INTRODUCTION: Elite junior Australian football players experience high loads across levels of competition and training [1]. High loads have been linked to the risk of injury, either in a linear or curvilinear (U-or J-curve) fashion [2]. Few studies have adjusted for variables that may influence the load-injury relationship such as how well players respond or cope with the physical and mental stresses of their sport [3]. The purpose of this study was to investigate the relationships between player load, wellness and injury. We hypothesised that player wellness would mediate and/or moderate the load-injury relationship. METHODS: Data were collected and analysed from 280 Australian football players from nine under-18 state league clubs across one season. Internal load was measured via session rating of perceived exertion (sRPE) for training and competition. Week and month-based absolute and relative load measures were then calculated. Player wellness was reported three times per week for sleep duration and ratings (1-5) of sleep quality, fatigue, soreness, stress and mood. Principal Component Analysis factor loadings were used to identify distinct covariates (6 components, 17 load and wellness variables). Injury was defined as `any injury leading to a missed training session or competitive match`, with only new injuries included in the analysis. Associations between covariates and injury risk (yes/no) were determined via logistic Generalised Estimating Equations. RESULTS: Univariate analysis indicated that load was associated with injury in the form of a non-linear relationship. Further, wellness as a composite measure, as well as individual factors of stress, soreness and fatigue demonstrated direct relationships with injury. Modelling indicated evidence of mediation where increased soreness amplified the relationship between stress and injury, while increased sleep duration reduced the relationship. A significant interaction term between load and wellness on injury was found (OR= 0.76 95% CI 0.62 to 0.92, P<0.01), indicating the regression weight of load on injury varied as a function of wellness (i.e., wellness acting as a moderator, with poor wellness at high loads further increasing the risk of injury). Including wellness as a mediator or moderator in the analysis suggests that injury risk increases substantially at a 1-week load of 3750 au and beyond. CONCLUSION: Internal measures of training and competition load are associated with injury risk. This relationship is further influenced by player subjective wellness and sleep, which when poor can amplify the risk of injury at high loads. There is also evidence that higher stress is linked with injury and that soreness and sleep can mediate this relationship. Efforts to monitor and manage load and to support positive adaptive responses may reduce the risk of injury, with perceptions of stress, soreness and sleep relevant in this cohort.
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