OBJECTIVE: To measure the effects of manual segmental vibration (MSV) on motoneuron pool excitability.

METHODS: Seven healthy subjects were tested under five conditions: pretest, upholding static knee position (USKP), MSV, posttest 1 and posttest 2. Each test lasted 2 min, and a 2-min rest was given between pretest, USKP and MSV, whereas the last two tests were consecutive. Cutaneous pressure and vibration frequency were stabilized through training periods. The effects of MSV on motoneuron excitability were investigated by measuring the H-reflex peak-to-peak amplitude.

MEASURES: The H-reflex and M response were taken from the medial gastrocnemius electromyogram and elicited every 7 sec by a 1 ms square wave pulses to the tibial nerve. Fifteen trials were recorded for each condition. Stimulation intensity was set at 10% (+/- 2.5%) of Mmax stimulus.

RESULTS: Repeated-measures analysis of variance comparing conditions revealed no significant differences in M response [F(4,24) = 2.37, p > .05, beta = .35]. H-reflex comparisons revealed significant differences [F(4,24) = 30.39, p < .05, beta = .01] between conditions. Duncan post hoc analysis showed that MSV produced the greatest inhibition (decreases 95%) and USKP also elicited a significant inhibition (decreases 41%).

CONCLUSIONS: The inhibition may be the result of the following mechanisms: the reflex inhibition, the implication of cutaneous afferences and the higher control mechanism. Because MSV produces a reduction in neuromuscular excitability, it could also play a role in predisposing the system for changes to occur and therefore be used as an adjunct for other therapeutic applications.

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