IEEE J Biomed Health Inform. 2021 Sep;25(9):3361-3372. doi: 10.1109/JBHI.2021.3073352. Epub 2021 Sep 3.
Individuals with spinal cord injury suffer from seated instability due to impaired trunk neuromuscular function. Monitoring seated stability toward the development of closed-loop controlled neuroprosthetic technologies could be beneficial for restoring trunk stability during sitting in affected individuals. However, there is a lack of (1) a biomechanical characterization to quantify the relationship between the trunk kinematics and sitting balance; and (2) a validated wearable biomedical device for assessing dynamic sitting posture and fall-risk in real-time. This study aims to: (a) determine the limit of dynamic seated stability as a function of the trunk center of mass (COM) position and velocity relative to the base of support; (b) experimentally validate the predicted limit of stability using traditional motion capture; (c) compare the predicted limit of stability with that predicted in the literature for standing and walking; and (d) validate a wearable device for assessing dynamic seated stability and risk of loss of balance. First, we used a six-segment model of the seated human body for simulation. To obtain the limit of stability, we applied forward dynamics and optimization to obtain the maximum feasible initial velocities of the trunk COM that would bring the trunk COM position to the front-end of the base-of-support for a set of initial COM positions. Second, experimental data were obtained from fifteen able-bodied individuals who maintained sitting balance while base-of-support perturbations were applied with three different amplitudes. A motion capture system and four inertial measurement units (IMUs) were used to estimate the trunk COM motion states (i.e., trunk COM position and velocity). The margin of stability was calculated as the shortest distance of the instantaneous COM motion states to those obtained as the limit of stability in the state-space plane. All experimentally obtained trunk COM motion states fell within the limit of stability. A high correlation and small root-mean-square difference were observed between the estimated trunk COM states obtained by the motion capture system and IMUs. IMU-based wearable technology, along with the predicted limit of dynamic seated stability, can estimate the margin of stability during perturbed sitting. Therefore, it has the potential to monitor the seated stability of wheelchair users affected by trunk instability.
脊髓损伤患者由于躯干神经肌肉功能受损而出现坐姿不稳定。监测坐姿稳定性，以便开发闭环控制神经假体技术，可能有助于恢复受影响个体坐姿时的躯干稳定性。然而，目前缺乏（1）一种生物力学特征来量化躯干运动学与坐姿平衡之间的关系；以及（2）一种经过验证的可穿戴生物医学设备，用于实时评估动态坐姿和跌倒风险。本研究旨在：（a）确定动态坐姿稳定性的极限，作为躯干质心（COM）位置和相对于支撑基础的速度的函数；（b）使用传统运动捕捉实验验证预测的稳定性极限；（c）比较预测的稳定性极限与站立和行走文献中的预测值；以及（d）验证一种用于评估动态坐姿稳定性和平衡丧失风险的可穿戴设备。首先，我们使用了一个六节段的坐姿人体模型进行模拟。为了获得稳定性极限，我们应用了正向动力学和优化，以获得躯干 COM 的最大可行初始速度，该速度将使躯干 COM 位置移动到支撑基础的前端，用于一组初始 COM 位置。其次，从十五名身体健康的个体中获得了实验数据，这些个体在施加支撑基础扰动时保持坐姿平衡，扰动幅度有三种不同。使用运动捕捉系统和四个惯性测量单元（IMU）来估计躯干 COM 的运动状态（即躯干 COM 位置和速度）。稳定性余量被计算为瞬时 COM 运动状态与在状态空间平面中获得的稳定性极限之间的最短距离。所有通过实验获得的躯干 COM 运动状态都在稳定性极限内。运动捕捉系统和 IMU 获得的估计躯干 COM 状态之间观察到高度相关性和小均方根差异。基于 IMU 的可穿戴技术以及预测的动态坐姿稳定性极限，可以估计受躯干不稳定影响的轮椅使用者在受扰坐姿时的稳定性余量。因此，它有潜力监测坐姿不稳定的轮椅使用者的坐姿稳定性。
