FIG. 4.

Self-initiated body-weight displacements. (A) Modulation of EMG activity in the left leg muscles and the COP signal during self-initiated body-weight displacements in the mediolateral or anteroposterior directions before (blue traces) and after (red traces) stand training in a representative participant (P2) without and in the presence of tSCS delivered over the L1 with frequency of 15 Hz. The directions of the body-weight displacements are indicated on the top. Lower panel presents individual spinally evoked motor potentials in the initial (center) position and during the body-weight displacements in a particular direction. Note VL activity (arrows) occurred independently of the stimulation during the body-weight displacements following stand training. (B) Pooled data (n = 6) demonstrating modulatory effects of the body-weight displacements in the mediolateral or anteroposterior directions on the magnitude of spinally evoked motor potentials in the left and right leg muscles during standing enabled by tSCS following training. The magnitude of spinally evoked motor potentials was normalized to the peak-to-peak amplitude of each muscle at the initial position, that is prior to movement in either direction (shown by red dashed line). COP, center of pressure; EMG, electromyogram; tSCS, transcutaneous electrical spinal cord stimulation; VL, vastus lateralis.