Changes in motor activity and biomechanics during balance recovery following cutaneous and muscular deafferentation

The effects of lower limb deafferentation were examined during execution of a balance recovery step following a forward fall induced by release of an initial inclined posture. The subjects were healthy control subjects and patients with a unilateral loss of the Achilles tendon reflex following S1 radiculitis. Deafferentation of healthy subjects was obtained by unilateral leg ischemia (four subjects) and by foot anesthesia (five subjects). The balance recovery step was characterized by the surface electromyographic (EMG) activity of right and left soleus and tibialis anterior muscles and the kinetics of the center of gravity and center of foot pressure. Experimentally induced and pathological deafferentation decreased the EMG activity of the ipsilateral soleus and lowered the vertical ground reaction force. The lower limb motor activity was more affected by loss of muscle proprioceptive afferents than by loss of plantar cutaneous afferents. Patients showed early and bilateral changes in soleus and tibialis activities, whichever side was affected. The step length of patients was also shorter than that of controls, but it remained similar before and after deafferentation in the healthy subjects. The results are discussed in terms of ipsilateral and crossed pathway connections and functional adaptive strategies.