Vibration alters human sensory motor performance. Changes in the excitability of spinal reflex mechanisms may be responsible for the majority of the observed alterations. We studied the differential effects of vibration locally applied to gastrocnemius soleus and tibialis anterior muscles separately and to both muscles simultaneously. From the results, it is deduced that combined agonist and antagonist muscle vibration may lead to summative interaction between pre- and postsynaptic inhibition at motoneuronal level. Whole-body vibration is taken to mean a combination of synchronous vibrations applied locally and simultaneously to several muscles. The results also demonstrate that the level of inhibition of the H-reflex resulting from the vibration is directly related to the displacement amplitude of the vibration, regardless of the frequency.