Soleus H-reflex phase-dependent modulation is preserved during stepping within a robotic exoskeleton.
OBJECTIVE
To investigate to what extent the phase-dependent modulation of the soleus H-reflex is preserved when bilateral leg movements are electromechanically driven by a robotic exoskeleton at different levels of body weight support (BWS) in healthy subjects.


METHODS
The soleus H-reflex was elicited by posterior tibial nerve stimulation with a 1-ms single pulse at an intensity that the M-waves ranged from 4% to 9% of the maximal M-wave across subjects. Stimuli were randomly dispersed across the step cycle which was divided into 16 equal bins. At each bin, a maximal M-wave was elicited 100 ms after the test H-reflex and was used to normalize the associated M-wave and H-reflex. Electromyographic (EMG) activity from major hip, knee, and ankle muscles was recorded with surface bipolar electrodes. For each subject and muscle, the integrated EMG profile was established and plotted as a function of the step cycle phases. The H-reflex gain was determined as the slope of the relationship between the H-reflex and soleus EMG amplitudes at 100 ms before the H-reflex for each bin.


RESULTS
During robotic assisted stepping, the phase-dependent soleus H-reflex modulation pattern was preserved and was similar at 25% and 50% BWS, a linear relationship between soleus H-reflex amplitude and background activity was found, and the reflex gain did not change with alterations of the BWS level. EMG amplitudes were smaller at 50% compared to 25% BWS.


CONCLUSIONS
Body unloading, decreased EMG amplitude of ankle extensors, and reduced ankle movement are not key factors for the soleus H-reflex phasic excitability to be manifested.


CONCLUSIONS
Robotic devices are utilized for rehabilitation of gait in neurological disorders. Based on our findings, spinal interneuronal circuits involved in the phase-dependent modulation of the soleus H-reflex will be engaged in a physiological manner during robotic assisted stepping in neurological disorders.
Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, IL, USA. Maria.Knikou@csi.cuny.edu
Maria
M
Knikou
Nupur
N
Hajela
Chaithanya K
CK
Mummidisetty
Ming
M
Xiao
Andrew C
AC
Smith
D000328:Adult; D001835:Body Weight / Q000502:physiology; D003627:Data Interpretation, Statistical; D004525:Efferent Pathways / Q000502:physiology; D004576:Electromyography; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D007395:Interneurons / Q000502:physiology; D008124:Locomotion / Q000502:physiology; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D012371:Robotics; D013116:Spinal Cord / Q000166:cytology / Q000502:physiology; D016138:Walking / Q000502:physiology; D055815:Young Adult