Association Football (soccer) is characterised by intermittent bouts of high-intensity activity interspersed with periods of low-to moderate-intensity exercise that places significant physical demands on players (Beato & Drust, 2021; Akenhead et al., 2016; Rampinini et al., 2011; Mohr et al., 2005, 2003). These match demands can lead to fatigue, defined as a symptom of tiredness or weakness underscored by complex physiological and psychological processes (Thomas et al., 2018). High-intensity match efforts can result in signs of fatigue, manifesting in altered neuromuscular and physical function and reduced perceived wellness, which can persist for at least 48 h (Cross et al., 2023; Hubbard et al., 2023; Brownstein et al., 2017; Thomas et al., 2017; Rampinini et al., 2011). This research project aimed to comprehensively understand the training effects in a professional academy soccer cohort.
Chapter 4 and Chapter 5 were focused on firstly determining the between-day reliability and sensitivity of neuromuscular, physical, perceptual, and cognitive function measures, alongside establishing the minimal detectable change (MDC) to identify the true change thresholds of each variable. All measures, except some athlete reported outcome measures (AROMs), displayed acceptable reliability (CV ≤ 10%). The MDC values for neuromuscular function (maximum voluntary contraction [MVC], 26 N; potentiated twitch force [Qtw,pot], 20 N; voluntary activation [VA], 1.6%) and physical performance (ten to five repeated jump test [10/5 RJT], 0.14 m.s-1; countermovement jump [CMJ], 3.3 cm) measures were calculated. The sensitivity findings (displaying a desired signal [change values] to noise [MDC] ratio of greater than one) revealed that MVC (–2.41 S:N ratio) and VA (–2.18), alongside perceptual muscle soreness (–1.32), were the most sensitive to training effects. Furthermore, potentiated twitch force (–0.83) and physical performance jump tests (10/5 RJT, –0.96; CMJ, –0.80) exhibited moderate sensitivity to training, showing S:N ratios close to one and reporting statistically significant training-induced responses. These findings offer practitioners valuable guidance for selecting reliable and sensitive measurement tools to assess training impact, and this range of neuromuscular, physical, and perceptual measures is recommended for implementation in applied soccer settings.
Chapter 6 explored in greater detail the training effects of a mixed-content standard training week. Neuromuscular, physical, and perceptual tests were carried out at before and after a strenuous training day, and at 24, 48, and 72 h post-session. The initial strenuous day and combined effects of two days training led to immediate alterations in neuromuscular function (MVC, pre to post-session a 11% reduction), both central (VA, 4%) and peripheral (Qtw,pot, 11%) in origin, lasting several days and persisting at 24 h (VA) and 72 h (MVC & Qtw,pot) post-strenuous training day. The substantial neuromuscular function impairments were mainly due to reductions in contractile function (peripheral mechanisms), highlighting the need for practitioners to focus restoring peripheral (skeletal muscle) function following intense exercise and match-play. These changes were accompanied by reductions in physical performance and increased levels of perceived muscle soreness. The MVC, Qtw,pot, VA, 10/5 RJT, and perceptual soreness all exhibited changes (signal) in response to training that exceeded the MDC (noise) of the testing tools, indicating true changes in performance. Therefore, it is recommended that these measurement tools be adopted in applied professional academy soccer settings.
In terms of seasonal variation of responses (early, mid, and late stages of the season; Chapter 7), the study found no interaction effect between stage of the season and response to training across a week for any measurement variable, suggesting the response to training in these players did not change over the course of a season. It implied a conformity in training response with negligible seasonal variation. However, an increase in neuromuscular function was evident from early- to mid-season (Qtw,pot & VA, P ≤ 0.05), followed by a drop in physical performance (10/5 RJT & CMJ; mid- to late-season, P ≤ 0.05) and VA (mid- to late-season, P ≤ 0.05) at the latter stages, indicating some chronic alterations as the season progressed. Caution was advised, as only VA measurements exceeded the MDC, with changes in other variables not large enough to confirm they surpassed the testing tool's inherent error.
In summary, academy soccer training resulted in substantial neuromuscular function impairment, with an accompanying impact on physical performance and perceptual wellness. These impairments acutely persisted for at least 72 hours post a strenuous training day, and this response was replicated at different stages of a season, indicating a conformity of training response. It is recommended that practitioners focus on developing their players as the season progresses with a comprehensive physical performance plan, to prepare players for the demanding academy programme. Furthermore, to formulate an effective weekly and season training plan that progresses and regresses the training load across different stages of the season and microcycle in response to player status, but as part of an overarching long-term development plan. It was also advised to implement appropriate recovery and regeneration modalities and procedures at optimal times during the training week and season phases, in conjunction with an efficient and insightful monitoring programme.