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Title: The effectiveness of fatigue monitoring in professional football
Author: Beattie, Catherine
ISNI:       0000 0004 9359 1793
Awarding Body: University of Bolton
Current Institution: University of Bolton
Date of Award: 2020
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Player monitoring is common practice in elite sporting environments for practitioners to gain an advantageous insight into the general fatigue and recovery status of athletes and has previously been investigated. However, the application and sensitivity of fatigue markers for elite football players are yet to be fully established. The physical demands of football have changed over time, with increases in both physical and technical parameters observed in recent years (Barnes et al., 2014; Bush et al., 2015). Higher physical demands, coupled with periods of fixture congestion require players to compete in up to three games per-week, and has resulted in an increased need to monitor the associated fatigue response to avoid performance decrements and the inherent risk of injury (Nedelec et al., 2012; Zouhal et al., 2013). Monitoring the impact of training and games on players’ physiological and physical responses can allow practitioners to make informed decisions to ensure athletes are at peak physical performance prior to the next fixture through training modification and/or adjustment of individual player’s recovery strategies. These markers of fatigue should be sensitive to both acute and chronic fluctuations in training/match load. Nevertheless, most research in elite football has been conducted over a short period in-season with limited observation of cumulative and chronic fatigue. Therefore, the primary aim of this thesis was to evaluate the sensitivity of conventional measures of fatigue (countermovement jump indices, creatine kinase concentrations and urine osmolality) on elite senior first team football players (now referred to as elite football players). The second aim was to assess whether these measures are sensitive to the stresses of an elite competitive football season. iii The aim of the first study (Chapter 4) was to examine the acute changes from 90-minutes (min) of competitive match-play in countermovement jump (CMJ), creatine kinase (CK) and urine osmolality (Uosm) scores as part of routine testing and monitoring of elite football players over the course of a season. The results indicated that CMJ height derived from a ‘Just Jump System’ (Just Jump System, Perform Better Limited, Southam, Warwickshire, UK) could detect significant impairments at 48-hours (h) post-match in physical performance after performing 90-min of competitive match play (-3.9 %, P = 0.014, ES = 0.37). However, the question was raised whether the impairment was a meaningful change in performance and/or of clinical significance. There were marked increases in CK concentration, measured via capillary blood, 24-h pre to 48-h post-match (41 %, P = 0.005, ES = -0.91), however post-match concentrations were low in comparison to the large reference range reported in literature and would suggest minimal muscular or fatigue related stress was present. Urine osmolality measured using a handheld urinary refractometer (Osmocheck pocket pal OSMO, Vitech Scientific Ltd, Japan) displayed no significant change 24-h pre to 48-h post-match reflecting that elite football players are able to achieve rehydration by 48-h post-game, or the equipment employed within the limitations of the research environment was not sensitive to changes. Chapter 5 mirrored that of Chapter 4 and used a more advanced assessment technique for physical performance via a force platform (HUR Labs Force Platform, Kokkola, Finland). Additional measures of physical performance (contraction time [CT], flight time [FT], the ratio between flight time and contraction time [FT:CT], peak power [PP], max force [MF], take-off velocity [TV], average power [AP], average force [AF]) were taken. This was due to research suggesting that concentric focused outputs from the ‘push-off’ phase of the jump, such as CMJ height, lacks the resolution to detect neuromuscular fatigue (NF) in elite athletes. The findings from this study demonstrated CMJ FT and AP (concentric based outputs) to be most sensitive to fatigue 48-h postmatch (-2.4 %, ES = -0.45 and -7.3 %, ES = -0.63, respectively) and moderately associated with external load parameters completed during 90-min of competitive matchplay (r = -0.40 to -0.50). Decrements were also noted in FT:CT (-7.4 %, ES = -0.39) reflecting changes to concentric push-off (FT) and altered movement strategy (CT), but was not sensitive to match external load. The output measures of CMJ height and TV also demonstrated sensitivity to detect signs of NF but CT, PP and MF did not. Creatine kinase concentrations at 48-h post-match showed no association to match external load but were sensitive to the overall demands of 90-min of competitive football (P = 0.001, ES = 0.66). Similar to the findings of Chapter 4, Uosm did not reveal any significant difference at 48-h post-match (P < 0.05). The position specific changes in these markers were as expected, showing the positon of central midfielder to display the greatest changes in CK and CMJ outputs likely attributable to their position covering the greatest total distance, high intensity running distance and number of high intensity actions. The studies comprising Chapter 4 and 5 show that CMJ testing and CK concentrations display particular promise as acute, simple, non-invasive assessments for monitoring the recovery-fatigue status of elite football players’ 48-h post-match. The aim of the third study (Chapter 6) was to examine the longitudinal fluctuations in the physiological and physical performance markers from Chapter 4 and 5 across a competitive season. To the author’s knowledge, this was the first study to address weekly variations in these measures over a competitive season. The results demonstrated large increases in CK concentration but minimal fluctuation over a competitive season [62 to 159 %, P < 0.05], and indicated that CMJ MF can be increased (5.1 to 7.0 %, P < 0.05) despite fluctuations in movement strategy focused outputs (TV, FT:CT and AP) possibly indicating low-level NF. Therefore, the results from this chapter support the idea that skilled performers’ are thought to exhibit greater movement variability to help achieve consistent performance outcomes. Hydration status measured via Uosm demonstrated significant increases to baseline over the season (30 to 84 %, P < 0.05), although the findings indicated that players were able to maintain a euhydrated state that would be unlikely to negatively affect performance output. Chapter 6 additionally provided 95 % reference ranges and normative values for the recovery-fatigue variables in this subgroup of elite football players to aid the interpretation of clinically meaningful changes from baseline. The aim of the last experimental Chapter (Chapter 7) was to observe the association between markers of training/match load and the conventional markers of recoveryfatigue over a competitive season, to determine the sensitivity of these markers to preceding and cumulative load. The high inter-individual variability in the recoveryfatigue variables was addressed by transforming raw scores into ‘Z-scores’ for the analysis. The results from regression analysis showed that the models used explained low proportions of variance in the physiological and physical performance parameters used (6 to 18 %). Creatine kinase had a weak positive association to cumulative match-time over the season and Uosm to the time-trend variable ‘match-week’ (week number of the season; P < 0.05). Match-week also demonstrated significant associations to increases in CMJ AF. Further, the results displayed weak, marginally significant, associations between CMJ CT and FT:CT to preceding match-load. All recovery-fatigue variables used demonstrated poor sensitivity to training load outputs measured via GPS over a season. The findings suggest that elite football players, who play regularly, demonstrate the capability to maintain physical output and be sufficiently recover by 24-h pre-match (for a Saturday fixture) despite a congested match schedule. The overall findings of this thesis have shown that simple output measures from a CMJ are able to detect impairments in physical performance and signs of NF 48-h post competitive match-play in elite football players. Further, concentric derived output measures from the ‘push-off’ phase previously criticised in research have displayed sensitivity to match external load. Across a competitive season, players are able to maintain MF and PP outputs despite signs of low-level NF via changes in ‘jump-strategy’ (e.g. TV, FT:CT and AP). Creatine kinase, although sensitive to overall match-play, displays changes of minimal clinical significance 48-h post-match. However, CK did demonstrate sensitivity to cumulative match-min played across the season. Therefore, if interpreted correctly CK concentrations may provide practitioners with insights into cumulative fatigue/muscular stress. Incorporating additional biomarkers may further enhance detection of physiological and physical stress related changes to match and training demands. Lastly, the monitoring of hydration status via Uosm reflects that players are able to maintain a state of euhydration across a season but shows no associations to preceding match or training demands, perhaps a limitation of the equipment employed in the research environment was not sensitive to changes. Therefore, monitoring for spikes in CK concentrations and impairments in CMJ performance, when interpreted correctly, may provide clinically relevant insights of individual players prior to the next training session and/or fixture, ultimately equipping practitioners with an advantageous knowledge concerning recovery-fatigue status.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available