Decrease of motoneuron excitability during stretching of the human soleus

Changes of motoneuron (MN) excitability was studied during the basic modalities of slow or static stretching of the human soleus muscle (Sol). Tendon (T) and Hofmann (H) reflexes were recorded during slow passive (assisted) stretching (SS). The H response was analysed in SS, in SS preceded by a maximal isometric contraction of the muscle or contraction-relaxation (CR) and during stretching of the muscle by contracting the antagonistic muscle (AC). The maximal joint mobilization during SS, CR and AC appears to be closely related to the decrease of the H response. It is suggested that the joint mobilization during slow stretching is closely controlled by the level of inhibition of the MN pool excitability, which lasts only as long as the stretching manoeuvre is maintained.