Objectives: To determine associations between drop-jump vertical kinetics and acute non-contact knee injury-risk in male youth soccer players. Design: Prospective cohort study. Setting: Professional soccer academies. Participants: Youth soccer players (n = 264). Main outcome measures: Drop-jump vertical kinetics; injury epidemiology. Associations between kinetics and injury were assessed using binary logistic regression. Differences between injured and uninjured groups were compared using statistical parametric mapping. Results: Peak braking: peak propulsive force ratio (OR = 1.59, 1.10-2.29, p < 0.05), propulsive work (OR = 0.53, 0.28-0.99, p < 0.05) and vertical stiffness (OR = 1.68, 1.13-2.52, p < 0.05) were associated with risk of sustaining a knee injury. All variables demonstrated `unusable` or `weak` levels of predictive ability in identifying players who would become injured (AUC 0.568-0.663). Conclusions: Drop-jump vertical kinetics that characterise the shape of the force-time waveform provide insight to acute non-contact knee injury-risk in male youth soccer players. Large transient spikes in force in the early phase of ground contact, coupled with reduced propulsive forces are a risk factor for acute non-contact knee injury in male youth soccer players. Variables are not sensitive enough to predict injury but provide additional training targets to help mitigate risk in this population. Highlights In this prospective study, male youth soccer players performed a baseline drop jump assessment. The prevalence of acute non-contact knee injury was 7% during the one playing season follow-up. Drop jump ground reaction force variables were unable to predict acute non-contact knee injury. Large impact force with reduced propulsive force is a risk factor for non-contact knee injury in male youth soccer players.
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