OBJECTIVE Are people with a characteristically large physiological sway rendered particularly unstable when standing on a moving surface? Is postural sway in standing individuals idiosyncratic? In this study, we examine postural sway in individuals standing normally, and when subtle continuous sinusoidal disturbances are applied to their support platform. We calculate consistency between conditions to verify if sway can be considered characteristic of each individual. We also correlate two different aspects of participants’ responses to disturbance; their sway velocity and their regulation of body orientation. METHODS Nineteen healthy adults (age 29.2 ± 3.2 years) stood freely on footplates coaxially aligned with their ankles and attached to a motorized platform. They had their eyes closed, and hips and knees locked with a light wooden board attached to their body. Participants either stood quietly on a fixed platform or on a slowly tilting platform (0.1 Hz sinusoid; 0.2 & 0.4 deg). Postural sway size was separated into two entities: (1) the spontaneous sway velocity component (natural random relatively rapid postural adjustments, RMS body angular velocity), and (2) the evoked tilt gain component (much slower 0.1 Hz synchronous tilt induced by the movement of the platform, measured as p-p gain, ratio of body angle to applied footplate rotation). RESULTS There was no correlation between the velocity of an individual’s sway and their evoked tilt gain (r=0.34, p=0.15 and r=0.30, p=0.22). However, when considered separately, each of the two measurements showed fair to good absolute agreement within conditions. Spontaneous sway velocity consistently increased as participants were subjected to increasing disturbance. Participants who swayed more (or less) did so across all conditions (ICC(3,k) = 0.95). Evoked tilt gain also showed consistency between conditions (ICC(3,k) = 0.79), but decreased from least to most disturbed conditions. CONCLUSION The two measurements remain consistent between conditions. Consistency between conditions of two very distinct unrelated measurements reflects the idiosyncratic nature of postural sway. However, sway velocity and tilt gain are not related, which supports the idea that the short-term regulation of stability and the longer-term regulation of orientation are controlled by different processes.

中文翻译：

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正常和扰动站立姿势摇摆的特殊特征

目标 具有较大生理摇摆特征的人站在移动的表面上时是否会变得特别不稳定？站立的人的姿势摇摆是特异的吗？在这项研究中，我们检查了正常站立的个体的姿势摇摆，以及当微妙的连续正弦波干扰应用于他们的支撑平台时。我们计算条件之间的一致性，以验证是否可以将摇摆视为每个人的特征。我们还将参与者对干扰反应的两个不同方面关联起来；他们的摇摆速度和他们对身体方向的调节。方法 19 名健康成人（年龄 29.2 ± 3.2 岁）自由站立在与脚踝同轴并附在电动平台上的踏板上。他们闭着眼睛，臀部和膝盖用一块轻木板固定在他们的身体上。参与者要么安静地站在固定平台上，要么站在缓慢倾斜的平台上（0.1 Hz 正弦曲线；0.2 和 0.4 度）。姿势摇摆大小分为两个实体：（1）自发摇摆速度分量（自然随机相对快速的姿势调整，RMS 身体角速度），和（2）诱发倾斜增益分量（慢得多的 0.1 Hz 同步倾斜由平台的运动，测量为 pp 增益，身体角度与应用踏板旋转的比率）。结果 个人摇摆的速度与其诱发的倾斜增益之间没有相关性（r=0.34，p=0.15 和 r=0.30，p=0.22）。然而，当单独考虑时，这两个测量值中的每一个都显示出在条件下相当到良好的绝对一致性。随着参与者受到越来越多的干扰，自发摇摆速度持续增加。摇摆更多（或更少）的参与者在所有条件下都这样做（ICC（3，k）= 0.95）。诱发倾斜增益也显示条件之间的一致性 (ICC(3,k) = 0.79)，但从最少到最受干扰的条件下降。结论 这两个测量值在条件之间保持一致。两个非常不同的不相关测量条件之间的一致性反映了姿势摇摆的特殊性质。然而，摇摆速度和倾斜增益无关，这支持了稳定性的短期调节和方向的长期调节受不同过程控制的观点。摇摆更多（或更少）的参与者在所有条件下都这样做（ICC（3，k）= 0.95）。诱发倾斜增益也显示条件之间的一致性 (ICC(3,k) = 0.79)，但从最少到最受干扰的条件下降。结论 这两个测量值在条件之间保持一致。两个非常不同的不相关测量条件之间的一致性反映了姿势摇摆的特殊性质。然而，摇摆速度和倾斜增益无关，这支持了稳定性的短期调节和方向的长期调节受不同过程控制的观点。摇摆更多（或更少）的参与者在所有条件下都这样做（ICC（3，k）= 0.95）。诱发倾斜增益也显示条件之间的一致性 (ICC(3,k) = 0.79)，但从最少到最受干扰的条件下降。结论 这两个测量值在条件之间保持一致。两个非常不同的不相关测量条件之间的一致性反映了姿势摇摆的特殊性质。然而，摇摆速度和倾斜增益无关，这支持了稳定性的短期调节和方向的长期调节受不同过程控制的观点。结论 这两个测量值在条件之间保持一致。两个非常不同的不相关测量条件之间的一致性反映了姿势摇摆的特殊性质。然而，摇摆速度和倾斜增益无关，这支持了稳定性的短期调节和方向的长期调节受不同过程控制的观点。结论 这两个测量值在条件之间保持一致。两个非常不同的不相关测量条件之间的一致性反映了姿势摇摆的特殊性质。然而，摇摆速度和倾斜增益无关，这支持了稳定性的短期调节和方向的长期调节受不同过程控制的观点。