BACKGROUND: After anterior cruciate ligament reconstruction (ACLR), chronic changes in knee joint biomechanics during higher level tasks, such as running, may negatively impact long-term knee joint health. Among the factors that contribute to these chronic changes, the influence of quadriceps strength on knee joint biomechanics during running is not well understood. HYPOTHESIS: Higher involved limb quadriceps strength (peak torque and rate of torque development [RTD]) and limb symmetry index (LSI) will be positively associated with greater peak knee flexion angle and peak knee extensor moment during running. STUDY DESIGN: Cross-sectional study. LEVEL OF EVIDENCE: Level 3. METHODS: Peak knee extensor moment and peak knee flexion angle were analyzed during the stance phase of running, 6 months following ACLR (n = 26
18 female participants
age, 19 ± 5.0 years). Involved limb quadriceps strength and LSI were calculated for peak torque and RTD. Linear regression models were used to analyze the relationship between involved limb and LSI values of quadriceps peak torque and RTD to peak knee flexion angle and peak knee extensor moment. RESULTS: Quadriceps peak torque ( CONCLUSIONS: Quadriceps peak torque and RTD are positively associated with running kinetics 6 months after ACLR. Peak torque and RTD LSI were not associated with running mechanics after ACLR. CLINICAL RELEVANCE: Quadriceps peak torque and rate of torque development are positively associated with running mechanics after ACLR. Clinicians should consider objective assessments of quadriceps strength before initiating running after ACLR.