 - Homosynaptic depression HD: the HD will be obtained through a serie of two consecutive stimuli separated by a interstimulus interval from 30ms until 10.000ms. The stimuli will be delivered on popliteal fossa and the electromyographic responses from soleus muscle will be recorded. The stimuli will be delivered with the intensity necessary to produce the maximal H reflex this information will be available in the recruitment curve as stated before. The difference between the first and the second stimuli for each interstimulus interval will give rise to the recovery curve. 