Purpose: To analyse possible discrepancies in the recovery of hamstring muscle strength between concentric and eccentric testing during the first year of rehabilitation among patients treated with an anterior cruciate ligament reconstruction with an hamstring autograft.

Method: The study was performed as a prospective, observational register study. Cross-sectional data from 10 weeks, 4-, 8-and 12 months after anterior cruciate ligament reconstruction were extracted from a rehabilitation outcome register between February 2018 and February 2021. Included patients performed an isokinetic concentric test in the Biodex and an eccentric test in the NordBord. Primary outcome was limb symmetry index for hamstrings strength for respective tests.

Results: A total of 113 patients (50 women and 63 men) were included in the study. The included patients had an average age of 25.2 ± 8.0 years with a range of 15–52 years. There were a total of 27 patients at 10 week, 41 patients at 4 months, 41 patients at 8 months and 41 patients at 12 months. There were statistic significant differences in the recovery of hamstring muscle strength at all timepoints between the tests with clinically significant difference at 10 weeks, 4-and 8 months.

Conclusion: Study findings demonstrated a remaining deficit in limb symmetry index assessed eccentric not findable isokinetic concentric. The results imply that the isokinetic concentric knee flexion strength test does not seem to reflect the whole picture of hamstring strength during the first year after anterior cruciate ligament reconstruction among patients with hamstring autograft