BACKGROUND: Anterior cruciate ligament reconstruction (ACL-R) significantly affects lower limb biomechanics, particularly during dynamic movements like jumping. The countermovement jump (CMJ) is a commonly used test to evaluate force production and asymmetry in post-ACL-R individuals. This study aimed to compare eccentric and concentric forces during the CMJ between ACL-R patients and healthy controls. METHODS: This retrospective study included 56 ACL-R patients and 47 recreational athletes. All participants performed CMJs on a dual force plate to measure eccentric mean force (ECC), Concentric mean force (CON), and limb symmetry index (LSI). A mixed ANOVA was performed to compare ECC LSI and CON LSI between the ACL-R and control groups. RESULTS: CMJ height was significantly lower in the ACL-R group compared to the control group (-25.4%, p < 0.001), with a lower ECC LSI (-7.7%, p < 0.001) and CON LSI (-10.0%, p < 0.001). CONCLUSION: Six months after ACL-R, both eccentric and concentric force production remain compromised, with significant inter-limb asymmetries. These findings highlight the need for targeted rehabilitation strategies to restore force symmetry and optimize return-to-sport readiness.