Extended Data Fig. 6: Configuration of activity-specific stimulation protocols.

Step 1, The participant is lying supine in a relaxed posture. Wireless sensors are positioned over selected leg muscles to monitor electromyographic signals in conjunction with leg kinematics using an optical 3D motion capture system. Step 2, Intraoperative imaging of the final paddle lead position guides the realignment of the paddle lead with respect to the personalized model of the interactions between EES and the spinal cord. The optimal cathode to target specific motor neurons are inferred based on the location of the electrodes with respect to the dorsal roots and location of motor neurons identified from fMRI measurements. Step 3, The performance of the preselected optimal cathode is assessed using trains of pulses delivered with predefined frequency ranges that are optimal for the targeted motor neurons. Step 4, The muscle responses are quantified from 40 to 500 ms after stimulation onset, and then normalized with respect to a baseline window selected 500 ms before stimulation onset. The relative amplitudes of muscle responses are represented in a polar plot that allows to appreciate the relative recruitment of each muscle. Step 5, A physiotherapist grades the precision of the elicited movements and muscle activity based on a simple clinical scale that enables the quick adjustment of anode and cathode configurations to achieve the most optimal selectivity. Step 6, This procedure enables the rapid elaboration of a library of anode and cathodes targeting specific muscles and motor hotspots, which are then implemented in preprogrammed stimulation templates that aim to reproduce the natural activation of muscles during the desired activity.