Focal muscle vibration: evaluation of physical properties and his applications

Vibration is the sensation produced by sinusoidal oscillation of objects placed against the skin. The vibratory frequency is signaled by the frequency of action potentials fired by the sensory nerves and the total number of active sensory nerves is linearly related to the amplitude of vibration. In the last years many works were done evaluating the different clinical applications of the focal muscle vibration; the aim of this work is to analyze the interaction between the vibratory application and the skin. For this study the apparatus of focal muscle vibration analyzed was firstly calibrated by measuring the actual peak to peak displacement of the tip as a function of the power supplied to the shaker; then were measured the Direct Component (DC) of the force by which the shaker is pushed against the patient’s skin and the Alternate Component (AC). We observed that from displacements imposed by the tip ranging from 0 to about 200 micrometers, the applied load increases monotonically, but non linearly, with the displacement; above this value, any further increase of the peak to peak displacements actually does not lead to an effective increase of the amplitude of the mechanical stimulation. We can conclude that with this focal muscle vibration applied to the muscle we are able to stimulate the spindles that respond to 200 micrometers amplitude that are probably ones able to generate a proprioceptive signal.