Soleus H-reflex phase-dependent modulation is preserved during stepping within a robotic exoskeleton

Area of Science:

• Neuroscience
• Biomechanics
• Robotics

Background:

• The soleus H-reflex exhibits phase-dependent modulation during human locomotion, reflecting spinal cord circuitry.
• Robotic exoskeletons are increasingly used for gait rehabilitation, but their effect on spinal reflex modulation is not fully understood.

Purpose of the Study:

• To investigate the preservation of soleus H-reflex modulation during robotic exoskeleton-assisted stepping.
• To determine the influence of different body weight support (BWS) levels on this modulation.

Main Methods:

• Healthy subjects performed robotic-assisted stepping with 25% and 50% BWS.
• The soleus H-reflex was elicited via posterior tibial nerve stimulation and normalized to maximal M-waves.
• Electromyographic (EMG) activity and H-reflex gain were analyzed across the step cycle.

Main Results:

• The phase-dependent modulation of the soleus H-reflex was preserved during robotic-assisted stepping at both 25% and 50% BWS.
• A linear relationship between H-reflex amplitude and soleus EMG was observed, with reflex gain remaining constant.
• EMG amplitudes were lower at 50% BWS compared to 25% BWS.

Conclusions:

• Body unloading, reduced EMG, and decreased ankle movement do not impede the manifestation of soleus H-reflex phasic excitability.
• Spinal interneuronal circuits involved in H-reflex modulation are engaged physiologically during robotic-assisted stepping, suggesting potential benefits for gait rehabilitation in neurological disorders.