Introduction: Since people experience fatigue after anterior cruciate ligament injury during exercises, it is important to understand how fatigue affects the biomechanical movement patterns. Therefore, this study aimed to investigate the effect of fatigue on ground reaction force variables during single-leg landing in athletes with a history of an anterior cruciate ligament sprain. Methods: it was a case-control study conducted in the University Laboratory. The sample consisted of 36 male athletes who were divided into three groups: 12 people with Anterior Cruciate Ligament Reconstruction (ACLR), 12 people with Anterior Cruciate Ligament Deficiency (ACLD), and 12 people as the control group. Fatigue was induced via the repetitive sets of double-leg squats (n=8), which were interspersed with the sets of countermovement jumps (n=2) and single-leg landings (n=3) until squats were no longer possible. A 2×2 repeated-measures multivariate analysis of variance was used to detect the main effects of group (ACLD, ACLR, control) and fatigue state (prefatigue, postfatigue) on the ground reaction forces variables. Results: The results showed a significant decrease in the peak vertical force and internal-external ground reaction force in the ACLD group after fatigue. Regardless of the fatigue state, the peak vertical ground reaction force in ACLD and ACLR groups was significantly lower than that in the control group. Conclusion: The athletes with the ACL injury, regardless of the selective treatment type, use compensatory strategies to reduce the contact forces on the lower extremity, compared with healthy athletes.
