Reflex reciprocal facilitation of antagonist muscles in spinal cord injury

Abstract

Study Design: 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. Settings: 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.

Spastic Reflexes Triggered by Ankle Load Release in Human Spinal Cord Injury

“…Activation of the tibialis anterior in synchrony with the ankle plantar flexors during clonus has also been observed by others (Beres-Jones et al 2003;Hidler and Rymer 2000) and appears to be a common feature of clonus. The simultaneous activation of the tibialis anterior may be associated with a reciprocal facilitation during stretch of the plantar flexors, as has been reported during tendon taps of the Achilles tendon (Xia and Rymer 2005). Again, activation of this reflex pathway did not appear to extend to the hip triggered reflex because the thigh muscles were relatively unaffected by the clonus in the ankle.…”

Up-regulation of 5-HT2 receptors is involved in the increased H-reflex amplitude after contusive spinal cord injury

“…Furthermore, the stimulation of the tibial nerve at the ankle allows for the plantar muscles to be isolated as much as possible without stimulating other muscle groups, thereby reducing the possibility of reciprocal inhibition or facilitation from other muscle groups (Crone, et al, 2003, Okuma, et al, 2002, Xia and Rymer, 2005. It would be interesting to see if our results (physiological as well as immunohistochemical) could be observed in more proximal muscle groups, such as the gastrocnemius or tibialis, which play a more prominent role in locomotion.…”

Activity-Dependent Increase in Neurotrophic Factors Is Associated with an Enhanced Modulation of Spinal Reflexes after Spinal Cord Injury

“…Several explanations were investigated, including increased electrical coupling mediated by gap junctions (Yates et al, 2008a), reciprocal facilitation of antagonistic muscles (Xia and Rymer, 2005), decreased presynaptic inhibition (Hultborn et al, 1996;Reese et al, 2006;SchindlerIvens and Shields, 2000;Thompson et al, 1992), and changes in the persistent inward currents (PICs; Bennett et al, 2001;Hornby et al, 2006). PICs are thought to be involved in the development of spasticity after SCI.…”