Weaving ID4*, Colin Solomon1,2, Scott McLean2 a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 1 School of Health and Behavioural Sciences, University of the Sunshine Coast, Sippy Downs, Queensland, Australia, 2 Centre for Human Factors and Sociotechnical Systems, University of the Sunshine Coast, Sippy Downs, Queensland, Australia, 3 Applied Sports Science and Exercise Testing Laboratory, University of Newcastle, Ourimbah, New South Wales, Australia, 4 Carnegie Applied Rugby Research Centre, Leeds Beckett University, Leeds, West Yorkshire, United Kingdom, 5 School of Health Sciences and Social Work, Griffith University, Gold Coast, Queensland, Australia * Abstract OPEN ACCESS Citation: Naughton M, Scott T, Weaving D, Solomon C, McLean S (2023) Defining and quantifying fatigue in the rugby codes. PLoS ONE 18(3): e0282390. https://doi.org/10.1371/journal. pone.0282390 Editor: Emiliano Cè, Universita degli Studi di Milano, ITALY Received: October 13, 2022 Accepted: February 13, 2023 Published: March 10, 2023 Peer Review History: PLOS recognizes the benefits of transparency in the peer review process; therefore, we enable the publication of all of the content of peer review and author responses alongside final, published articles. The editorial history of this article is available here: https://doi.org/10.1371/journal.pone.0282390 Copyright: © 2023 Naughton et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All data is included either in the figures and tables within the paper, or in the Supporting information documents attached. The rugby codes (i.e., rugby union, rugby league, rugby sevens [termed ‘rugby’]) are teamsports that impose multiple complex physical, perceptual, and technical demands on players which leads to substantial player fatigue post-match. In the post-match period, fatigue manifests through multiple domains and negatively influences recovery. There is, however, currently no definition of fatigue contextualised to the unique characteristics of rugby (e.g., locomotor and collision loads). Similarly, the methods and metrics which practitioners consider when quantifying the components of post-match fatigue and subsequent recovery are not known. The aims of this study were to develop a definition of fatigue in rugby, to determine agreement with this common definition of fatigue, and to outline which methods and metrics are considered important and feasible to implement to quantify post-match fatigue. Subject matter experts (SME) undertook a two-round online Delphi questionnaire (round one; n = 42, round two; n = 23). SME responses in round one were analysed to derive a definition of fatigue, which after discussion and agreement by the investigators, obtained 96% agreement in round two. The SME agreed that fatigue in rugby refers to a reduction in performance-related task ability which is underpinned by time-dependent negative changes within and between cognitive, neuromuscular, perceptual, physiological, emotional, and technical/tactical domains. Further, there were 33 items in the neuromuscular performance, cardio-autonomic, or self-report domains achieved consensus for importance and/or feasibility to implement. Highly rated methods and metrics included countermovement jump force/power (neuromuscular performance), heart rate variability (cardio-autonomic measures), and soreness, mood, stress, and sleep quality (self-reported assessments). A monitoring system including highly-rated fatigue monitoring objective and subjective methods and metrics in rugby is presented. Practical recommendations of objective and subjective measures, and broader considerations for testing and analysing the resulting data in relation to monitoring fatigue are provided. Funding: The author(s) received no specific funding for this work. PLOS ONE | https://doi.org/10.1371/journal.pone.0282390 March 10, 2023 1 / 17 PLOS ONE Competing interests: The authors have declared that no competing interests exist. Defining and quantifying fatigue in rugby Introduction The rugby codes (i.e., rugby union, rugby league, rugby sevens [hereafter termed ‘rugby’]) are team-sports that impose multiple complex physical, perceptual, and technical demands on players. In rugby, there has been a proliferation of methods and metrics to quantify and monitor each specific component of training and match-play through technologies such as global positioning systems (GPS), accelerometers, and heart-rate telemetry to quantify the output of the player on the field. For example, the frequency, intensity, and duration of locomotor and collision actions (termed the external load), and the players psycho-physiological responses (termed the internal load) to the completed external loads [1–3]. In addition to improved quantification of match and training external and internal loads, there has been an increased recognition of the fatiguing effects of elevated match-related external and internal loads, and the negative impact of the associated fatigue may have on recovery into the subsequent training week [4, 5]. Aben et al. [4] identified that match-play contributed to a decrease in lower-body power of up to ~31%, an increase of the muscle damage biomarker creatine kinase (CK) of up to ~450%, as well as negative disturbances to mood, and testosterone and cortisol [4]. From a player fatigue perspective, these negative changes did not typically return to pre-match baseline levels until 48–72 hours post-match [4, 6]. Post-match fatigue is multidimensional [7], and can be quantified by objective (e.g. neuromuscular performance, cardio-autonomic, tissue biomarker tests etc.) and subjective (e.g. selfreported soreness, fatigue, mood etc.) methods and metrics [6, 8]. During the competitive season, the deleterious effects of fatigue decrease the player’s readiness to train within the constraints of the typical week to week match-play microcycle. Pre- and post-match monitoring of each player’s fatigue state is therefore important in the in-season period to identify if players are or are not returning to their individual baseline state between matches [9]. For support staff, this necessitates applying monitoring systems that quantify and integrate the various dimensions of fatigue, and the subsequent recovery process. This can then inform decision support systems to maintain or adjust training prescription (e.g., frequency, intensity, duration), and/or implement additional or specific recovery interventions [10–12]. Whilst the importance of quantifying training and competition loads and fatigue in rugby has been established [13], there have been limitations in prio (...truncated)