Objective <p>Grounded in cross-education theory, this study evaluated the effects of contralateral knee functional training on knee function, pain, kinesiophobia, plantar load distribution, and stance-phase parameters in patients during the early postoperative period after anterior cruciate ligament reconstruction (ACLR), to inform the optimisation of early rehabilitation protocols.</p> Methods <p>In this single-blind, randomised controlled trial, 40 patients at 5–6 weeks post-ACLR were enrolled and randomly allocated 1:1 to an intervention group (<i>n</i> = 20) or a control group (<i>n</i> = 20). The intervention group received a 6-week programme of contralateral knee functional training in addition to routine rehabilitation, whereas the control group received routine rehabilitation alone. Both groups completed sessions three times per week. Knee function, pain, and kinesiophobia were assessed using the Lysholm Knee Scoring Scale, Visual Analogue Scale (VAS), and Tampa Scale for Kinesiophobia (TSK-17), respectively, before and after the intervention. In addition, single-limb stance-phase duration and peak pressures at the forefoot, midfoot, and hindfoot were recorded using a Zebris FDM-2 plantar pressure platform.</p> Results <p>Baseline characteristics were comparable between the two groups (all <i>P</i> &gt; 0.05). No patients were lost to follow-up, and the training completion rate reached 100% in both groups. With respect to knee joint function, the mean Lysholm score change in the experimental group was 12.45 points, exceeding the minimal clinically important difference (MCID = 8.9 points), whereas the corresponding change of 5.80 points in the control group did not reach this threshold. The between-group difference following the intervention was statistically significant (<i>P</i> &lt; 0.001, d = 2.071), as was the group × time interaction effect (<i>P</i> &lt; 0.001, η² = 0.443). With respect to kinesiophobia, the reduction in TSK-17 scores exceeded the MCID (5.6 points) in both groups, and the reduction was significantly greater in the experimental group than in the control group (<i>P</i> &lt; 0.001, d = 2.348); the group × time interaction effect was also statistically significant (<i>P</i> &lt; 0.001, η² = 0.271). With respect to pain, VAS scores decreased significantly from baseline in both groups, and the magnitude of change exceeded the MCID (15&#xa0;mm) in each group; however, the between-group difference in change scores was not statistically significant (<i>P</i> = 0.069). With respect to plantar loading characteristics and stance-phase parameters, all indicators improved significantly from baseline in both groups. The main effect of group on peak forefoot pressure was statistically significant, indicating an overall between-group difference in forefoot loading levels, whereas neither the main effect of group nor the group × time interaction effect reached significance for the remaining indicators.</p> Conclusion <p>Supplementing conventional rehabilitation with functional training of the uninvolved (contralateral) knee improved knee joint function and effectively alleviated kinesiophobia during the early postoperative period after ACLR. Between-group differences in the indicators of pain and plantar loading were not statistically significant, suggesting that the observed improvements were more likely attributable to natural postoperative recovery than to a specific effect of the intervention. This protocol is safe and feasible, imposes no additional loading on the affected limb, and may serve as a beneficial adjunct to conventional early postoperative rehabilitation after ACLR.</p> Trial registration <p>Chinese Clinical Trial Registry, ChiCTR2400087325. Registered on 25/07/2024.</p>