Effects of ankle joint and crural muscle vibrations on standing postural control with eyes-closed inferred from maximum displacements of center of gravity and center of pressure

[Purpose] The aim of the present investigation was to discover which afferent signals (from crural muscle spindle or ankle joint) contribute to dynamic standing postural control. [Subjects] Ten male subjects (23-35 years) stood with eyes-closed on a movable platform. [Methods] Vibrators (92 Hz) were tightly fixed bilaterally to the Achilles and tibialis anterior (TA) tendons or to the lateral and medial malleolies. The maximum displacements and time of center of gravity (COGy) and center of pressure (COPy) of the anterior-posterior axis were examined under control, crural vibration (CV) and malleoli vibration (MV) conditions on the moving platform. [Results] When the platform moved backward, peak times of COGy and COPy in MV were significantly delayed compared to the control condition (p<0.05). The maximum displacement of COGy in MV increased significantly compared to the control condition (p<0.05). When the platform moved forward, peak time of COPy in MV were significantly delayed compared to the control condition (p<0.05). [Conclusion] We think that the afferent signal from the ankle joint rather than the afferent signal from the soleus (Sol) muscle spindle contributed to COGy and COPy displacements when the platform moved backward. We also think that COGy and COPy were controlled by the compensatory activities of other muscles except for TA when the platform moved forward, though TA activity depended on the afferent signal from the ankle joint as well as Sol.