Inkol Keaton A, Huntley Andrew H, Vallis Lori Ann
Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Canada.
Toronto Rehabilitation Institute, University Health Network, Toronto, Canada.
Gait Posture. 2018 May;62:434-439. doi: 10.1016/j.gaitpost.2018.03.050. Epub 2018 Mar 30.
Maintaining the centre of mass (CoM) of the body within the base of support is a critical component of upright balance; the ability to accurately quantify balance recovery mechanisms is critical for many research teams.
The purpose of this study was to investigate how exclusion of specific body segments in an anthropometric CoM model influenced a dynamic measure of postural stability, the margin of stability (MoS), following a support-surface perturbation.
Healthy young adults (n = 10) were instrumented with kinematic markers and a safety harness. Sixteen support-surface translations, scaled to ensure responses did not involve a change in base of support, were then issued (backwards, forwards, left, or right). Whole-body CoM was estimated using four variations of a 13-segment anthropometric model: i) the full-model (WFM), and three simplified models, ii) excluding upper limbs (NAr); iii) excluding upper and lower limbs (HTP); iv) pelvis CoM (CoMp). The CoM calculated for each variant was then used to estimate extrapolated CoM (xCoM) position and the resulting MoS within the plane of postural disturbance.
Comparisons of simplified models to the full model revealed significant differences (p < 0.05) in MoS for all models in each perturbation condition; however, the largest differences were following sagittal plane based perturbations. Poor estimates of WFM MoS were most evident for HTP and CoMp models; these were associated with the greatest values of RMS/maximum error, poorest correlations, etc. The simplified models provided low-error approximates for frontal plane perturbations.
Findings suggest that simplified calculations of CoM can be used by researchers without reducing MoS measurement accuracy; however, the degree of simplification should be context-dependent. For example, CoMp models may be appropriate for questions pertaining to frontal plane MoS; sagittal plane MoS necessitates inclusion of lower limb and HTP segments to prevent underestimation of postural stability.
保持身体重心（CoM）处于支撑面内是直立平衡的关键组成部分；对于许多研究团队而言，准确量化平衡恢复机制的能力至关重要。
本研究的目的是调查在人体测量学CoM模型中排除特定身体节段如何影响支撑面扰动后姿势稳定性的动态测量指标——稳定裕度（MoS）。
对10名健康年轻成年人使用运动学标记物和安全带进行测量。随后进行16次支撑面平移（向后、向前、向左或向右），并进行缩放以确保反应不涉及支撑面的变化。使用一个13节段人体测量模型的四种变体估计全身CoM：i）全模型（WFM），以及三种简化模型，ii）排除上肢（NAr）；iii）排除上肢和下肢（HTP）；iv）骨盆CoM（CoMp）。然后，将为每个变体计算的CoM用于估计外推CoM（xCoM）位置以及姿势扰动平面内的所得MoS。
简化模型与全模型的比较显示，在每种扰动条件下，所有模型的MoS均存在显著差异（p < 0.05）；然而，最大差异出现在基于矢状面的扰动之后。HTP和CoMp模型对WFM MoS的估计最差；这些与均方根/最大误差的最大值、最差的相关性等相关。简化模型为额面扰动提供了低误差近似值。
研究结果表明，研究人员可以使用CoM的简化计算方法，而不会降低MoS测量的准确性；然而，简化程度应视具体情况而定。例如，CoMp模型可能适用于与额面MoS相关的问题；矢状面MoS需要纳入下肢和HTP节段，以防止低估姿势稳定性。
