Table 1_Comparison of marker-based and center-of-pressure-based approaches for calculating the margin of stability.docx

IntroductionThe margin of stability (MoS) is a widely used biomechanical measure of dynamic stability during gait, typically computed as the distance between the extrapolated center of mass (xCoM) and the center of pressure (CoP). According to Hof's model, the CoP-based approach is considered the preferred approach for defining where the xCoM is relative to the BoS and calculating the MoS. However, marker-based approaches often need to be used in research and clinical settings due to practical constraints and the lack of standardization in marker selection introduces variability in MoS estimates. This study aimed to assess the difference between different marker-based approaches and the CoP-based approach.
MethodsUsing an open-access dataset of 30 healthy adults walking at a self-selected speed, MoS was calculated continuously during the stance phase in both the anteroposterior (AP) and mediolateral (ML) directions. Various marker-based approaches were evaluated, including commonly used markers (AP: HEEL, TOE; ML: HEEL, ANKLE, M5, MID) and a novel approach using the most anterior (for AP MoS) or most lateral (for ML MoS) marker in contact with the ground at each time point (AP: MOST ANTERIOR; ML: MOST LATERAL). Differences were quantified using paired t-tests with statistical parametric mapping and root mean square differences (RMSD) relative to the CoP-based approach.
ResultsResults showed that the MOST ANTERIOR approach had the closest agreement with the CoP-based approach for AP MoS (RMSD = 47.04 mm), while the HEEL marker provided the closest agreement with the CoP-based approach for the ML MoS estimates (RMSD = 17.93 mm).
ConclusionThese findings highlight the importance of marker selection in MoS analysis and suggest that specific marker configurations, particularly those grounded in foot-ground contact for the AP-MoS, provide closest estimates relative to the CoP-based approach. This study offers evidence-based recommendations for improving consistency and comparability in future MoS studies using marker-based approaches.

引言
稳定裕度（margin of stability, MoS）是步态动态稳定性的常用生物力学指标，通常计算为外推质心（extrapolated center of mass, xCoM）与压力中心（center of pressure, CoP）之间的距离。根据Hof模型，基于CoP的方法被认为是定义xCoM相对于支撑基底（base of support, BoS）位置并计算MoS的首选方法。然而，受实际条件限制，研究与临床场景中常需采用基于标记点的方法，而标记点选择缺乏标准化会导致MoS估计结果存在变异。本研究旨在评估不同基于标记点的方法与基于CoP的方法之间的差异。

方法
本研究采用包含30名健康成人以自主选择速度行走数据的公开数据集，在站立相期间连续计算前后向（anteroposterior, AP）与内外向（mediolateral, ML）两个方向的MoS。本研究评估了多种基于标记点的方法，包括常用标记点（前后向：HEEL、TOE；内外向：HEEL、ANKLE、M5、MID），以及一种新方法：在每个时间点选取与地面接触的最靠前（用于前后向MoS）或最靠外（用于内外向MoS）的标记点（前后向：MOST ANTERIOR；内外向：MOST LATERAL）。以基于CoP的方法为参照，采用配对t检验结合统计参数映射与均方根差（root mean square differences, RMSD）量化方法间的差异。

结果
结果显示，对于前后向MoS，MOST ANTERIOR方法与基于CoP的方法一致性最高（均方根差=47.04 mm）；而对于内外向MoS估计值，HEEL标记点方法与基于CoP的方法一致性最高（均方根差=17.93 mm）。

结论
本研究结果凸显了标记点选择在MoS分析中的重要性，并表明特定的标记点配置——尤其是基于实时足-地面接触状态的前后向MoS计算方法——相较于基于CoP的方法可获得最精准的估计结果。本研究为未来采用基于标记点方法开展MoS研究时，提升结果一致性与可比性提供了循证建议。