Lower limb motor activity generated by transcutaneous lumbar SCS. (A) Stimulation method of transcutaneous SCS. Drawings of the stimulating paravertebral and abdominal reference electrodes with respect to the spine and spinal cord. (B) EMG activities generated in paralyzed lower limb muscles by partial (50%) body-weight supported and manually assisted treadmill stepping without (left) and with sub-motor transcutaneous SCS. EMG recordings were derived from the right quadriceps (Q), hamstrings (Ham), tibialis anterior (TA), and triceps surae (TS) along with goniometric data from the knee (Knee angle). Black bars mark stance phases; treadmill speed was 0.33 m/s. Continuous transcutaneous SCS at 30 Hz and 25 V produced rhythmic gait-synchronized EMG activities. Lower limb motor threshold was 28 V in a supported standing position. Subject with chronic, motor-complete (AIS A), mid-thoracic (motor level: T6) traumatic SCI. (C) EMG activities generated in paralyzed lower limbs by partial (50%) body-weight supported and manually assisted treadmill stepping without (left) and with above-motor threshold transcutaneous SCS; treadmill belt speed was 0.39 m/s. Transcutaneous SCS at 30 Hz and 35 V produced burst-like activities in all right lower limb muscles, with in-phase oscillation that were not synchronized to the manually controlled step-cycle. Lower limb motor threshold was 25 V in a passive supported standing position. Subject with chronic, motor-complete (AIS B), low-cervical (motor level: C6) traumatic SCI.