Biofeedback Impact on Limb Stiffness and Joint Power in Patients With ACL Reconstruction—A Secondary Analysis

The purpose of the study was to examine the effects of a biofeedback intervention on limb stiffness and eccentric knee joint power (ECCKP) symmetry, as well as related landing biomechanics, in individuals post-anterior cruciate ligament reconstruction (ACLR). Thirty-three participants (Biofeedback: n = 14; Control: n = 19) completed a 12-week protocol with assessments at baseline, post-intervention, and retention time-points. Linear mixed-effects models evaluated the effects of group and time-point on ECCKP normalized symmetry index (NSI) and limb stiffness NSI. Linear mixed-effects models evaluated the effects of group, time-point, and limb (surgical vs. non-surgical) on limb stiffness, peak relative ground reaction force (rGRF), change in limb length, and time to peak rGRF during landing. There were no significant group × time-point interactions found for ECCKP NSI or limb stiffness NSI (p > 0.05). For limb stiffness, the non-surgical limb showed greater stiffness (p = 0.001). Peak rGRF was higher in the non-surgical limb (p = 0.001) and at baseline compared to post-intervention (p = 0.023). Time to peak rGRF was longer in the non-surgical limb (p = 0.008). No significant effects were found for change in limb length. Overall, the biofeedback intervention did not significantly improve ECCKP or limb stiffness symmetry post-ACLR. Persistent symmetry deficits in landing biomechanics were evident, particularly between surgical and non-surgical limbs. Given that the study was likely underpowered to detect moderate effects, findings should be interpreted with caution. Larger, adequately powered studies are warranted to further evaluate the effect of biofeedback in improving symmetry during dynamic tasks after ACLR. Trial Registration: ClinicalTrials.gov: AR069865.