Contribution of the tonic vibration reflex to muscle stress and muscle fatigue.

The aim of the investigation was to determine the influence of vibration displacement amplitude (200, 300 microns peak-to-peak), as opposed to acceleration effects at selected frequencies (40, 80, 100, 120, 150, 200 Hz), on a commonly observed but often undesired motor response elicited by local vibratory stimulation, that is, the tonic vibration reflex (TVR). Vibration was applied to the distal tendons of the hand flexor muscles. Changes in the activity of hand flexor and extensor muscles were analyzed as a function of both their initial contraction level (0, 10, 20% of maximal voluntary contraction) and the vibration parameters. The main results indicate that TVR increases with the initial muscle contraction and increases with vibration frequency up to 100-150 Hz but decreases beyond. High-frequency vibration seems to induce less muscle and tendon stress. This result is particularly important for the design of handheld vibrating tools.