Rhythmic arm cycling suppresses hyperactive soleus H-reflex amplitude after stroke

Area of Science:

• Neuroscience
• Rehabilitation Medicine
• Motor Control

Background:

• Rhythmic arm cycling movement is known to suppress soleus H-reflexes in neurologically intact individuals.
• This suppression effect is frequency-dependent, increasing with higher movement rates.
• The potential for using arm cycling to reduce exaggerated reflexes, like spasticity, post-stroke is being explored.

Purpose of the Study:

• To investigate if the H-reflex suppressive effect of rhythmic arm cycling is maintained in individuals who have experienced a stroke.
• To test the hypothesis that the suppressive effect of arm cycling on leg H-reflexes is partially retained after stroke, possibly due to preserved subcortical and spinal mechanisms.

Main Methods:

• Participants with chronic stroke performed rhythmic arm cycling at two frequencies: approximately 1 Hz and their maximum possible frequency (approximately 1.5 Hz).
• Soleus H-reflexes were simultaneously recorded in both the more and less affected legs.
• Full recruitment curves for H-reflexes were obtained during arm cycling to quantify the suppressive effect.

Main Results:

• Arm cycling significantly suppressed soleus H-reflex amplitudes in both legs of stroke participants.
• The degree of H-reflex suppression observed in stroke survivors was less pronounced compared to neurologically intact and age-matched control subjects.
• This indicates that while the suppressive pathway remains accessible, its efficacy is diminished post-stroke.

Conclusions:

• Neural pathways activated by arm cycling can still influence spinal reflex mechanisms in the legs after stroke.
• The findings support the concept that interlimb communication and spinal control mechanisms contribute to H-reflex modulation post-stroke.
• The suppressive effect of arm cycling on H-reflexes holds potential for therapeutic applications in modifying exaggerated reflexes and spasticity in stroke rehabilitation, though further research is needed to confirm its clinical impact.