Torque–Velocity is Associated With Voluntary Activation and Corticospinal Excitability in Healthy Knees, but Not Following Anterior Cruciate Ligament Reconstruction

CONTEXT: Following ACL reconstruction (ACLR) arthrogenic muscle inhibition limits quadriceps function. Arthrogenic muscle inhibition is characterized via a decreased central activation ratio and a higher active motor threshold. Although previous research has identified reductions in the torque-velocity relationship post-ACLR, our aim was to determine if this relationship is associated with measures of arthrogenic muscle inhibition following ACLR. DESIGN: Cross-sectional. METHODS: Nine participants (5 females and 4 males; 175.8 [7.8] cm, 79.4 [14.2] kg, 20.6 [28.8] mo postsurgery) following ACLR and 24 control participants (20 females and 4 males; 167.6 [8.1] cm, 66.9 [13.3] kg) completed isokinetic knee extension at 60, 90, 180, and 270°/s. A superimposed burst was delivered during maximal volitional isometric contraction using a square-wave stimulator to obtain central activation ratio. Transcranial magnetic stimulation was applied to obtain active motor threshold in ACLR involved limbs and control limbs. Correlations between 2-point torque-velocity relationships, central activation ratio, and active motor thresholds were analyzed separately by group with a false discovery rate correction applied. RESULTS: The ACLR central activation ratio was not correlated with the torque-velocity relationship, but the control central activation ratio positively correlated with multiple 2-point torque-velocity relationships (q < 0.05). The active motor threshold was higher in the ACLR participants (ACLR: 34.8 [7.8], control: 27.5 [9.4]). In the ACLR, the limbs active motor threshold was not correlated with torque-velocity relationships, but the control limb active motor threshold was correlated with T:V60-0 (r = .52, P < .001, q = 0.02); T:V90-0 (r = .47, P < .002, q = 0.024); T:V180-0 (r = .34, P = .04, q = 0.048); T:V270-0 (r = .37, P = .03, q = 0.045); and T:V180-60 (r = .41, P = .013, q = 0.037). CONCLUSION: Two-point torque-velocity relationships incorporating isometric contractions were associated with both voluntary activation and corticospinal excitability in healthy participants but not in ACLR limbs.