Reflex reciprocal facilitation of antagonist muscles in spinal cord injury.
METHODS
Electromyographic study in complete and incomplete spinal cord injury (SCI).


OBJECTIVE
To examine the changes in the pattern of reciprocal inhibition between agonist and antagonist muscles in SCI.


METHODS
Sensory Motor Performance Program, Rehabilitation Institute of Chicago, IL, USA.


METHODS
Tendon taps were delivered manually with an instrumented hammer to the tendons of the tibialis anterior and soleus muscle in positions of full-ankle dorsiflexion and plantarflexion in eight subjects with complete SCI and eight subjects with incomplete SCI. Electromyographic activity (EMG) was recorded from ankle dorsiflexor and plantarflexor muscles. Tapping force was also recorded by a force sensor mounted to the tendon hammer, indicating the stimulus onset. Measures of reflex EMG magnitude and reflex latency were obtained for both agonist and antagonist muscles. The ratio of antagonist to agonist EMG was computed based on normalized EMG.


RESULTS
Substantial reflex responses occurred in both the stretched muscle and in its antagonist. The reflex in antagonist, which we term 'reciprocal facilitation (RF)', was most evident in subjects with incomplete SCI. The magnitude of RF was consistently greater than reflex responses in agonist muscles under all test conditions. The latency of the RF was comparable to that of monosynaptic reflex response.


CONCLUSIONS
Following SCI, reciprocal organization of segmental reflexes at the ankle is often partially or completely suppressed, allowing reflex activation in antagonist muscles to be manifested. Possible mechanisms underlying these changes in neural organization are discussed.


BACKGROUND
This study was supported by Spinal Cord Research Foundation, the Paralyzed Veterans of America.
Department of Physical Medicine and Rehabilitation, Northwestern University, Chicago, IL, USA.
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D000328:Adult; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D009470:Muscle Spindles / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation / Q000503:physiopathology*; D009433:Neural Inhibition / Q000502:physiology*; D010243:Paralysis / Q000503:physiopathology*; D011930:Reaction Time / Q000502:physiology; D012018:Reflex / Q000502:physiology*; D012026:Reflex, Stretch / Q000502:physiology; D013119:Spinal Cord Injuries / Q000503:physiopathology*