The influence of injury history on countermovement jump performance and movement strategy in professional soccer players: implications for profiling and rehabilitation foci.

Context: Professional soccer players who have sustained a lower limb injury are up to 3x more likely to suffer a re-injury, often of increased severity. Previous injury has been shown to induce compensatory strategies during neuromuscular screening tests, which might mask deficits and lead to misinterpretation of readiness to play based on task outcome measures. Objective: To investigate the influence of previous injury in professional soccer players on countermovement jump (CMJ) performance and movement strategy. Design: Cross-sectional. Setting: Professional soccer club competing in the English Championship (tier 2). Patients (or other Participants): Outfield players with a minimum 6 years as a professional. Intervention(s): Players were categorised as previously injured (n=10) or not injured (n=10). All players completed double and single leg CMJ trials. Main Outcome Measures: CMJ performance was quantified as jump height and flight time:contraction time ratio. CMJ movement strategy was quantified as force-time history differentiating eccentric and concentric phases, and CMJ depth. Results: Double leg CMJ was not sensitive to previous injury in performance or movement strategy. In contrast, single leg CMJ performance was impaired in players with previous injury who generated significantly lower eccentric and concentric peak force and rate of force development, and a deeper countermovement. Impaired single CMJ performance was also evident in the non-affected limb of previously injured players, suggesting cross contamination. Hierarchical ordering revealed that the eccentric phase of the CMJ contributed little to performance in previously injured players. In non-injured players, eccentric rate of force development and concentric peak force were able to account for up to 89% of the variation in CMJ performance. Conclusions: Single leg CMJ is advocated for player profiling, being more sensitive to previous injury and negating the opportunity for inter-limb compensation strategies. Movement strategy deficits in previously injured players suggest rehabilitation foci specific to eccentric force development.