*2.1.3. Neurophysiological mechanism*

Muscle spindle senses a very small change in muscle length when a skeletal muscle receives vibration stimulation. And this information is transmitted to the fibers of group Ia or II, eventually to reach the spinal cord. In the spinal cord, the information serves as presynaptic inhibition through an interstitial cell and suppresses the alpha motor neuron (Gillies 1969, Shinohara 2005).

In addition, sustained vibration stimulation will selectively excite group Ia fibers. That will then bring about, in nerve endings, depletion of neurotransmitters and a rising threshold of group Ia fibers (Kouzaki 2000). It is believed that this is one of the reasons why a decrease is observed in the excitability of motor neurons in the spinal cord.
