The characteristics of EMG structure are studied for the voluntarily contracting human m. soleus against the background of vibrational stimulation. Averaging over the vibration cycle and spectral analysis are used. Averaging reveals EMG nonuniformity over the cycle; narrow peaks appear in the spectrum at the vibration frequency. EMG analysis proves informative at high vibration frequencies (70-120 Hz), while analysis of the rectified EMG proves informative at low frequencies (30-70 Hz). In the case of tibial ischemic blockade the peak disappears earlier than the tendon reflex. As the force increases, the peak amplitude normalized to the EMG power decreases. The peak rises with prolonged contraction under vibration. These effects are thought to reflect the changes in the relative contribution to the stimulating influx to the motoneurons of the part which is delivered via short connections from the muscle receptors.