Eccentric hamstring strength deficit and poor hamstring-to-quadriceps ratio are risk factors for hamstring strain injury in football: A prospective study of 146 professional players

Objectives: The purpose of this study was to investigate whether preseason isokinetic strength measures were predictive of future HSI among professional football players. Design: Prospective cohort study, Level of evidence 2. Methods: A total of 169 professional players participated in a preseason isokinetic strength screening, followed by a 10-month competitive season. Testing protocol included the concentric performance of both knee flexion and extension at 60 deg s−1 and 240 deg s−1 and the eccentric performance of the knee flexor at 30 deg s−1. Strength deficits, bilateral differences, and hamstring to quadriceps strength ratios were computed. Univariate and multivariate logistic regressions were used to identify potential risk factors of HSI. Receiver operating characteristic (ROC) curves were used to investigate the sensitivity and specificity of the strength measures. Results: Forty-one acute HSIs were sustained, and 12% (n = 5) reoccurred within the study period. In the multivariate analysis, we have shown an association between the injury risk and eccentric hamstring peak torque below 2.4 N m kg−1 (OR = 5.59; 95% CI, 2.20–12.92); concentric H/Q ratio below 50.5% (OR = 3.14; 95% CI, 1.37–2.22); players with previous injury of HSI (OR = 3.57; 95% CI, 3.13–8.62). ROC analysis displayed an area under curve (AUC) of 0.77, indicating fair combined sensitivity and specificity of the overall predicting model. Conclusions: Professional football players with significant lower isokinetic hamstring strength, lower hamstring-to-quadriceps strength ratio, and a previous injury of HSI were linked to an increased risk of acute HSI.