Number of conditioning trials, but not stimulus intensity, influences operant conditioning of brain responses after total knee arthroplasty

Purpose:<bold> </bold>The primary purpose of this randomized, cross-sectional study was to determine whether operant conditioning of motor evoked torque (MEPTORQUE) in individuals with total knee arthroplasty (TKA) increases quadriceps MEPTORQUE responses within a single session and induces acute corticospinal adaptations by producing sustained increases in MEPTORQUE after training. A secondary purpose was to determine if these changes were affected by the stimulus intensity and number of training trials. Methods:<bold> </bold>Thirty participants were block-randomized into one of three groups based on the participant's active motor threshold (100%, 120%, and 140%) to evaluate the effect of stimulus intensity. Participants received three blocks of conditioning trials (COND), where they trained to increase their MEPTORQUE. Control (CTRL) transcranial magnetic stimulation pulses were provided before and after each COND block to establish baseline corticospinal excitability and to evaluate the effect of the number of training trials. Two MEPTORQUE recruitment curves were collected to evaluate the effect of up-conditioning on acute corticospinal adaptations. Results:<bold> </bold>TKA participants were able to successfully increase their MEPTORQUE in a single session (F-3,F-81 = 10.719, p < 0.001) and induce acute corticospinal adaptations (F-1,F-27 = 20.029, p < 0.001), indicating sustained increases in quadriceps corticospinal excitability due to operant conditioning. While the stimulus intensity used during training did not affect the ability to increase MEPTORQUE (F-2,F-26 = 0.021, n.s.) or its associated acute adaptations (F-2,F-27 = 0.935, n.s.), the number of training trials significantly influenced these outcomes (F-3,F-81 = 10.719, p < 0.001; F-3,F-81 = 4.379, p = 0.007, respectively). Conclusion: Operant conditioning is a feasible approach for improving quadriceps corticospinal excitability following TKA. While any of the three stimulus intensities evaluated in this study may be used in future operant conditioning interventions, using a low or moderate stimulus intensity and 150 training trials are recommended to improve treatment efficiency and patient adherence.