Acute Effects of Whole-Body Vibration on Soleus H-Reflex

Abstract

2382 INTRODUCTION: Recent investigations suggest that whole-body vibration (WBV) training contributes to improved athletic performance. Yet, the neurophysiological basis for these observed benefits has not been investigated. The soleus H-reflex is a reliable and well-studied indicator of lower limb spinal reflex activity. The H/M ratio (motor response from Ia sensory fibers/direct motor response) is used as an index of efficacy of transmission between the Ia sensory fiber and the alpha motor neuron. PURPOSE: To determine the acute effects of WBV training on the soleus H-reflex in able-bodied subjects. METHODS: Ten healthy subjects participated in this preliminary study. Subjects underwent soleus H-reflex testing of their right lower extremity, which consisted of measuring their maximum H-reflex and maximum M-wave in sitting. The subjects then stood on a WBV platform (Galileo) for five minutes at 26 Hz. Seated H-reflex testing was repeated immediately following the training session. Pre- and post-test values of maximum H-wave amplitudes and H/M ratios were compared using repeated measures ANOVA. RESULTS: A statistically significant decrease in maximum H-reflex amplitude (mean = 25%) was observed (p<0.05) following five minutes of WBV. No statistically significant change was detected in maximum Mwave. Following WBV training, there was a statistically significant (p<0.05) decrease in the H/M ratio from 51% to 40%. CONCLUSION: The results of this preliminary study suggest that changes to spinal Ia excitability occur acutely after WBV. Vibration is known to have an effect on presynaptic Ia inhibition, making this a likely mechanism for the observed change in H-reflex amplitude. Further studies must be conducted to examine, in more detail, the neurophysiological mechanisms that contribute to this effect, and to understand the neural basis for the reported functional benefits resulting from WBV.