After spinal cord injury, the ability to step is better at faster walking speeds

Human spinal cord interprets velocity dependent afferent information during stepping

We compared the EMG activity from SCI subjects over a range of treadmill speeds during stepping using BWST and manual assistance that facilitated the kinetics and kinematics of walking. We assessed whether the human spinal cord can respond to the mechanical demands imposed on the motor system by changing the treadmill speed. We assessed step cycle mechanics as well as lower limb muscle EMG burst duration and mean amplitudes of clinically complete SCI subjects. Step cycle duration decreased as treadmill speed increased, resulting primarily from a decrease in stance duration with a minimal decrease in swing duration. EMG amplitudes were higher and burst durations were shorter at faster treadmill speeds. These results are similar to adaptations observed in non-disabled humans during walking, intact animals during stepping, and spinalized animals during fictive locomotion. These results indicate that the human spinal cord adapts to changes in speed by interpreting velocity dependent afferent information to generate effective efferent activity during stepping.

Fig. 1

Fig. 1 Data from one limb of clinically complete SCI subjects during stepping. Treadmill speeds ranged from 0.27 m/s to 1.52 m/s. Step cycle (square), stance (triangle), and swing (circle) durations(s) versus treadmill speed (m/s).

Fig. 2

Fig. 3

Fig. 3 EMG burst duration(s) from SOL (circle), MG (square), and VL (triangle) versus step cycle duration(s). Each point represents the average (and standard error) within each trial at each treadmill speed. The data were binned in 1.0 m/s intervals.