Mehrez Sadok, Smaoui Hichem
Department of Mechanical Engineering, College of Engineering at Al Kharj, Prince Sattam bin Abdulaziz University, 11942, Saudi Arabia.
LASMAP, Tunisia Polytechnic School, University of Carthage, Tunisia.
Appl Bionics Biomech. 2020 Dec 9;2020:8837147. doi: 10.1155/2020/8837147. eCollection 2020.
Trunk stiffness is an important parameter for trunk stability analysis and needs to be evaluated accurately. Discrepancies regarding the dependence of trunk stiffness on the direction of movement in the sagittal plane suggest inherent sources of error that require explanation. In contrast to the common assumption that the muscle stiffness remains constant prior to the induction of a reflex during position perturbations, it is postulated that muscle-stiffness changes of nonneural origin occur and alter the experimental trunk stiffness, causing it to depend on the sagittal direction. This is confirmed through reinterpretation of existing test data for a healthy subject, numerical simulation, and sensitivity analysis using a biomechanical model. The trunk stiffness is determined through a static approach (in forward and backward directions) and compared with the model stiffness for assumed scenarios involving deactivated muscles. The difference in stiffness between the opposite directions reaches 17.5% without a preload and decreases when a moderate vertical preload is applied. The increased muscle activation induced by preloads or electrical stimuli explains the apparent discrepancies observed in previous studies. The experimental stiffness invariably remains between low and high model-stiffness estimates based on extreme scenarios of the postulated losses of muscle activation, thereby confirming our hypothesis.
躯干刚度是躯干稳定性分析的一个重要参数，需要进行准确评估。关于躯干刚度在矢状面内运动方向依赖性的差异表明存在需要解释的固有误差来源。与在位置扰动期间反射诱发之前肌肉刚度保持恒定的常见假设相反，据推测会发生非神经源性的肌肉刚度变化，并改变实验性躯干刚度，使其依赖于矢状方向。这通过对一名健康受试者现有测试数据的重新解释、数值模拟以及使用生物力学模型的敏感性分析得到了证实。躯干刚度通过静态方法（向前和向后方向）确定，并与涉及肌肉失活的假设场景下的模型刚度进行比较。在没有预载的情况下，相反方向之间的刚度差异达到17.5%，当施加适度的垂直预载时该差异会减小。预载或电刺激引起的肌肉激活增加解释了先前研究中观察到的明显差异。基于假设的肌肉激活丧失的极端情况，实验刚度始终保持在低和高模型刚度估计值之间，从而证实了我们的假设。
