Objectives: The aim of this study was to assess the physiological responses to an intensified rugby league competition and explore the relationships between fatigue and match performance. Design: Prospective cohort study. Methods: Fifteen junior rugby league players (n = 8 forwards, 7 backs; mean ± SE, age 16.6 ± 0.2 years; body mass 81.6 ± 3.0 kg; and height 178.9 ± 1.8 cm) competed in five 40 min games over 5 days (two games each on days 1 and 2, one game on day 4, and no games on days 3 and 5). Over the competition, players performed a countermovement jump to assess neuromuscular fatigue, provided a fingertip blood sample to measure blood creatine kinase, and completed a questionnaire to monitor perceived wellbeing; ratings of perceived effort were recorded following each game. Global positioning system and video analysis of each game were used to assess match performance. Results: Over the first 3 days, there were progressive and large increases in neuromuscular fatigue which peaked 12 h after game 4 (forwards ES = 4.45, p = 0.014; backs ES = 3.62, p = 0.029), and muscle damage which peaked 1 h post game 4 (forwards ES = 4.45, p = 0.004; backs ES = 3.94 p = 0.012), as well as reductions in perceived wellbeing. These measures gradually recovered over the final 2 days of the competition. Compared to the backs, the forwards experienced greater increases in creatine kinase following game 2 (ES = 1.30) and game 4 (ES = 1.24) and reductions in perceived wellbeing (ES = 0.25-0.46). Match intensity, high-speed running, and repeated-high intensity effort bouts decreased in games 4 and 5 of the competition. Small to large associations were observed between the changes in fatigue, muscle damage and match performance, with significant correlations between creatine kinase and repeated high-intensity effort bout number (r = -0.70, p = 0.031) and frequency (r = 0.74, p = 0.002) and low-speed activity (r = -0.56, p = 0.029). Conclusions: Fatigue and muscle damage accumulate over an intensified competition, which is likely to contribute to reductions in high-intensity activities and work rates during competition.
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