Human vibration upside down or two faces of Janus Seminar

Almost half a century ago A. Berthoz suggested that three frequency ranges should be considered in human vibration: the low, middle and high range to distinguish dominating mechanisms underlying the effects. The work presented will primarily pertain to the high frequency range (> 20 Hz) to illustrate two faces of mechanical vibration. This mechanical action applied to human tissues activates sensory mechanoreceptors, which contributes to the alteration of sensory information, perception and muscle/movement control. For example hand vibration can lead to motor unit synchronization and exacerbate muscle fatigue, considered a precursor of musculoskeletal disorders. Furthermore, tactile vibration can lead to a decrease in pain perception, postural reorganization or, when considered as an alarm, may promote the immediate recall of a motor program to recover from a fall. While whole body vibration exposure results in several health issues it also contributes to complex movement alterations strongly dependent on frequency, which makes the development of an active biodynamic model a headache. The mechanisms underlying the diverse phenomena will be discussed.