Progressive submaximal effort hamstring muscle endurance is reduced after reconstruction of the anterior cruciate ligament

Background: Endurance capability in the muscles controlling the knee is poorly understood post anterior cruciate ligament (ACL) reconstruction, despite many sporting activities requiring notable muscle endurance. The hamstring muscles, when active, provide important anatomical support to protect the reconstructed graft. In the absence of good hamstring endurance, fatigue may predispose individuals to re-injury. Objective: To assess whether ACL reconstruction (ACLR) with a hamstring graft leads to reduced hamstring endurance 9-13 months post-surgery. Study design: A cross-sectional inter-limb comparison study was undertaken with participants 9-13 months after an ACLR with a hamstring graft, and a group of age, sex, and activity-matched controls. There were 22 participants in each group. Method: Submaximal hamstring endurance was measured using a progressive fatigue test on an isokinetic dynamometer at a joint angular velocity of 120/second. The dependant variable was the maximum number of repetitions performed. Statistical comparisons were made across injured, uninjured and control group limbs. Results: There was a significant (p < 0.05) deficit in hamstring endurance observed between the injured leg (mean: 111 repetitions, SD 49) and uninjured leg (mean: 136 repetitions, SD 67) of the ACL group, but not between the uninjured and control group legs (mean: 124 repetitions, SD 50). Conclusion: The 18% deficit in submaximal hamstring endurance across the ACL-reconstructed individual's limbs is indicative of a notable loss in muscle performance at 9-13 months post-surgery. These results provide initial evidence for supporting further research examining the inclusion of hamstring endurance training in ACL rehabilitation programmes post-surgery.