Most lower-extremity assistive robots are designed to actively assist gait1–7 without considering long-term neuromuscular adaptations8–11. Here we present a lightweight (0.96 kg) robot that administers isokinetic resistance training to sustain neuromuscular rehabilitation after removal. The device integrates a variable stiffness mechanism with a back-drivable damping motor to make available safe, portable and customizable resistance training to juveniles with spinal muscular atrophy (SMA) type II. In a study involving six such juvenile participants, substantial improvements in lower-extremity motor ability were observed after 6 weeks of robot-assisted training in a clinical trial (NCT06648486). Participants gained the ability to perform sit-to-stand transitions with hands on knees but without external support from an average seated knee flexion angle of 111° to 104°, representing a 7° improvement from pre-intervention. This improvement was accompanied by greatly increased bilateral knee joint function (peak torque: +130%; range of motion (ROM): +51%; work: +97%). Marked physiological quadriceps muscle hypertrophy was observed (anatomical cross-sectional area (ACSA): +12%; volume: +19%; physiological cross-sectional area (PCSA): +21%) alongside enhanced femoral nerve conduction (compound muscle action potential (CMAP): +19%), representing physiological changes consistent with the observed functional improvements. Notably, participants were able to retain their gains after discontinuing isokinetic training and returning to their conventional physiotherapy routines. These results indicate that even temporary exposure to isokinetic resistance training through wearable robotics may facilitate enduring neuromuscular recovery.
