EMG responses to electrode array stimulation during stepping. Average (10 consecutive steps) rectified EMG (linear envelope) for an ankle flexor (TA) and two ankle extensor (Sol and MG) muscles during stimulation (at 40 Hz, pulse width 0.2 ms, and 3–4 V) using different electrode combinations. A and B: coordinated bilateral stepping with good body weight support. C and D: bilateral stepping with lower body weight support compared to A and B. A, B, C, and D: cases demonstrating good rhythmic bilateral stepping ability with varying degrees of body weight support depending on the position of the cathode and anode on the spinal cord. E: Uncoordinated and non-rhythmic stepping during stimulation with the cathode positioned more caudal than the anode demonstrating the importance of having the cathode at a more rostral segment compared to the anode. Note that the time scale for E is the longest due to extended periods of dragging. F: rhythmic stepping movements with very low (near zero) body weight support, demonstrating the need to position the cathode and anode at different columns to facilitate stepping with good body weight support. Note the EMG amplitude scale in A and B are an order of magnitude higher than in C-F.