Background The purpose of this study was to analyze sagittal-plane knee biomechanics in individuals with ACL reconstructions in bilateral countermovement jumps. This aimed to determine potential knee compensation strategies during a high-demanding symmetrical movement task from pre to six months post-ACL reconstruction. Methods 20 ACL-reconstructed individuals were tested pre-operatively, and then seven weeks, three months, and six months after reconstruction. Additionally, a matched control group was analyzed. Data were sampled with 3D motion capture and two force plates. The following kinematic data were analyzed: peak knee flexion during countermovement, knee angle at toe-off, and knee flexion excursion during landing. The following kinetic data were analyzed: peak knee extension moments during countermovement and landing. Findings ACL-reconstructed individuals showed significant increases in knee flexion during countermovement and knee flexion excursion during landing from six weeks to six months after reconstruction but they remained significantly below the level of the controls. The reconstructed knee joint showed increased flexion at toe-off compared to the non-injured leg at all test sessions. ... mehrKnee extension moments during countermovement increased up to six months after reconstruction, but remained deficient in ACL-reconstructed individuals during countermovement and landing compared to the controls. Interpretation Although ACL-reconstructed individuals showed increases in most kinematic and kinetic variables, they remained below the controls at six months post-ACL reconstruction. The deficits between contralateral legs and compared to the controls show that six months post-ACL reconstruction, knee joint functionality was still not equal between reconstructed and non-injured legs or in comparison to controls.