Responses to three vibratory bursts either alone or alternated with trains of electrical stimulation. A) Plantarflexion torque (seven superposed recordings) and EMG from the soleus muscle (typical recording) in response to three 2-s vibratory bursts (100 Hz sinusoidal waves) separated by 2 s resting periods (no stimulation). The inset of the figure highlights the soleus EMG (black line) and the evoked plantarflexion force (gray line) on an expanded time scale (the two arrows indicate, respectively, the initiation of vibration and the monosynaptic response triggered by the first cycle of the vibratory stimulus). B) Plantarflexion force (seven superposed recordings) in response to three 2-s vibratory bursts (100 Hz sinusoidal waves) alternately applied with 20-Hz electrical stimulation (starting with 2s and terminating with 23 s of electrical stimulation). The two approximately constant responses (control values of force) correspond to the plantarflexion force evoked by 37 s of 20 Hz electrical stimulation alone (control stimulation).