Force and displacement-controlled tendon vibration in humans.

This study investigated how the mechanical characteristics of tendon vibration influence the responses of human muscle receptors. In this study, we used a tendon vibrator in which the force, displacement and frequency of vibration were precisely controlled. The tendon vibrator could produce large amplitude displacements, so it was also used to impose ramp-and-hold stretches to the tendon to help classify muscle spindle afferents. In normal human subjects, we recorded microneurographically from single muscle afferents during tendon vibration to determine how afferent responses are influenced by the force and the displacement applied to the tendon and how these influences of force and displacement change with vibration frequency. Our results indicate that the sensitivity of muscle spindle afferents to tendon vibration is enhanced by increasing force and displacement and decreased by increasing frequency. It is concluded that, in order to predict the afferent response to vibration, the mechanical characteristics of tendon vibration must be controlled. Controlling the mechanical characteristics of tendon vibration and understanding the effect of vibration on afferent discharge will be useful for furthering our understanding of the peripheral control of movement.