Hamstrings corticomotor and neuromechanical function in individuals with anterior cruciate ligament reconstruction

Hamstrings neuromuscular alterations are common after anterior cruciate ligament (ACL) reconstruction; however, their neural origins remain unclear. While quadriceps corticospinal function after ACL reconstruction (ACLR) is well studied, similar data for hamstrings are lacking. We aimed to assess hamstrings corticomotor and neuromechanical function and their associations in individuals with ACLR. Twenty-three adults with primary, unilateral ACLR via hamstrings tendon autograft were assessed (time from surgery = 46.9 ± 26.3). Corticomotor function was quantified via active motor threshold (AMT), motor evoked potential (MEP), short-interval intracortical inhibition, intracortical facilitation (ICF), and cortical silent period (CSP) in semitendinosus. Neuromechanical function was quantified via maximal voluntary isometric contraction (MVIC) torque, early and late-phase rate of torque development (RTD₁₀₀, RTD₂₀₀), and semitendinosus electromyographic amplitude.Paired-samples t-tests or Wilcoxon signed-rank tests compared outcomes between limbs. Associations between involved limb outcomes were analyzed using correlation coefficients. Involved limbs exhibited shorter CSP (p = 0.005), lower MVIC torque (p = 0.002), and lower RTD₂₀₀ (p = 0.002) than uninvolved limbs. Lower AMT (r = 0.462, p = 0.026) and ICF (r = 0.510, p = 0.013) associated with lower RTD₂₀₀, and lower MEP associated with lower MVIC torque (r = 0.448, p = 0.032). Hamstrings neural adaptation following ACLR, characterized by lower corticospinal inhibition (semitendinosus) and torque deficits, highlights the need for rehabilitation approaches targeting both neural and peripheral impairments.