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

Objective: We 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. Methods: Six healthy adults and five chronic complete SCI subjects received vibratory stimulation of their tibia over three different gravitational accelerations (0.3. g, 0.6. g, and 1.2. g) 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. Results: H-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. Conclusions: Vibration 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. Significance: Limb segment vibration may offer a long term method to reduce spinal reflex excitability after SCI.