Postural stability margins as a function of support surface slopes

This investigation examined the effects of slope of the surface of support (35°, 30°, 20°, 10° Facing(Toe) Down, 0° Flat and 10°, 20°, 25° Facing (Toe) Up) and postural orientation on the margins of postural stability in quiet standing of young adults. The findings showed that the center of pressure—CoP (displacement, area and length) had least motion at the baseline (0° Flat) platform condition that progressively increased as a function of platform angle in both facing up and down directions. The virtual time to collision (VTC) dynamics revealed that the spatio-temporal margins to the functional stability boundary were progressively smaller and the VTC time series also more regular (SampEn–Sample Entropy) as slope angle increased. Surface slope induces a restricted stability region with lower dimension VTC dynamics that is more constrained when postural orientation is facing down the slope. These findings provide further evidence that VTC acts as a control variable in standing posture ...本研究探讨了支撑面坡度（35°、30°、20°、10°足尖朝下倾斜、0°平坦平台，以及10°、20°、25°足尖朝上倾斜）与身体姿态朝向对青年成年人静立姿态稳定性裕度的影响。研究结果显示，压力中心（center of pressure, CoP）的位移、覆盖面积与轨迹长度在0°平坦平台条件下运动幅度最小，且在足尖朝上和朝下两种倾斜方向中，其运动幅度均随平台倾角增大而逐渐增加。虚拟碰撞时间（virtual time to collision, VTC）的动力学特征表明，随着平台倾角增大，人体到达功能稳定性边界的时空裕度逐渐减小，且VTC时间序列的规则性也更强（样本熵，Sample Entropy，缩写为SampEn）。支撑面坡度会导致人体姿态稳定性区域受限，此时VTC动力学的维度更低；当身体姿态朝向坡下时，这种约束效应更为显著。上述研究结果进一步佐证了VTC可作为站立姿态控制变量的观点……