Extended Data Fig. 4: Single-joint movements enabled by targeted EES.

Step 1: participants are placed in standardized positions to allow assessment of voluntary torque production at a single joint (isometric contractions) without and with targeted EES. Step 2: EES protocols elaborated from single-pulse experiments (Extended Data Figs. 2, 3) are optimized for each task using multipolar configurations and adjustments of EES amplitude and frequency. Step 3: sequence of each trial. Participants were asked to produce a maximal voluntary contribution, but failed in most cases, as evidenced by the absence of EMG activity during this period. While they continued trying to activate the targeted muscle, EES was switched on. After a few seconds, participants were instructed to stop their voluntary contribution. After a short delay, EES was switched off. For each sequence, the produced torque and EMG activity of the key agonist and antagonist muscles acting at the targeted joint were calculated over the four indicated phases of the trial. Plots report the measured torques and EMG activity during the various phase of the trial for the left legs of all participants for the four tested joints (cyan, flexor; magenta, extensor), together with EES parameters and electrode configurations. All measurements were performed before rehabilitation, except for hip extension in P1 and P2 (not tested before), and ankle extension in P3 (no capacity before rehabilitation), which were carried out after rehabilitation. Targeted EES enabled or augmented the specific recruitment of the targeted muscle, which resulted in the production of the desired torque at the targeted joint, except for ankle extension of P2. Plots show quantification of the EMG activity and torque for n = 3 trials per condition. Note that hip flexion can be enabled or augmented with EES targeting L1 and/or L4 posterior roots (heteronymous facilitation of flexor motor neuron pools).