Overground walking with a robotic exoskeleton elicits trunk muscle activity in people with high-thoracic motor-complete spinal cord injury

Abstract

Background: The trunk muscles are critical for postural control. Recent neurophysiological studies have revealed sparing of trunk muscle function in individuals with spinal cord injury (SCI) classified with thoracic or cervical motor-complete injuries. These findings raise the possibility for recruiting and retraining this spared trunk function through rehabilitation. Robotic gait training devices may provide a means to promote trunk muscle activation. Thus, the objective of this study was to characterize and compare the activation of the trunk muscles during walking with two robotic gait training devices (Ekso and Lokomat) in people with high thoracic motor-complete SCI.

Methods: Participants with chronic motor-complete paraplegia performed 3 speed-matched walking conditions: Lokomat-assisted walking, Ekso-assisted walking overground, and Ekso-assisted walking on a treadmill. Surface electromyography (EMG) signals were recorded bilaterally from the rectus abdominis (RA), external oblique (EO), and erector spinae (ES) muscles.

Results: Greater recruitment of trunk muscle EMG was elicited with Ekso-assisted walking compared to the Lokomat. Similar levels of trunk EMG activation were observed between Ekso overground and Ekso on the treadmill, indicating that differences between Ekso and Lokomat could not be attributed to the use of a hand-held gait aid. The level of trunk EMG activation during Lokomat walking was not different than that recorded during quiescent supine lying.

Conclusions: Ekso-assisted walking elicits greater activation of trunk muscles compared to Lokomat-assisted walking, even after controlling for the use of hand-held assistive devices. The requirement of the Ekso for lateral weight-shifting in order to activate each step could lead to better postural muscle activation.

Keywords: EMG; Exoskeletons; Spinal cord injury; Trunk muscles.

Fig. 1

Trunk muscle EMG activity during maximum voluntary contractions. Filtered and rectified EMG activity recorded from the trunk muscles during the maximum voluntary contraction (MVC) trials in each SCI subject (black) and a representative able-bodied subject (C8) (grey). SCI subjects are plotted in sequence from left to right according to their injury level from highest to lowest. R/L = right/left, RA = Rectus Abdominis, EO = External Oblique, and ES = Erector Spinae. (Left ES data was not available from subject S03 due to technical error)

Fig. 2

Trunk muscle activation patterns during robotic-assisted walking in able-bodied and SCI subjects. a) Mean trunk muscle activity patterns averaged across able-bodied participants during walking on treadmill with an average speed of 1.2 km/h. b) Mean trunk muscle activity patterns averaged across able-bodied participants during walking in the Lokomat (Loko-TM), Ekso on treadmill (Ekso-TM) and Ekso overground (Ekso-OG) with an average matched speed across conditions of 1.26 km/h. All plots represent the mean trunk muscle activity normalized to 100% of the gait cycle (n > 20 steps each plot for each subject). Grey shaded areas in each plot represent baseline EMG activity recorded in supine position (BAS). c) Mean trunk muscle activity patterns averaged across all SCI subjects during the same walking conditions with an average matched speed across conditions of 1.16 km/h. RA = Rectus Abdominis, EO = External Oblique, and ES = Erector Spinae

Fig. 3

Trunk muscle EMG amplitudes across baseline and walking conditions. Comparison of EMG amplitude recorded during quiet supine lying and robot-assisted walking conditions. The average RMS EMG amplitude in rectus abdominis (a) external oblique (b), and erector spinae (c) during quiet supine lying (BAS), Lokomat-assisted walking (Loko-TM), Ekso on the treadmill (Ekso-TM) and Ekso overground walking (Ekso-OG) are plotted for each SCI participant (represented by different coloured circles). Grey bars represent the RMS EMG amplitude averaged across all SCI participants and error bars represent the standard deviation. Values from left and right homologous muscles were expressed as % MVC and summed bilaterally. * = p < 0.0125

Fig. 4

Trunk muscle activity normalized to gait cycle and breathing cycle. SCI subject (S05) average trunk muscles activity (Rectus Abdominis (RA), external oblique (EO) and erector spinae (ES)) normalized to the gait cycle (a) vs. normalized to the breathing cycle (b) during Ekso-TM

Fig. 5

Total acceleration of the trunk across robotic-assisted walking conditions. a) Mean total acceleration of the trunk for all SCI subjects across the 3 robotic-assisted walking conditions: Lokomat (Loko-TM), Ekso on treadmill (Ekso-TM) and Ekso overground (Ekso-OG). b) Total medial-lateral trunk acceleration during the same walking conditions. * = p < 0.001