Drop Jump Vertical Kinetics Identify Male Youth Soccer Players at Greater Risk of Non-contact Knee Injury

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.