Neuroadaptation In ACLR Patients During Force Reproduction Task Compared To Health Controls

The heightened quadriceps activation observed in patients who have undergone anterior cruciate ligament reconstruction (ACLR) in response to unexpected Transcranial Magnetic Stimulation (TMS) compared to healthy individuals (CONT) suggests a potential neuroadaptation, particularly within the corticospinal pathway. However, the extent of neuroadaptation within other regions of the brain during knee strength tasks remains unclear. PURPOSE: To investigate brain activation patterns in response to TMS pulses during isometric knee extension between the ACLR and CONT. METHODS: Electrocortical activation of 6 ACLR (20.17 ± 1.60 yrs, 70.68 ± 12.04 kg, 169.65 ± 7.48 cm) and 5 CONT (21.00 ± 1.73 yrs, 65.77 ± 13.61 kg, 166.62 ± 11.99 cm) subjects were recorded using a 64 channel electroencephalograph (EEG) system during an isometric force reproduction task. Sixty TMS pulses (minimum of 120% active motor threshold) were randomly delivered to the primary motor cortex, while maintaining 10% of maximal voluntary isometric contraction (MVIC). Processed and cleaned EEG data were used to compute N100 (80 ~ 200 ms) and P200 (160 ~ 300 ms) event-related potentials (ERP, μV) at fronto-central (RO3), motor (RO1) and parietal (RO2) regions of interest. Motor evoked torque (MET, %), reflecting peak torque normalized to 100% TMS intensity, was computed. ERP and MET comparisons were made using independent t-tests. RESULTS: Our preliminary data showed a significant difference for ERP P200 at RO1 (t[1,9] = 1.847, p = 0.049) that revealed less peak power in the ACLR (5.30 ± 2.34 μV) than the CONT (12.80 ± 9.72 μV). However, MET (t[1,9] = 3.018, p = 0.003) showed that TMS increased involuntary quadriceps torque in ACLR (177.97 ± 85.92%) than CONT (87.88 ± 42.13%) subjects. CONCLUSION: The heightened torque post-TMS in ACLR, compared to CONT, may suggest altered corticospinal tract activation, while lower ERP amplitudes may point to potential adaptations in the motor cortex. Future research should explore the link between reduced cerebral cortex activity and increased corticospinal tract activation.