Supplementary Material for: Concurrent Validity of Inertially Sensed Measures during Voluntary Body Sway in Silence and while Exposed to a Rhythmic Acoustic Stimulus: A Pilot Study

<b><i>Introduction:</i></b> The effect of rhythmic acoustic stimuli on body sway is of increasing interest due to their positive contribution when training or restoring the control of movement. Inertial sensors show promise as a portable, easier, and more affordable method compared to the force plate “gold standard” concerning the evaluation of postural sway. This study examined the concurrent validity of inertially sensed measures of voluntary body sway against those obtained with a force plate, in silence and while exposed to a rhythmic acoustic stimulus. <b><i>Methods:</i></b> Temporal (sway duration and variability) and spatial (trajectory length, variability, range, velocity, and area) body sway variables were extracted using an inertial sensor (at L5) in synchronization with a force plate, during anteroposterior body sway in silence and while exposed to a rhythmic acoustic stimulus (<i>n</i> = 18 young women; two 70-s trials in each condition). Statistics included bivariate correlations between the inertially sensed and the force plate measures, separately, in silence and with a rhythmic acoustic stimulus, as well as for the effect of the rhythmic acoustic stimulus (percentage difference from silence) (<i>p</i> ≤ 0.05, SPSS v25.0). <b><i>Results:</i></b> The inertially sensed measures demonstrated good-to-excellent concurrent validity for all temporal and almost all spatial variables, both in silence and with rhythmic acoustic stimulus (<i>r</i> &gt; 0.75, <i>p</i> = 0.000), as well as for the rhythmic acoustic-stimulus effect (<i>r</i> &gt; 0.75, <i>p</i> ≤ 0.05). <b><i>Conclusion:</i></b> The inertially sensed measures of the voluntary anteroposterior body sway demonstrated an overall good-to-excellent concurrent validity against those obtained with the force plate “gold standard,” both in the silence and the rhythmic acoustic stimulus conditions, as well as for the rhythmic acoustic-stimulus effect. The findings of this pilot study allow the recommendation of inertial sensing for the evaluation of postural control alterations when exposed to rhythmic acoustic stimuli, a condition of increasing interest due to the positive contribution of such stimuli when training or restoring the control of movement.

<b><i>引言：</i></b> 节奏性声刺激对身体摇晃的影响日益受到关注，因其在运动控制训练或康复中具有积极作用。相较于测力台（force plate）这一"金标准"，惯性传感器（inertial sensor）在姿势摇晃评估方面展现出便携、简便且成本更低的应用前景。本研究针对静息状态下与暴露于节奏性声刺激时的自主身体摇晃，对比分析了惯性传感测量结果与测力台测量结果的同时效度（concurrent validity）。
<b><i>方法：</i></b> 本研究在前后向身体摇晃过程中，分别于静息状态及暴露于节奏性声刺激条件下（<i>n</i> = 18名青年女性；每种条件下开展两次70秒的测试），通过安装于L5椎体的惯性传感器，同步采集了身体摇晃的时域指标（摇晃时长与变异性）及空域指标（轨迹长度、变异性、范围、速度与面积），并与测力台的测量结果进行对照。统计分析分别针对静息状态、节奏性声刺激条件下的惯性传感与测力台测量指标进行双变量相关性分析，同时评估了节奏性声刺激的影响（与静息状态的百分比差异）（<i>p</i> ≤ 0.05，SPSS v25.0）。
<b><i>结果：</i></b> 无论静息状态还是暴露于节奏性声刺激时，惯性传感测量结果在所有时域指标及几乎所有空域指标上均展现出良好至优秀的同时效度（<i>r</i> > 0.75，<i>p</i> = 0.000）；针对节奏性声刺激影响的分析同样获得了显著的良好相关性（<i>r</i> > 0.75，<i>p</i> ≤ 0.05）。
<b><i>结论：</i></b> 针对自主前后向身体摇晃的惯性传感测量结果，相较于测力台这一"金标准"，无论静息状态还是节奏性声刺激条件下，均展现出整体良好至优秀的同时效度，且在节奏性声刺激影响的评估中同样表现优异。本初步研究结果表明，惯性传感可用于评估暴露于节奏性声刺激时的姿势控制变化——这类刺激在运动控制训练与康复中具有积极作用，相关应用场景也日益受到关注。