Extended Data Fig. 9: Selective recruitment of trunk muscles.

Step 1, Trunk and abdominal muscles are primarily innervated by motor neurons located in the thoracic region of the spinal cord. The new paddle array enables targeting the dorsal roots projecting to the T12 spinal segment, allowing the recruitment of trunk and abdominal muscles. Step 2, Single pulses of EES at increasing amplitude are delivered over electrodes to evaluate their ability to recruit trunk and abdominal muscles. Muscle responses are calculated, normalized, and then represented in a polar plot. The selectivity of trunk/abdominal versus leg muscle activation is calculated with a selectivity index formula. Side-specific recruitment of trunk and abdominal muscles is obtained with the upper electrodes of the new paddle lead. Step 3, Polar plots reporting the activation of trunk/abdominal muscles versus leg muscles when delivering EES through various electrodes of the new paddle lead, as indicated by the number referring to the electrodes depicted in step 2. Step 4, Trains of EES are delivered through the same electrodes as in Step 2 to elicit kinematic responses. For each tested electrode, the panels depict the mean time-dependent trajectory of trunk and knee movements in the plane perpendicular to the direction of gravity, and bar plots reporting the mean amplitude of trunk and knee movement in abduction or adduction. Electrodes 1 and 4, which are located over the top row of the new paddle lead, elicited side-specific trunk movement without disturbing knee movements.