Long latency response in soleus muscle evoked by magnetic stimulation at the foramen magnum

We performed magnetic stimulation at the level of foramen magnum in healthy subjects to evaluate the long latency response in lower limb muscle. Subjects assumed an upright stance and we recorded electromyographic activities in soleus muscle. A late response at the onset latency of approximately 40 ms was elicited. The late response wasn't induced in other lower limb muscles; anterior tibial muscle, quadriceps femoris muscle, and biceps femoris muscle. Additionally, magnetic stimulation to foot motor cortex, basal occiput and cervical nerve roots did not evoke the response with latency of 40 ms. These results reveal the late response in soleus muscle that has not been previously reported. We speculate that it is involved with the long-loop reflex.