Purpose: Return to recreational activity is a common goal for the clinician and patient after ACL reconstruction (ACLR) and structured rehabilitation. Decreased peak knee flexion angle and external knee flexion moment during walking and jogging have been indicated as significant contributors to cartilage degeneration over time after knee joint injury. The purpose of this investigation was to measure the effects of 30 min of exercise on knee joint kinetics and kinematics in participants with a history of ACLR.
Methods: ACLR participants (n = 20, 9 females and 11 males) and healthy controls (n = 23, 11 females and 12 males) participated in an observational laboratory study. Gait analysis was performed on all subjects before and after a 30-min exercise protocol. Sagittal and frontal plane kinematics and kinetics were measured in the involved limb in the ACLR group and compared with healthy control participants across the gait cycle using 90% confidence intervals. Significant differences between groups were established as a consecutive 3% of the gait cycle in which 90% confidence interval did not overlap.
Results: Preexercise, ACLR participants were more hip flexed with higher magnitude external hip flexion moments and lower magnitude external knee flexion moments during the stance phase compared with healthy controls. ACLR participants experienced preexercise to postexercise declines in hip flexion angle and external hip flexion moment along with increases in external knee flexion moment when compared with healthy controls.
Conclusions: Exercise-related adaptations in hip and knee biomechanics are different in individuals with a history ACLR when compared with healthy controls despite a return to recreational activity. The biomechanical response to fatiguing exercise observed in this investigation may provide insight into one potential source of elevated knee injury risk and reduced long-term knee joint health after ACLR.