Department of Mechanical Engineering, Brigham Young University, 435 CTB, Provo, UT 84602, United States.
Department of Mechanical Engineering, Brigham Young University, 435 CTB, Provo, UT 84602, United States; Neuroscience Center, Brigham Young University, 435 CTB, Provo, UT 84602, United States.
J Biomech. 2014 Aug 22;47(11):2779-85. doi: 10.1016/j.jbiomech.2014.01.053. Epub 2014 Mar 13.
Human movement generally involves multiple degrees of freedom (DOF) coordinated in a graceful and seemingly effortless manner even though the underlying dynamics are generally complex. Understanding these dynamics is important because it exposes the challenges that the neuromuscular system faces in controlling movement. Despite the importance of wrist and forearm rotations in everyday life, the dynamics of movements involving wrist and forearm rotations are currently unknown. Here we present equations of motion describing the torques required to produce movements combining flexion-extension (FE) and radial-ulnar deviation (RUD) of the wrist and pronation-supination (PS) of the forearm. The total torque is comprised of components required to overcome the effects of inertia, damping, stiffness, and gravity. Using experimentally measured kinematic data and subject-specific impedance parameters (inertia, damping, and stiffness), we evaluated movement torques to test the following hypotheses: the dynamics of wrist and forearm rotations are (1) dominated by stiffness, not inertial or damping effects, (2) significantly coupled through interaction torques due to stiffness and damping (but not inertia), and (3) too complex to be well approximated by a simple, linear model. We found that (1) the dynamics of movements combining the wrist and forearm are similar to wrist rotations in that stiffness dominates over inertial and damping effects (p<0.0001) by approximately an order of magnitude, (2) the DOF of the wrist and forearm are significantly coupled through stiffness, while interactions due to inertia and damping are small, and (3) despite the complexity of the exact equations of motion, the dynamics of wrist and forearm rotations are well approximated by a simple, linear (but still coupled) model (the mean error in predicting torque was less than 1% of the maximum torque). The exact and approximate models are presented for modeling wrist and forearm rotations in future studies.
人体运动通常涉及多个自由度（DOF），这些自由度以优雅且看似毫不费力的方式协调，尽管潜在的动力学通常很复杂。了解这些动力学很重要，因为它揭示了神经系统在控制运动时所面临的挑战。尽管手腕和前臂旋转在日常生活中很重要，但涉及手腕和前臂旋转的运动动力学目前尚不清楚。在这里，我们提出了描述产生结合手腕屈伸（FE）和桡尺偏（RUD）以及前臂旋前-旋后（PS）的运动所需的扭矩的运动方程。总扭矩由克服惯性、阻尼、刚度和重力影响所需的分量组成。使用实验测量的运动学数据和特定于主体的阻抗参数（惯性、阻尼和刚度），我们评估了运动扭矩以检验以下假设：（1）手腕和前臂旋转的动力学主要由刚度决定，而不是惯性或阻尼效应；（2）由于刚度和阻尼（但不是惯性）引起的相互作用扭矩使自由度显著耦合；（3）过于复杂，无法通过简单的线性模型很好地近似。我们发现（1）结合手腕和前臂的运动动力学类似于手腕旋转，即刚度对惯性和阻尼效应的主导作用约为一个数量级（p<0.0001）；（2）手腕和前臂的自由度通过刚度显著耦合，而由于惯性和阻尼引起的相互作用较小；（3）尽管运动方程的精确性很复杂，但手腕和前臂旋转的动力学可以通过简单的线性（但仍耦合）模型很好地近似（预测扭矩的平均误差小于最大扭矩的 1%）。为了在未来的研究中对手腕和前臂旋转进行建模，我们提出了精确和近似模型。
