Worthen-Chaudhari Lise C, Monfort Scott M, Bland Courtney, Pan Xueliang, Chaudhari Ajit M W
Department of Physical Medicine & Rehabilitation, The Ohio State University, Columbus, OH, USA; Neurological Institute, The Ohio State University, Columbus, OH, USA.
Department of Mechanical & Industrial Engineering, Montana State University, Bozeman, MT, USA.
Gait Posture. 2018 Jul;64:141-146. doi: 10.1016/j.gaitpost.2018.05.031. Epub 2018 Jun 2.
To longitudinally assess individuals using quantified measures, we must characterize within-subject variability (WSV) of the measures.
What is the natural within-subject variability (WSV) that can be expected in postural control over 3+ days?
Thirteen individuals without orthopedic or neurologic impairment (mean(SD) = 55 (9) years; 76 (18) kg; 11 females/2 males) were recruited from a community workplace and consented to participate. Participants stood quietly with eyes closed (QEC) on a force platform (5 x 1 min x 6 days) in two stances: comfortable and narrow. We recorded center of pressure (COP) and calculated COP-based balance parameters. To analyze variance components, we applied a linear mixed model for repeated measures, calculating within-subject standard deviation (SDws) from the pooled variance not attributable to between-subject variability. To estimate WSV, we scaled SDws by a confidence interval (CI) factor (e.g. WSV at the 95%CI = WSV = SDws * 1.96) and report WSV for a range of conditions previously reported in the literature and the following measures previously found sensitive to or predictive of health: (primary) WSV of root-mean square amplitude of medial-lateral COP during QEC (RMSml); (secondary) WSV of COP ellipse area (COPa); (secondary) WSV of mean medial-lateral COP velocity (COPvml) during QEC.
WSV was estimated at RMSml = 0.8 mm, COPa = 99mm, and COPvml = 1.1 mm/s among healthy, middle-aged participants standing comfortably for one recommended data duration (4 × 30 s trials). A look up table provides values for alternate protocols that have been suggested in the literature and might prove relevant for clinical translation.
This work advances longitudinal assessment of individuals using quantified measures of postural control. Results enable practitioners/researchers to assess an individual's progress, maintenance, or decline relative to WSV at a defined CI level.
为了使用量化指标对个体进行纵向评估，我们必须描述这些指标的个体内变异性（WSV）。
在超过3天的姿势控制中，预期的自然个体内变异性（WSV）是多少？
从一个社区工作场所招募了13名无骨科或神经损伤的个体（平均（标准差）=55（9）岁；76（18）千克；11名女性/2名男性），他们同意参与研究。参与者在测力平台上闭眼安静站立（QEC）（5×1分钟×6天），采用两种姿势：舒适姿势和窄支撑姿势。我们记录了压力中心（COP）并计算了基于COP的平衡参数。为了分析方差成分，我们应用了重复测量的线性混合模型，从未归因于个体间变异性的合并方差中计算个体内标准差（SDws）。为了估计WSV，我们通过一个置信区间（CI）因子对SDws进行缩放（例如，95%CI时的WSV = WSV = SDws * 1.96），并报告文献中先前报道的一系列条件下的WSV以及先前发现对健康敏感或具有预测性的以下指标：（主要）闭眼安静站立时内侧-外侧COP均方根振幅（RMSml）的WSV；（次要）COP椭圆面积（COPa）的WSV；（次要）闭眼安静站立时平均内侧-外侧COP速度（COPvml）的WSV。
在健康的中年参与者舒适站立一个推荐数据时长（4×30秒试验）的情况下，估计WSV为：RMSml = 0.8毫米，COPa = 99毫米，COPvml = 1.1毫米/秒。一个查找表提供了文献中建议的替代方案的值，这些值可能对临床转化具有相关性。
这项工作推进了使用姿势控制量化指标对个体的纵向评估。结果使从业者/研究人员能够在定义的CI水平上评估个体相对于WSV的进展、维持或下降情况。
