Nonlinear Dynamical Measures in Assessing the Function of Plantar Tactile Feedback on Postural Sway During Quiet Standing Without Vision.

This study aimed to use nonlinear dynamical measures to examine the function of plantar tactile feedback during quiet standing without vision in order to elucidate the stimulation effects on postural sway. Detrended fluctuation analysis, sample entropy, and rambling and trembling analysis were applied to analyze the dynamics of postural sway in the anterior-posterior and mediolateral directions. Twenty young adults stood on a force plate with eyes closed for 35 s under three conditions: no plantar stimulation, plantar stimulation under the forefoot, and plantar stimulation under the midfoot (MS). The results showed that postural dynamics were affected by the placement of plantar stimulation in the absence of visual information. In the anterior-posterior direction, increased detrended fluctuation analysis values for the center of pressure and rambling displacements were revealed in the MS condition than in the plantar stimulation under the forefoot condition, indicating greater adaptability in postural sway. There were also increased detrended fluctuation analysis values in the rambling displacement in the MS condition compared with the no plantar stimulation condition. In the mediolateral direction, the sample entropy in the trembling displacement was significantly greater in the MS condition than in the no plantar stimulation condition, indicating more automaticity in postural sway. These results suggest that plantar stimulation may contribute to balance regulation in an axis- and component-specific manner during quiet standing without vision.