Real-time changes in rate of torque development and corticospinal excitability during transcutaneous spinal cord stimulation in healthy individuals

Transcutaneous spinal cord stimulation (tSCS) is used to induce neural plasticity and enhance motor function recovery following a stroke. Examining real-time changes under tSCS regulation would provide comprehensive insights into the mechanisms underlying motor functional recovery and neural plasticity. However, the real-time changes in the rate of torque development and neural excitability during tSCS remain unclear. This study explored the real-time changes in the rate of torque development and corticospinal excitability during tSCS. Twenty healthy individuals participated in two separate experiments, each with a tSCS condition and control condition. Under the tSCS condition, tSCS was applied to the Th11-Th12 spinous processes at an intensity twice the sensory threshold of the trunk muscles. The peak rate of torque development in the explosive lower limb extension movement in Experiment 1 and motor-evoked potential (MEP) amplitudes in Experiment 2 were assessed before the intervention and with (tSCS condition) or without tSCS (control).The peak rate of torque development and MEP amplitudes increased during tSCS compared to before tSCS (P = 0.038 and 0.047, respectively). However, the control condition had no significant effect. These findings demonstrate that tSCS enhances the rate of torque development and increases corticospinal excitability in healthy individuals, offering valuable fundamental insights into tSCS mechanisms and potential neurorehabilitation applications.