Patients With ACL Reconstruction Via Semitendinosus Graft Do Not Perform Nordic Hamstring Exercise Effectively

Weakness and atrophy of the medial hamstrings are common after anterior cruciate ligament reconstruction with semitendinosus autograft (ACLR-ST). Nordic hamstring exercise (NHE) preferentially activates the medial hamstrings, but the ability of patients with ACLR to effectively perform NHE is unclear. PURPOSE: To investigate interlimb asymmetry in eccentric hamstrings torque during NHE contractions in individuals with ACLR-ST. METHODS: 15 patients with ACLR-ST (9 female, 29.3 ± 3.3 years, 47.1 ± 26.2 months from surgery) performed five NHE contractions on a dynamometer. Force tracings were averaged per participant to create ensemble curves, converted to body mass-normalized torque (Nm/kg), and averaged across all participants. Statistical parametric mapping was used to compare limbs over the entire NHE contraction (1-100%). Regions where interlimb differences exceeded a critical z-score (95% confidence) were deemed statistically asymmetric. Limb symmetry index (LSI) was used to quantify interlimb asymmetry. Paired t-tests were used to compare peak torque and time to peak torque between limbs. Effect sizes (d) were calculated for all comparisons. RESULTS: NHE peak torque did not differ between limbs (LSI = -13.2 ± 21.2%, d = -0.21, p = .056), but occurred later in the contraction for the involved limb (70.1 ± 9.7% vs. 66.8 ± 12.9%, d = 0.29, p = .024). Interlimb asymmetry occurred within 7-58% of the contraction (LSI = -27.9 ± 7.5%, d = -0.50, z > 2 [uncorrected]), but was largest from 23-49% (LSI = -29.5 ± 4.5%, d = -1.16, z > 3 [corrected]) (Figure 1). CONCLUSIONS: Despite no differences in peak torque, patients with ACLR-ST achieve peak torque later in the involved limb and exhibit moderate-to-large magnitude interlimb asymmetry during the early-to-mid phases of NHE. This suggests that peak torque alone does not fully capture muscular impairments and that patients with ACLR-ST perform NHE ineffectively, which holds implications for clinical implementation.