Effect of plantar desensitization on postural adjustments prior to step initiation

Plantar cutaneous afferent provides information about the contact between the body and the support surface and could affect the anticipatory postural adjustments (APAs). This study investigated the effect of plantar desensitization on the APAs for step initiation. Twenty-five healthy young adults participated in this study and were instructed to begin walking as fast as possible under 4 plantar desensitization conditions, none (NoneD), and desensitization of the stepping, supporting or bilateral (BilD) plantar surfaces, with eyes open or closed. The desensitization was achieved by cold water immersion of the plantar surface for 15 min. Foot switches recorded the timing of the stepping events. Surface electromyography (EMG) recorded the activation of bilateral tibialis anterior. The center of pressure (COP) and ground reaction force (GRF) data were derived from the force platform on which the subject initiated walking. The results showed that during the anticipation phase, the peak COP displacement toward the stepping leg was significantly smaller in BilD than in unilateral desensitization, which in turn was smaller than in NoneD, regardless of vision. The time to reach the peak COP displacement was significantly sooner with plantar desensitization in the eyes open condition. The GRF, EMG and anteroposterior COP displacement or the timing of the stepping events was not affected by plantar desensitization. These findings indicate that plantar cutaneous afferent contributed to the control of the APAs for step initiation by scaling the displacement of the mediolateral COP displacement and loss of its sensitivity could not be compensated by visual inputs.