Abstract
OBJECTIVE: Based on cross-education theory, this study aimed to investigate whether Healthy-Side Lower-Limb Strength Training could promote neuromuscular function recovery of the injured limb in patients following anterior cruciate ligament reconstruction (ACLR) through central nervous system-mediated contralateral adaptive mechanisms. METHODS: A single-masked, randomized controlled trial was conducted with 40 patients at 5-6 weeks post-ACLR, who were randomly allocated to intervention and control groups (n = 20). The control group received conventional rehabilitation, while the intervention group received conventional rehabilitation plus Healthy-Side Lower-Limb Strength Training for 6 weeks. The Lysholm knee function score was used to assess knee joint function at baseline and post-intervention. A wireless surface electromyography system was used to measure root mean square (RMS) values of bilateral rectus femoris, semitendinosus, tibialis anterior, and lateral gastrocnemius muscles during maximal voluntary contraction and level walking. The activation ratios of the flexor and extensor muscle groups were calculated to evaluate muscle synergy patterns. The effects of Healthy-side strength training on bilateral lower limb muscle activation patterns and knee joint function were assessed through within-group pre- and post-intervention comparisons and between-group analyses. RESULTS: Following the 6-week intervention, Lysholm knee function scores improved significantly in both groups, with the intervention group demonstrating a significantly greater magnitude of improvement than the control group (P < 0.01). At baseline, the RMS values of all recorded muscles on the affected side were significantly lower than those on the unaffected side during both MVC and level walking in both groups (P < 0.01). Following the intervention, the intervention group demonstrated significant reductions in affected-to-unaffected limb asymmetry across all four muscle groups during both MVC and level walking (P < 0.01), whereas the control group exhibited significant asymmetry reductions in only a limited number of muscle groups during MVC alone (P < 0.01). In the intervention group, the RMS values of the bilateral rectus femoris, semitendinosus, tibialis anterior, and lateral gastrocnemius increased significantly during both MVC and level walking relative to baseline (P < 0.05). In contrast, the control group demonstrated significant improvements in only a limited subset of muscle groups. Between-group post-intervention comparisons revealed that the intervention group achieved significantly higher activation levels in the unaffected-side rectus femoris, bilateral semitendinosus, and unaffected-side tibialis anterior than the control group (P < 0.05). Both groups exhibited a declining trend in flexor-extensor co-contraction ratios; however, neither between-group nor within-group differences reached statistical significance (P > 0.05). CONCLUSION: Healthy-Side Lower-Limb Strength Training effectively promoted knee joint function recovery and enhanced bilateral lower limb muscle activation in patients following ACLR through cross-education mechanisms. These findings validate the clinical utility of cross-education theory and support Healthy-side strength training as an innovative rehabilitation strategy for early post-ACLR recovery. TRIAL REGISTRATION: Chinese Clinical Trial Registry ChiCTR2400087325. Registered on 25/07/2024.