Muscle Stimulation via Whole Body Vibration for Postural Control Applications

Abstract

Although the ability to balance might feel effortless to the most, it should not be given for granted as even the normal process of ageing can compromise it, jeopardising people physical independence. It is therefore important to implement safe training routines that ultimately improve postural control strategies. We evaluated the suitability of whole body vibration (WBV) training –which induces muscle contraction via the stimulation of muscle spindles - for postural control applications. First, we tested the efficacy of different combinations of stimulation frequency and subjects’ posture in eliciting a response from those muscles that play a key role for the implementation of postural responses. Each combination was evaluated by jointly measuring the resulting muscular activation and soft-tissue displacement. Then, we investigated how the selected WBV stimulation affected the balance of healthy subjects. We evaluated the latter by analysing centre of pressure trajectories, muscle and cortex activation and their respective interplay. We found that high frequency vibrations, delivered to participants standing on their forefeet, evoked the greatest contraction of the plantarflexors. Undisturbed balance recorded after such stimulation was characterised by an increased sensitivity of muscle spindles. In line with the latter, the communication between the periphery and the central nervous system (CNS) increased after the stimulation and different muscle recruitment patterns were employed to maintain balance. On the posturography side, stability was found to be compromised in the acute term but seemed to have recovered over a longer term. Together, these findings suggest that, if appropriately delivered, WBV has the potential to stimulate the spindles of the plantarflexors. By doing so, vibration training seems to be able to augment the communication between the proprioceptive organs and the CNS, on which the system relies to detect and react to perturbations, leading to sensorimotor recalibration.