Regulation of Gait Cycle Phases during Noninvasive Electrical Stimulation of the Spinal Cord

A novel approach was designed to regulate the stepping movements in human by means of noninvasive electrical transcutaneous spinal cord stimulation (TSCS) to activate the flexor/extensor motor pools of the lower limbs in the gait cycle. Selective stimulation was delivered automatically based on signals from gyroscope sensors, which served to detect the stance and swing phases. The initiation of hip extension was a trigger for stimulating extensor pools (L1) during the stance phase, and the initiation of hip flexion was a trigger for stimulating flexor motor pools (T11) during the swing phase. In healthy subjects (n = 6) walking on a treadmill, stimulation at L1 with a frequency of 15 Hz decreased the duration of stance phase by 4% (p = 0.0457), increased the amplitude of movements in the hip joint by 11% (p = 0.0266), decreased the movement amplitude in the ankle joint by 17% (p = 0.0081), and increased EMG activities of the extensors vastus lateralis (VL) (by 31%, p = 0.0441) and gastrocnemius medialis (GM) (by 17%, p = 0.0465) and flexors biceps femoris (BF) (by 26%, p = 0.4637) and tibialis anterior (TA) (by 21%, p = 0.0215) relative to walking without stimulation. Stimulation at Т11 with a frequency of 30 Hz reduced the stance phase duration by 3% (p = 0.0318) and increased the amplitude of movements in the hip joint by 12% (p = 0.0467), the knee lifting by 25% (p = 0.0001), and the terminal anthropometric point height above the surface of support by 19% (p = 0.0001). The changes were accompanied by increases in muscle activities of the flexors BF (by 18%, p = 0.230) and TA (by 14%, p = 0.0170). The reciprocity coefficient decreased in thigh muscles by 15% (p = 0.0301) and increased in shin muscles by 5% (p = 0.0452). Alternating spatiotemporal stimulation at L1 and T11 did not significantly change the durations of the gait cycle and its phases, but changed the kinematic characteristics of movements. The amplitude of movements in the hip joint increased in the stance phase. In the swing phase, higher values were observed for the amplitude of movements in the hip joint, the knee lifting, and the terminal anthropometric point height above the surface of support. EMG activities of thigh and shin muscles increased during stimulation at L1 + T11. EMG activity of extensors was higher than that of flexors in the stance phase, while flexor EMG activity exceeded extensor activity in the swing phase. Thus, the data obtained show the possibility of TSCS selectively to activate the motor pools of the lower extremities, and control their activity to regulate the phases of the stepping cycle during human locomotion.