Limb segment vibration modulates spinal reflex excitability and muscle mRNA expression after spinal cord injury

ObjectiveWe investigated the effect of various doses of vertical oscillation (vibration) on soleus H-reflex amplitude and post-activation depression in individuals with and without SCI. We also explored the acute effect of short-term limb vibration on skeletal muscle mRNA expression of genes associated with spinal plasticity.MethodsSix healthy adults and five chronic complete SCI subjects received vibratory stimulation of their tibia over three different gravitational accelerations (0.3g, 0.6g, and 1.2g) at a fixed frequency (30 Hz). Soleus H-reflexes were measured before, during, and after vibration. Two additional chronic complete SCI subjects had soleus muscle biopsies 3 h following a single bout of vibration.ResultsH-reflex amplitude was depressed over 83% in both groups during vibration. This vibratory-induced inhibition lasted over 2 min in the control group, but not in the SCI group. Post-activation depression was modulated during the long-lasting vibratory inhibition. A single bout of mechanical oscillation altered mRNA expression from selected genes associated with synaptic plasticity.ConclusionsVibration of the lower leg inhibits the H-reflex amplitude, influences post-activation depression, and alters skeletal muscle mRNA expression of genes associated with synaptic plasticity.SignificanceLimb segment vibration may offer a long term method to reduce spinal reflex excitability after SCI.

► Vertical limb oscillations (vibration) resulted in a predominant inhibition of H-reflex and post-activation depression mechanism in both SCI and healthy control groups.
► Microarray analysis revealed that a short-term limb segment vibration had significant effects on genes associated with synaptic plasticity.
► These findings highlight the possibility that long-term vibration training may promote spinal neuronal plasticity in individuals with chronic SCI.