Background:​ Anterior cruciate ligament (ACL) injuries are traumatic for young athletes and typically lead to surgical reconstruction (ACLR) followed by extensive rehabilitation. Athletes commonly demonstrate altered biomechanics during running post-ACLR. Persistent abnormalities in mechanics have been implicated as a mechanism of post-ACLR osteoarthritis. The purpose of this thesis was to investigate the longitudinal recovery of running biomechanics and the relationship to quadriceps performance and bone health.

Methods:​ Healthy baseline and post-ACLR data from the Badger Athletic Performance database (2011 to 2022) were utilized. Chapter 1 leveraged preinjury running data to describe changes in running mechanics over the first 12 months post-ACLR. Chapter 2 characterized the effect of running speed on knee biomechanics between 4-7 and 8-12 months post-ACLR. Chapter 3 assessed the relationship between recovery in running biomechanics and quadriceps performance 3-24 months post-ACLR. Chapter 4 explored the influence knee biomechanics during running and quadriceps performance have on bone mineral density between 3-24 months post-ACLR.

Results:​ Athletes demonstrated persistent deficits in surgical knee biomechanics during running post-ACLR compared to preinjury. Running speed and quadriceps performance were associated with changes in knee biomechanics, but neither fully resolved running asymmetries. Greater recovery of quadriceps rate of torque development post-ACLR was associated with less bone loss.

Conclusion:​ This thesis highlights persistent abnormalities in knee biomechanics during running following ACLR, identifies quadriceps performance and running speed as potential modifiable factors associated with running mechanics, and suggests that restoring quadriceps rate of torque development early and completely may help to minimize bone loss post-ACLR.