Withdrawal Reflexes Elicited by Electrical Stimulation of the Foot Sole during Gait

A technique of distributed surface electrical stimulation of the foot sole was used to elicit the withdrawal reflex in ankle flexors and extensors during gait. Tibialis anterior and soleus reflexes were recorded from 8 subjects during treadmill walking. The largest responses in tibialis anterior were evoked at the arch of the foot, while in soleus the largest responses were elicited at the heel/arch of the foot. Reflexes were elicited in four different phases of the gait cycle (after heel-contact, in the flat-foot phase, after heel-off and in the swing phase). The strongest tibialis anterior reflexes were obtained when stimulating after heel-contact. The soleus reflexes were minimum when stimulation was applied after heel-off. Spinal motor centers most likely modulate the withdrawal reflexes in order to secure balance and continuity of the movement. The reflex may have application for initiation of gait in paraplegic patients.