Abstract
ObjectiveTarget trial emulation is a framework for conducting causal inference using observational data. We employ this framework to estimate the effect of changing planned participation duration, measured using the acute:chronic workload ratio (ACWR), on injury risk among adolescent ice hockey players without recent injuries. DesignProspective cohort study designed to emulate a hypothetical randomized trial. MethodsWe used data from a 5-year cohort study (2013–2018) of ice hockey players aged 13 to 17 years in Alberta and British Columbia. We estimated injury risks associated with different planned changes in hockey participation duration (e.g. half [ACWR = 0.5], no change [ACWR = 1], two-fold [ACWR = 2], three-fold [ACWR = 3], and five-fold [ACWR = 5]) relative to participation in the previous 4 weeks. Outcomes were modeled using generalized additive models. We conducted secondary analyses restricted to concussions, and stratified by league bodychecking status. ResultsThere were 2633 eligible participants, contributing 115,821 player-trials. Injury risk was 1.9 % (95 % CI: 1.7 %–2.3 %) for no change in participation (ACWR = 1). Injury risk ratios (RRs) were 0.43 at ACWR = 0.5 (95 % CI: 0.31–0.54), 1.62 (95 % CI: 1.33–1.98) at ACWR = 2, 1.91 at ACWR = 3 (95 % CI: 1.52–2.48) and 2.35 at ACWR = 5 (95 % CI: 1.68–3.26). Patterns were similar by league bodychecking status. Concussion RRs were stable between ACWR = 1 to 1.5, but RRs were greater than for any injury past ACWR = 2. ConclusionWithin the assumptions of this target trial emulation, injury risk increases consistently (no sweet spots) for increases in planned changes in participation duration relative to the previous 4 weeks among adolescent ice hockey players without recent injuries. Injuries in injury risk are less than expected for the increased exposure time at risk, suggesting beneficial effects of increasing participation that partially counteract the increased exposure time.
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