Engelhart D, Pasma J H, Schouten A C, Aarts R G K M, Meskers C G M, Maier A B, van der Kooij H
Laboratory of Biomechanical Engineering, Institute for Biomedical Technology and Technical Medicine, University of Twente, Enschede, The Netherlands;
Department of Rehabilitation Medicine, Leiden University Medical Centre, Leiden, The Netherlands;
J Neurophysiol. 2016 Mar;115(3):1422-35. doi: 10.1152/jn.00030.2015. Epub 2015 Dec 30.
Standing balance requires multijoint coordination between the ankles and hips. We investigated how humans adapt their multijoint coordination to adjust to various conditions and whether the adaptation differed between healthy young participants and healthy elderly. Balance was disturbed by push/pull rods, applying two continuous and independent force disturbances at the level of the hip and between the shoulder blades. In addition, external force fields were applied, represented by an external stiffness at the hip, either stabilizing or destabilizing the participants' balance. Multivariate closed-loop system-identification techniques were used to describe the neuromuscular control mechanisms by quantifying the corrective joint torques as a response to body sway, represented by frequency response functions (FRFs). Model fits on the FRFs resulted in an estimation of time delays, intrinsic stiffness, reflexive stiffness, and reflexive damping of both the ankle and hip joint. The elderly generated similar corrective joint torques but had reduced body sway compared with the young participants, corresponding to the increased FRF magnitude with age. When a stabilizing or destabilizing external force field was applied at the hip, both young and elderly participants adapted their multijoint coordination by lowering or respectively increasing their neuromuscular control actions around the ankles, expressed in a change of FRF magnitude. However, the elderly adapted less compared with the young participants. Model fits on the FRFs showed that elderly had higher intrinsic and reflexive stiffness of the ankle, together with higher time delays of the hip. Furthermore, the elderly adapted their reflexive stiffness around the ankle joint less compared with young participants. These results imply that elderly were stiffer and were less able to adapt to external force fields.
站立平衡需要脚踝和髋关节之间的多关节协调。我们研究了人类如何调整他们的多关节协调以适应各种条件，以及这种适应在健康年轻参与者和健康老年人之间是否存在差异。通过推/拉杆干扰平衡，在髋关节水平和肩胛骨之间施加两个连续且独立的力干扰。此外，施加外力场，以髋关节处的外部刚度表示，该刚度要么稳定要么破坏参与者的平衡。使用多变量闭环系统识别技术来描述神经肌肉控制机制，通过将纠正性关节扭矩量化为对身体摆动的响应，以频率响应函数（FRF）表示。对FRF进行模型拟合可估计踝关节和髋关节的时间延迟、固有刚度、反射刚度和反射阻尼。与年轻参与者相比，老年人产生了相似的纠正性关节扭矩，但身体摆动减少，这与随着年龄增长FRF幅度增加相对应。当在髋关节处施加稳定或破坏平衡的外力场时，年轻和老年参与者都通过降低或分别增加踝关节周围的神经肌肉控制动作来调整他们的多关节协调，这表现为FRF幅度的变化。然而，与年轻参与者相比，老年人的适应程度较低。对FRF进行模型拟合表明，老年人踝关节的固有和反射刚度较高，同时髋关节的时间延迟也较高。此外，与年轻参与者相比，老年人踝关节周围反射刚度的适应性较低。这些结果表明，老年人更僵硬，并且更难以适应外力场。
