Stollenmaier Katrin, Ilg Winfried, Haeufle Daniel F B
Department of Cognitive Neurology, Hertie Institute for Clinical Brain Research and Werner Reichardt Centre for Integrative Neuroscience, University of Tübingen, Tübingen, Germany.
Front Bioeng Biotechnol. 2020 Apr 21;8:308. doi: 10.3389/fbioe.2020.00308. eCollection 2020.
Human movement is generated by a dynamic interplay between the nervous system, the biomechanical structures, and the environment. To investigate this interaction, we propose a neuro-musculoskeletal model of human goal-directed arm movements. Using this model, we simulated static perturbations of the inertia and damping properties of the arm, as well as dynamic torque perturbations for one-degree-of freedom movements around the elbow joint. The controller consists of a feed-forward motor command and feedback based on muscle fiber length and contraction velocity representing short-latency (25 ms) or long-latency (50 ms) stretch reflexes as the first neuronal responses elicited by an external perturbation. To determine the open-loop control signal, we parameterized the control signal resulting in a piecewise constant stimulation over time for each muscle. Interestingly, such an intermittent open-loop signal results in a smooth movement that is close to experimental observations. So, our model can generate the unperturbed point-to-point movement solely by the feed-forward command. The feedback only contributed to the stimulation in perturbed movements. We found that the relative contribution of this feedback is small compared to the feed-forward control and that the characteristics of the musculoskeletal system create an immediate and beneficial reaction to the investigated perturbations. The novelty of these findings is (1) the reproduction of static as well as dynamic perturbation experiments in one neuro-musculoskeletal model with only one set of basic parameters. This allows to investigate the model's neuro-muscular response to the perturbations that-at least to some degree-represent stereotypical interactions with the environment; (2) the demonstration that in feed-forward driven movements the muscle characteristics generate a mechanical response with zero-time delay which helps to compensate for the perturbations; (3) that this model provides enough biomechanical detail to allow for the prediction of internal forces, including joint loads and muscle-bone contact forces which are relevant in ergonomics and for the development of assistive devices but cannot be observed in experiments.
人体运动是由神经系统、生物力学结构和环境之间的动态相互作用产生的。为了研究这种相互作用，我们提出了一种用于人体目标导向手臂运动的神经肌肉骨骼模型。利用该模型，我们模拟了手臂惯性和阻尼特性的静态扰动，以及围绕肘关节的单自由度运动的动态扭矩扰动。控制器由前馈运动指令和基于肌肉纤维长度和收缩速度的反馈组成，分别代表短潜伏期（25毫秒）或长潜伏期（50毫秒）的牵张反射，这是外部扰动引发的首批神经元反应。为了确定开环控制信号，我们对控制信号进行参数化，使得每个肌肉随时间产生分段恒定刺激。有趣的是，这样一个间歇性的开环信号会产生一个接近实验观察结果的平滑运动。因此，我们的模型仅通过前馈指令就能产生无扰动的点对点运动。反馈仅在受扰动运动中对刺激有贡献。我们发现，与前馈控制相比，这种反馈的相对贡献较小，并且肌肉骨骼系统的特性会对所研究的扰动产生即时且有益的反应。这些发现的新颖之处在于：（1）在一个仅具有一组基本参数的神经肌肉骨骼模型中再现了静态和动态扰动实验。这使得能够研究该模型对扰动的神经肌肉反应，这些扰动至少在一定程度上代表了与环境的典型相互作用；（2）证明在前馈驱动的运动中，肌肉特性会产生零时间延迟的机械反应，这有助于补偿扰动；（3）该模型提供了足够的生物力学细节，以预测包括关节负荷和肌肉 - 骨接触力在内的内力，这些内力在人体工程学和辅助设备开发中是相关的，但在实验中无法观察到。
