Strength deficits of the hamstrings following surgery on the anterior cruciate ligament: a case-control ­study of elite alpine ski racers

Background: Research to date clearly shows that injuries to the cruciate ligaments are a frequent occurrence in alpine ski racing. The hamstrings play an important role in protecting the anterior cruciate ligament (ACL). Here eccentric muscle activity, in particular, is of great significance as it plays a more important role in terms of duration and intensity than concentric muscle activity in alpine ski racing. The aim of this study was to establish whether the hamstrings of alpine ski racers show eccentric strength deficits following surgery on the anterior cruciate ligament. Methods: A case-control study was performed with athletes who had undergone surgery on the anterior cruciate ligament 49 ± 41 months previously and healthy ski racers. The total eccentric strength of both legs measured in the hamstrings supporting the ACL (n=18) was compared with the healthy group (n=70); the strength of the operated leg was also compared with the healthy leg and with the mean for the healthy group. Eccentric strength was measured during the Nordic hamstrings exercise performed on the NordBord hamstring testing system. Group comparisons were performed using ANOVA and Bonferroni Post-hoc analyses. Multiple linear regressions were used to assess the relevant independent variables explaining total eccentric strength and Limb Symmetry Index. Results: The relative total eccentric strength of both legs in the hamstrings of the ACL group was significantly lower than in the healthy group (p=0.031). In addition, the relative eccentric strength of the operated leg was significantly lower compared to the healthy group (p=0.024). Leg asymmetry was also significantly greater in athletes who had undergone surgery on one leg (p=0.016) than in healthy subjects and athletes who had undergone surgery on both legs. 56% of the total eccentric strength of both legs could be explained by surgery, age and gender. 18% of the leg asymmetry was explained by the variables surgery, total eccentric strength of both legs and height. Conclusion: Several years after anterior cruciate ligament surgery, ski racers still have deficits in terms of the eccentric strength of their hamstrings compared with healthy ski racers. Therefore more attention should be paid during rehabilitation to the eccentric strength of the hamstrings with a view to strengthening and testing them. Measurement using the NordBord system is suitable for routine monitoring of eccentric strength. Further studies are needed to improve understanding of the influence of hamstrings strength on cruciate ligament injuries.