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What did I do? Aims of your PhD
As a ‘real-world’, coach/management-directed question, my aim was to establish the ‘performance readiness’ of players competing in the English Premier League (EPL) in attempt to reduce injury/illness risk and maximise player availability and performance. The primary focus of my thesis was to evaluate potential indicators of fatigue which may be easily monitored and used in an EPL environment. My first study established the reliability of such parameters, and second, third and fourth investigations explored the sensitivity to changes in daily and acute training load and during typical competitive weeks, respectively.
Why did I do it? Rationale for your PhD
The acute and chronic physical demands of football players competing in the EPL have significantly increased in recent years.1 Consequently, adapting training load prescription and maximising recovery interventions for players may contribute to reducing injury and illness risk and even enhance physical and mental performance.2 Therefore, evaluation and quantification of player physiological/fatigue response may provide beneficial information to key stakeholders including the player, technical coaches/management, medical and sports science personnel involved in player health and performance.
How did I do it? Brief overview of main methods
Over the course of four competitive seasons, training/match load and morning-measured fatigue variables were collected in EPL players from the same team.
Determining the reliability, minimal clinically important difference and sample size estimation of potential fatigue measures
Field-based reliability estimates are required to quantify meaningful changes in any performance measure across time periods that are typically used to quantify the effects of any intervention3 within the players normal training environment. Potential fatigue measures were collected from a cohort of EPL players on two separate occasions, 1 day apart and free from any training intervention. Minimum clinically/practically important difference calculations were used to predict sample size requirements which allowed us to understand which measures were suitable to track changes in load in future investigations.
Determining the sensitivity of fatigue measures
Decisions regarding player training status are required on a daily basis in elite football environments. Therefore, relationships between daily training load and the subsequent days morning-measured fatigue variables were investigated during a typical competitive period. Players may also subjectively report ‘fatigue’ following a number of training days or matches during a short period; therefore, sensitivity of fatigue measures was also compared with the training load accumulated over the previous 2, 3 or 4 days during a similar competitive phase. The final investigation was to quantify the mean daily changes in training load and parallel changes in fatigue measures across in-season training weeks in EPL players.
What did I find? Overview of main findings
In the first study, athlete self-report measures (fatigue, sleep, muscle soreness), countermovement jump height, submaximal heart rate, heart rate recovery (HRR and HRR%) and heart rate variability (HRV) demonstrated good reliability with the absence of statistical bias. Sample size estimations derived from the minimal clinically important difference indicated that these measures could be applied within feasible squad sizes typically observed in elite soccer, therefore applicable for future experimental work.
The results of the second study showed perceived fatigue and HRV were sensitive to daily changes in training load (total high-speed running distance) in EPL players.4 In the third study, perceived ratings of fatigue were significantly correlated to short-term load accumulation (1–4 days), respectively.5 These findings demonstrate that athlete self-report measures, particularly perceived fatigue was significantly sensitive to daily and short-term training load accumulation. The sensitivity of all other fatigue markers to changes in training load was not improved when compared with training loads beyond the previous days training, although small changes in submaximal heart rate over 4-day acute training load were observed. Finally, in the fourth investigation, all athlete self-report measures (fatigue, sleep, muscle soreness), but not heart rate response indices, were found to fluctuate across competitive weeks in parallel with training load.6
What is the most important clinical impact/practical application?
Simple athlete self-report measures are reliable and sensitive to short training and competition phases and thus may be a suitable strategy for practitioners to use in the attempt to establish fatigue status in elite soccer players. Other measures of fatigue (heart rate response and countermovement jumps) may be more sensitive to varying types and dose of training load. The quantification of player fatigue status may assist multidepartmental processes such as performance recovery and training preparation and guide coaches/managers in their training prescription and scheduling figure 1.
I acknowledge with sincere gratitude Professor Warren Gregson, Professor Greg Atkinson, Professor Barry Drust, Professor Martin Buchheit and Dr Tony Strudwick. I also thank the management and in particular Sir Alex Ferguson, the coaching staff, players and science and medicine staff at Manchester United Football Club.
Funding This study was funded by Manchester United Football Club as part of research collaboration with Liverpool John Moores University.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
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