The Influence of Quadriceps Strength and Rate of Torque Development on the Recovery of Knee Biomechanics During Running After Anterior Cruciate Ligament Reconstruction

Background: After anterior cruciate ligament reconstruction (ACLR), altered surgical knee biomechanics during running is common. Although greater quadriceps strength is associated with more symmetrical running knee kinetics after ACLR, abnormal running mechanics persist even after resolution of quadriceps strength deficits. As running is a submaximal effort task characterized by limited time to develop knee extensor torque, quadriceps rate of torque development (RTD) may be more closely associated with recovery of running knee mechanics than peak torque (PT). Purpose: To assess the influence of recovery in quadriceps PT and RTD symmetry on knee kinematic and kinetic symmetry during running over the initial 2 years after ACLR. Study Design: Cohort study; Level of evidence, 3. Methods: A total of 39 Division I collegiate athletes (106 testing sessions; 19 female) completed serial isometric performance testing and running analyses between 3 and 24 months after ACLR. Athletes performed maximal and rapid isometric knee extension efforts with each limb to assess PT and RTD between-limb symmetry indices (PT LSI and RTD LSI ), respectively. Peak knee flexion difference (PKF DIFF ) and peak knee extensor moment limb symmetry index (PKEM LSI ) during running were computed. Multivariable linear mixed-effects models assessed the influence of PT LSI and RTD LSI on PKF DIFF and PKEM LSI over the initial 2 years after ACLR. Results: Significant main effects of RTD LSI ( P < .001) and time ( P≤ .02) but not PT LSI ( P≥ .24) were observed for both PKF DIFF and PKEM LSI models. For a 10% increase in RTD LSI , while controlling for PT LSI and time, a 0.9° (95% CI, 0.5°-1.3°) reduction in PKF DIFF and a 3.5% (95% CI, 1.9%-5.1%) increase in PKEM LSI are expected. For every month after ACLR, a 0.2° (95% CI, 0.1°-0.4°) reduction in PKF DIFF and a 1.3% (95% CI, 0.6%-2.0%) increase in PKEM LSI are expected, controlling for PT LSI and RTD LSI . Conclusion: Quadriceps RTD LSI was more strongly associated with symmetrical knee biomechanics during running compared with PT LSI or time throughout the first 2 years after ACLR.