Abstract
OBJECTIVE: Individuals with a history of anterior cruciate ligament reconstruction (ACLR) often experience altered biomechanics, such as dynamic knee valgus (DKV), which increases the risk of re-injury. Functional fatigue, resulting from prolonged physical exertion, can further compromise neuromuscular control, balance, and proprioception, exacerbating biomechanical risk factors. This study investigates the impact of functional fatigue on kinematics, balance, and proprioception in individuals with ACLR and DKV. METHODS: This experimental study used a mixed-model design with a between-group factor (fatigue vs. no-fatigue) and a within-subject factor (pre- vs. post-fatigue). Forty-four male participants with ACLR and DKV underwent a Shortened Cycle Fatigue Protocol. Assessments included lower-limb kinematics (LESS), dynamic balance (Y-Balance Test), and knee proprioception (joint repositioning error at 30° and 60°). RESULTS: Functional fatigue led to significant worsening in lower-limb kinematics, dynamic balance, and knee proprioception in the experimental group. Specifically, post-fatigue assessments showed higher LESS scores (p < 0.001), decreased Y-Balance performance (p < 0.001), and increased joint repositioning error at 30° (p < 0.001) and 60° (p < 0.001) compared to their baseline. In contrast, the control group maintained stable performance across all measures, highlighting the impact of functional fatigue on biomechanical risk factors. CONCLUSION: Functional fatigue significantly impairs proprioception, alters lower extremity kinematics, and decreases dynamic balance in individuals with ACLR and DKV. These findings underscore the importance of incorporating fatigue management strategies into rehabilitation and training protocols to mitigate the risk of re-injury. Clinicians should consider incorporating proprioception training, dynamic balance exercises, and muscular endurance conditioning to mitigate fatigue-induced biomechanical impairments and promote safe return-to-sport practices.