Zonnino Andrea, Sergi Fabrizio
Human Robotics Laboratory,Department of Biomedical Engineering,University of Delaware,Newark, DE 19713e-mail:
J Biomech Eng. 2019 Apr 1;141(4). doi: 10.1115/1.4042684.
The control of joint stiffness is a fundamental mechanism used to control human movements. While many studies have observed how stiffness is modulated for tasks involving shoulder and elbow motion, a limited amount of knowledge is available for wrist movements, though the wrist plays a crucial role in manipulation. We have developed a computational framework based on a realistic musculoskeletal model, which allows one to calculate the passive and active components of the wrist joint stiffness. We first used the framework to validate the musculoskeletal model against experimental measurements of the wrist joint stiffness, and then to study the contribution of different muscle groups to the passive joint stiffness. We finally used the framework to study the effect of muscle cocontraction on the active joint stiffness. The results show that thumb and finger muscles play a crucial role in determining the passive wrist joint stiffness: in the neutral posture, the direction of maximum stiffness aligns with the experimental measurements, and the magnitude increases by 113% when they are included. Moreover, the analysis of the controllability of joint stiffness showed that muscle cocontraction positively correlates with the stiffness magnitude and negatively correlates with the variability of the stiffness orientation (p < 0.01 in both cases). Finally, an exhaustive search showed that with appropriate selection of a muscle activation strategy, the joint stiffness orientation can be arbitrarily modulated. This observation suggests the absence of biomechanical constraints on the controllability of the orientation of the wrist joint stiffness.
关节刚度的控制是用于控制人体运动的一种基本机制。虽然许多研究已经观察到在涉及肩部和肘部运动的任务中刚度是如何调节的，但对于腕部运动的相关知识却很有限，尽管腕部在操作中起着关键作用。我们基于一个逼真的肌肉骨骼模型开发了一个计算框架，该框架能够计算腕关节刚度的被动和主动成分。我们首先使用该框架根据腕关节刚度的实验测量结果来验证肌肉骨骼模型，然后研究不同肌肉群对被动关节刚度的贡献。我们最后使用该框架来研究肌肉协同收缩对主动关节刚度的影响。结果表明，拇指和手指肌肉在决定被动腕关节刚度方面起着关键作用：在中立姿势下，最大刚度方向与实验测量结果一致，当包含这些肌肉时，刚度大小增加了113%。此外，对关节刚度可控性的分析表明，肌肉协同收缩与刚度大小呈正相关，与刚度方向的变异性呈负相关（两种情况均p < 0.01）。最后，详尽的搜索表明，通过适当选择肌肉激活策略，可以任意调节关节刚度方向。这一观察结果表明，在腕关节刚度方向的可控性方面不存在生物力学限制。
