Is limb asymmetry an intrinsic risk factor for time-loss groin injury in professional male soccer players?

Objectives: To provide normative values for between-limb asymmetry of hip strength and range of motion (ROM) in professional male soccer players and evaluate the relationship between these asymmetries and groin injury. Design: Secondary analysis of a prospective cohort study. Methods: A total of 438 professional male soccer players underwent musculoskeletal screening, injury and exposure surveillance over two consecutive seasons. Between-limb asymmetry for two hip strength (eccentric adduction and abduction) and six ROM measures were calculated, and normal asymmetry considered within 1 standard deviation (SD) of the mean. Cox proportional hazard regression analysis estimated the association between asymmetry and time-loss groin injury. Results: Normal asymmetry ranged between 0.3% and 27.3% across strength and ROM variables. No association was found between groin injuries and asymmetry in eccentric hip adduction (HR = 0.99, 95%CI = 0.98-1.00; p = 0.167) or abduction strength (HR = 1.00, 95%CI = 0.99-1.01; p = 0.745). For five of the six ROM measures, no association with groin injuries were determined. A statistically significant, though likely clinically irrelevant, association was found between groin injury and dominant leg total hip rotation ROM (HR = 1.03, 95% CI = 1.00-1.05; p = 0.040). Conclusion: Normal hip strength and ROM asymmetry ranged between -27 and +20%. No clinically relevant associations were found between asymmetry in hip strength or ROM and time-loss groin injuries. Level of evidence: 2.