Modifications of the Stabilogram during Upright Standing Posture under Conditions of Inclines of the Support Surface

Abstract

Using a stabilographic technique and spectral analysis of stabilograms, we studied changes in the coordinates of the center of feet pressure (CFP) during upright (orthostatic) standing under conditions of a horizontal position of the support surface (SSH) and static inclinations of the latter by 8.5 deg within the sagittal plane (toes up or toes down with respect to the heels, TU and TD, respectively); a group of 14 volunteers was examined. The tests were carried out with the eyes open and closed (EO and EC, respectively). Forward/backward (Y) and lateral (X) shifts of the CFP were analyzed. Upon both EO and EC, the TU position induced forward shifts of the CFP, while the TD position resulted in backward shifts of the latter with respect to its position under SSH conditions (P < 0.001). Such changes of the CFP coordinates are manifestations of the adaptational compensatory postural rearrangements. Under EC conditions, increases in the spectral powers (SPs) of both Y and X body oscillations within a few frequency ranges of the stabilogram were observed in all three positions of the support surface; the spectral profile of such changes depended on the position of the latter. In turn, differences between the spectral indices of postural oscillations upon different inclinations of the support surface depended on the presence or absence of visual afferentation (EO or EC). For example, a higher SP of X oscillations under TU conditions, as compared with the SP of such oscillations under SSH-EC conditions, was found within the 3-6 Hz range but not within the 0.2-0.5 Hz range, as was observed under EO conditions. The TU inclination was accompanied by higher SPs of X oscillations and lower SPs of Y oscillations, as compared to those under TD conditions, and the spectral profile of such differences also depended on the conditions of visual control. In the case of inclinations of the support surface, the power of lateral (X) stabilographic oscillations noticeably increased, while the reaction of Y oscillations related to transition from EO to EC weakened. The results of analysis of spectral characteristics of the staboligram under different conditions of visual control and variations of the support surface position agree with the statement that there is significant interaction between vestibular, proprioceptive, and visual afferentation influencing both forward/backward and transverse oscillations of body sway in the upright posture.