Depression of involuntary activity in muscles paralyzed by spinal cord injury

Abstract

Involuntary muscle contractions are common after spinal cord injury (SCI). Increased sensitivity to Ia muscle afferent input may contribute to the development of these spasms. Since tendon vibration results in a period of postactivation depression of the Ia synapse, we sought to determine whether Achilles tendon vibration (80 HZ for 2 s) altered involuntary contractions evoked by superficial peroneal nerve (SPN) stimulation (5 pulses at 300 HZ) in paralyzed leg muscles of subjects with chronic (>1 year) SCI. Responses to SPN stimulation that were conditioned by vibration were reduced in 66% of trials (by 33+/-12% in tibialis anterior and 40+/-16% in soleus). These reductions in electromyographic activity are unlikely to be mediated by changes at the Ia synapse or motoneuron because vibration did not alter the magnitude of the soleus H reflex. The electromyographic reductions may involve long-lasting neuromodulatory effects on spinal inhibitory interneurons or synapses involved in the flexor reflex pathway. Vibration-evoked depression of electromyographic activity may be clinically useful in controlling involuntary muscle contractions after SCI.

Gravitational force modulates muscle activity during mechanical oscillation of the tibia in humans

“…After incomplete SCI, direct vibration of tendon or of a muscle belly facilitates muscle contraction (Cotey et al, 2009) and WBV training has recently been shown to augment gait (Ness and Field-Fote, 2009). In complete SCI however, prolonged application of vibration to tendon appears to inhibit electromyographic activity of plantar flexor muscles (Butler et al, 2006). This finding is congruent with the blunted EMG response of SCI subjects to whole limb oscillation in the present report.…”

Characteristics of Lower Extremity Clonus after Human Cervical Spinal Cord Injury

“…One interpretation of these results is that stronger muscle activity extraneous to the triceps surae somehow inhibits the soleus motoneurons involved in clonus. Inhibition from ipsilateral and interlimb sources presumably involves many interneurons that act directly to inhibit the soleus motoneurons or to increase inhibition of afferents acting on the triceps surae (Butler et al, 2006;Li et al, 2004b;Pierrot-Deseilligny and Burke, 2005;Zehr and Duysens, 2004;Zijdewind and Thomas, 2001). Consistent with this idea, vibration of the triceps surae tendon depressed clonus in multiple muscles (Butler et al, 2006).…”

“…Inhibition from ipsilateral and interlimb sources presumably involves many interneurons that act directly to inhibit the soleus motoneurons or to increase inhibition of afferents acting on the triceps surae (Butler et al, 2006;Li et al, 2004b;Pierrot-Deseilligny and Burke, 2005;Zehr and Duysens, 2004;Zijdewind and Thomas, 2001). Consistent with this idea, vibration of the triceps surae tendon depressed clonus in multiple muscles (Butler et al, 2006). Furthermore, local commissural interneurons can act on 1a afferents presynaptically, and on motoneurons directly to inhibit extensor motoneurons (Kiehn, 2006), a possible mechanism to explain short clonus when contralateral muscles are activated.…”

Comparison of Single-Session Dose Response Effects of Whole Body Vibration on Spasticity and Walking Speed in Persons with Spinal Cord Injury

“…Prior studies of individuals with spasticity have hinted at mechanisms that may underlie the influence of WBVon spasticity. Tendon vibration is associated with a reduction in involuntary muscle contractions, an effect which is attributed to long-lasting presynaptic inhibitory effects on spinal Ia circuits [27]. These presynaptic inhibitory effects are elicited with tendon vibration frequencies of 40 Hz and higher [28], with 80-100 Hz frequencies being common in electrophysiological studies of presynaptic inhibition.…”