Motor strategies responsible for maintaining standing posture after deafferentation of the unilateral leg.

OBJECTIVE: To identify the motor strategies responsible for maintaining standing posture after deafferentation of the unilateral leg. DESIGN: Pretest-posttest, repeated-measures design. SETTING: A Japanese university hospital rehabilitation facility. PARTICIPANTS: Nine healthy subjects aged 25 to 32 years. INTERVENTION: Two separate sessions that consisted of prolonged standing (control task) and standing until the H-reflex disappeared through the application of an inflated pneumatic cuff above the right knee. MAIN OUTCOME MEASURES: Center of pressure (COP), hip and ankle joint positions, and electromyographic activities. RESULTS: In the control task, no time-related change during prolonged standing was found in any of the measured parameters. After deafferentation, the right soleus activity decreased significantly (P<.01), so the mean velocities of the COP in the anteroposterior and mediolateral directions were greater and the average COP position under the right foot shifted backward compared with those in the previous periods (P<.01). Also, the left tibialis anterior and soleus were activated, as was the bilateral gluteus medius. CONCLUSIONS: The unilateral loss of leg and foot sensory information necessitated additional regulatory activities to stabilize the standing posture. The newly organized posture appeared to partly simulate the standing posture in patients with sensory disturbance of a unilateral leg.