Vibration is a form of afferent input known to influence the activity of spinal neural circuits. In individuals in whom neuropathology has disrupted the communication between the brain and spinal cord, vibration may mimic some functions formerly served by the lost or impaired supraspinal inputs. In individuals with SCI, vibration may influence spinal neural circuits in a manner that results in more normal reflex modulation and improved walking function. Three experiments were performed to assess the effects of vibration on spinal locomotor-generating circuitry, spinal reflex activity, and walking function.
In Experiment 1, localized leg vibration was used to elicit air-stepping responses in the lower extremities. We compared responses of individuals with SCI to those of non-disabled (ND) individuals, assessed the influence of severity of SCI, and assessed the influence of locomotor training on the air-stepping response in individuals with SCI. Our results indicate that vibration of the tensor fascia latae elicited more robust and consistent responses than did vibration of the quadriceps or hamstrings muscles. Individuals with SCI had less consistent and less robust responses than ND individuals. In those with SCI, neither severity of injury nor locomotor training influenced the robustness or consistency of the response.
In Experiment 2, we investigated the effect of whole-body vibration (WBV) on spasticity, as measured by spinal stretch reflex (SSR) excitability, in individuals with SCI. We also assessed differences in the influence of WBV among individuals who used antispastic medications and those who did not. Subjects were tested before and after participation in a 3 day/week, 12-session WBV intervention. There was a significant reduction in spasticity that persisted for several days following the WBV intervention. The amount by which spasticity was reduced was not different in those who used antispastic agents compared to those who did not use these agents.
In Experiment 3, we assessed the effects of the 12-session WBV intervention on walking function. WBV was associated with significant increases in walking speed, cadence, step length of the stronger leg, and consistency of hip-knee intralimb coordination. Increases in cadence and stronger-leg step length were correlated with improvements in walking speed.
These results suggest that WBV may represent an approach to decreasing spasticity, and may be useful for individuals in whom spasticity interferes with function. Furthermore, vibration appears to have a beneficial effect on walking function, perhaps by influencing spinal locomotor-generating circuitry.