Anterior cruciate ligament (ACL) injuries are common orthopaedic injuries among athletes who participate in sports that involve cutting and changing directions. Many of these adolescent athletes intend to return to sports (RTS), and therefore undergo ACL reconstruction (ACLR). These athletes exhibit unfavorable landing biomechanics from muscle atrophy and asymmetrical neuromuscular control post-ACLR, putting them at a higher risk of re-injury. Thus, rehabilitation following ACLR is important to improve kinetic and kinematic outcomes and reduce re-injury risk. Biofeedback during rehabilitation is thought to be one way to potentially restore neuromuscular control deficits of athletes recovering from ACLR. Therefore, understanding the effectiveness of a biofeedback intervention on factors associated with re-injury among post-ACLR patients is essential in successful RTS. The purpose of this study is to analyze the effect of a 6-week biofeedback intervention on eccentric knee joint power (ECCKP), limb stiffness, and limb stiffness symmetry (using normalized symmetry index, NSI), in addition to secondary lower extremity outcomes that are associated with these metrics, during landing among patients following ACLR. This study used data collected from an ACL-Biofeedback Trial (ClinicalTrials.gov: AR069865) where participants were randomized into a biofeedback (BF) or control group (C). The BF group received visual and tactile feedback during a series of controlled squats while the C group participated in several online and in-person educational sessions. Participants completed 10 stop-jump tasks before (pre), after (post), and 6 weeks after (ret) the intervention. Kinetic, kinematic, and ground reaction forces (GRF) were collected from embedded force plates and 3D motion capture. Partaking in a biofeedback intervention did not improve ECCKP, limb stiffness, or limb stiffness NSI compared to controls. A group-by-time interaction was found for hip excursion (p=0.035), and a main effect of time was found for ECCKP, with this variable increasing by 18.5% from pre to ret (p=0.001). In addition, when considering surgical versus non-surgical limbs, this cohort exhibited interlimb asymmetries in stiffness, peak resultant GRF (rGRF), and time to reach peak rGRF (p<0.009). Further, a group-by-limb interaction (p=0.005) and a 7.1% reduction in peak rGRF were found from post to ret (p=0.02). Participants in this study also exhibited limb stiffness asymmetry greater than 10%, which supports existing literature that observed interlimb asymmetries in athletes following ACLR around the typical RTS time (9-12 months post-ACLR). The results from this analysis demonstrated that the current biofeedback intervention was inadequate in improving ECCKP, limb stiffness, and limb stiffness NSI, but additional biofeedback studies with larger sample sizes that investigate task dependencies are needed to better understand the effectiveness of biofeedback interventions. / Master of Science / Anterior cruciate ligament (ACL) injuries are common orthopaedic injuries among athletes who participate in sports that involve cutting and changing directions. Many of these adolescent athletes intend to return to their pre-injury level, therefore undergo a surgical procedure called ACL reconstruction (ACLR). However, following this procedure, athletes display unsafe and stiff landing patterns due to muscle weakness and asymmetrical neuromuscular, or mind-body, control post-ACLR, which increases their risk of re-injury once they return to sport (RTS) following recovery. Rehabilitation for patients following ACLR is of the utmost importance in improving unsafe movement patterns to reduce the risk of re-injury. Biofeedback training refers to receiving external signals that can be processed and transferred to the muscles in the body. This technique aims to restore the neuromuscular deficits of athletes following ACLR and could potentially be helpful during ACLR rehabilitation. Therefore, understanding the effectiveness of a biofeedback intervention on outcomes associated with an increased risk of re-injury in patients following ACLR is important to safely RTS. The purpose of this study is to determine the effect of a 6-week biofeedback intervention on the ability of the knee to absorb impact forces (quantified as eccentric knee joint power, ECCKP), limb stiffness, and limb stiffness symmetry (measured with normalized symmetry index, NSI), along with secondary outcomes related to these variables, among patients following ACLR. This study used data collected from an ACL-Biofeedback Trial (ClinicalTrials.gov: AR069865) where participants were randomized into a biofeedback (BF) or control group (C). The BF group received visual and resisted feedback during a series of controlled squats while the C group participated in several online and in-person educational sessions. Participants completed 10 stop-jump tasks before and after the intervention, and biomechanical data was obtained. The biofeedback intervention did not result in an improved ability for the knee to absorb impact from landing, and it was not able to decrease limb stiffness or limb stiffness asymmetry. It was able to improve hip excursion, which allows for a favorable, less upright posture when landing. ECCKP improved for both groups, indicating that the biofeedback did not add extra benefit to the participant's rehabilitation outside of the study. Asymmetries were observed between the surgical and non-surgical limbs in limb stiffness, peak GRF, and the time it takes to reach this peak GRF. This sample exhibited limb stiffness asymmetry greater than the recommended 10% threshold, raising concern for when these athletes RTS. The results from this analysis demonstrated that the current biofeedback intervention was inadequate in improving ECCKP, limb stiffness, and limb stiffness NSI, but biofeedback in ACLR rehabilitation can still be efficacious in improving hip biomechanics and overall neuromuscular control but may be task-dependent and call for a larger sample size.