Objectives To examine the within- and cross-season neuromuscular fatigue responses in English Premier League U-18 academy football players. Design Twenty-five players from the same team completed weekly countermovement jump and isometric adductor and posterior chain strength tests for a full competitive season. Methods Global positioning system measures of training and match total, high-metabolic load and sprint distance were recorded daily and converted into exponentially weighted moving average seven- and twenty-eight-day values. Results TD28 (p<.001), HML28 (p<.001), and SD28 (p=.002) shared negative relationships with countermovement jump height, but there was no main cross-season effect (p=.137). TD28 (p=.016) and HML28 (p=.012) positively related to isometric posterior chain strength but there was no effect of SD28 (p=.653), SD7 (p=.549), TD7 (p=.080) or HML7 (p=.104). Cross season, isometric posterior chain strength followed a curvilinear response whereby performance increased across the beginning of the season and decreased towards the end of the season (p=.003). There was no effect of training load or time on isometric adductor strength performance (p>.094). Conclusions Neuromuscular status, signalled by countermovement jump height changes fluctuates across the season in response to sustained changes in training and match load, but there is no evidence of a main cross-season linear effect. Total training and match volume exert moderating effects on the internal training load dose, and in-turn, important moderating effects on neuromuscular fatigue, particularly when composed of high volumes of high-intensity and sprint distances. The posterior chain might be particularly susceptible to fatigue towards the end of the season.
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