After stroke bidirectional modulation of soleus stretch reflex amplitude emerges during rhythmic arm cycling.
OBJECTIVE
after stroke a typical presentation is exaggerated stretch reflexes (SRs) on the more affected (MA) side. The present study evaluated the contribution of presynaptic inhibition (PSI) induced by arm cycling and homosynaptic depression (HD) to the modulation of hyperreflexia at the ankle after stroke. Possible asymmetry of these effects between the MA and less affected (LA) legs was also assessed.


METHODS
soleus SR was conditioned by: arm cycling at 1 Hz (to increase Ia PSI); or, a preceding conditioning tendon tap applied 1 s before the test stimulus (to induce HD). The extent of conditioning effects was compared between the MA and the LA legs.


RESULTS
for both MA and LA legs, rhythmic arm movement induced a bidirectional effect in different participants, either increasing or decreasing SR amplitude (p < 0.05). HD had a significant effect in both legs (p < 0.05), however, the effect of both a previous muscle stretch and arm cycling was not different between the MA and the LA legs.


CONCLUSIONS
our data reveal a bidirectional reflex modulation induced by arm cycling that produced facilitation in some and suppression in other participants after stroke. Relative SR amplitude modulation did not differ between the LA and MA legs. We speculate that alterations in SR amplitude modulation after stroke may reflect specific changes in both presynaptic afferent transmission mechanisms and fusimotor control.


CONCLUSIONS
the present findings open new perspectives on the characterization of pathophysiology of stroke during the performance of functionally relevant motor tasks.
Laboratory of Signal Processing and Motor Control, University of Brasïlia, College of Physical Education Brasïlia, Brazil ; Rehabilitation Neuroscience Laboratory, School of Exercise Science, Physical, and Health Education, University of Victoria Victoria, BC, Canada.
Rinaldo A
RA
Mezzarane
Rehabilitation Neuroscience Laboratory, School of Exercise Science, Physical, and Health Education, University of Victoria Victoria, BC, Canada ; Department of Integrative Physiology, Kyorin University School of Medicine Mitaka, Tokyo, Japan.
Tsuyoshi
T
Nakajima
Rehabilitation Neuroscience Laboratory, School of Exercise Science, Physical, and Health Education, University of Victoria Victoria, BC, Canada ; Human Discovery Science, International Collaboration on Repair Discoveries Vancouver, BC, Canada ; Centre for Biomedical Research, University of Victoria Victoria, BC, Canada ; Division of Medical Sciences, University of Victoria BC, Canada.
E P
EP
Zehr
homosynaptic depression; hyperreflexia; locomotion; presynaptic inhibition; spasticity; spinal cord