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

Abstract

Introduction Recent investigations suggest that whole-body vibration (WBV) training contributes to enhanced athletic performance2,4 and improvement in functional ability in individuals with disabilities1,3, yet the neurophysiological basis for these observed benefits has not been investigated. Whole-body vibration is thought to elicit muscular activity via stretch reflexes2,4. The subject stands on a platform that applies vertical sinusoidal vibration to the body and stimulates sensory receptors, specifically the muscle spindles. Muscle spindle activation results in reflex activation of the alpha-motoneurons thereby generating muscle contractions. The spinal stretch reflex and its electrical analog, the H-reflex, are monosynaptic reflexes that participate in a wide range of human motor behaviors5. 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. Modulation of spinal reflexes is necessary for normal motor performance and locomotor control6. It is known that modulation of the H-reflex is altered after neurological injury7. Therefore, modulation of the H-reflex by WBV would have clinical implications for use in the rehabilitation setting to improve functional performance. The purpose of this study is to determine the acute effects of WBV training on the soleus H-reflex in able-bodied subjects.