Influence of an intensified competition on fatigue and match performance in junior rugby league players

Abstract

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. Prospective cohort study. Fifteen junior rugby league players (n=8 forwards, 7 backs; mean±SE, age 16.6±0.2 years; body mass 81.6±3.0kg; and height 178.9±1.8cm) competed in five 40min 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. Over the first 3 days, there were progressive and large increases in neuromuscular fatigue which peaked 12h after game 4 (forwards ES=4.45, p=0.014; backs ES=3.62, p=0.029), and muscle damage which peaked 1h 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). 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.