Major role for sensory feedback in soleus EMG activity in the stance phaseof walking in man

1. Sensory feedback plays a major role in the regulation of the spinal neur al locomotor circuitry in cats. The present study investigated whether sens ory feedback also plays an important role during walking in 20 healthy huma n subjects, by arresting or unloading the ankle extensors 6 deg for 210 ms in the stance phase of gait. 2. During the stance phase of walking, unloading of the ankle extensors sig nificantly (P < 0.05) reduced the soleus activity by 50% in early and mid-s tance at an average onset latency of 64 ms. 3. The onset and amplitude of the decrease in soleus activity produced by t he unloading mere unchanged when the common peroneal nerve, which innervate s the ankle dorsiflexors, was reversibly blocked by local injection of lido caine (n = 3). This demonstrated that the effect could not be caused by a p eripherally mediated reciprocal inhibition from afferents in the antagonist nerves. 4. The onset and amplitude of the decrease in soleus activity produced by t he unloading were also unchanged when ischaemia was induced in the leg by i nflating a cuff placed around the thigh. At the same time, the group Ia-med iated short latency stretch reflex was completely abolished. This demonstra ted that group Ia afferents were probably not responsible for the decrease of soleus activity produced by the unloading. 5. The findings demonstrate that afferent feedback from ankle extensors is of significant importance for the activation of these muscles in the stance phase of human walking. Group II and/or group Ib afferents are suggested t o constitute an important part of this sensory feedback.