School of Kinesiology, University of Michigan, Ann Arbor, MI, USA.
School of Kinesiology, University of Michigan, Ann Arbor, MI, USA; Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA.
J Biomech. 2019 Mar 6;85:67-73. doi: 10.1016/j.jbiomech.2019.01.005. Epub 2019 Jan 11.
Assessments of shoulder dynamics (e.g. the inertial, viscous, and stiffness properties of the joint) can provide important insights into the stability of the joint at rest and during volitional contraction. The purpose of this study was to investigate how arm posture influences shoulder dynamics while generating pushing or pulling torques in the horizontal plane. Sixteen healthy participants were examined in seven postures encompassing a large workspace of the shoulder. At each posture, the participant's shoulder was rapidly perturbed while measuring the resultant change in shoulder torque about the glenohumeral axis. Participants were examined both at rest and while producing horizontal flexion and extension torques scaled to 15% of a maximum voluntary contraction. Shoulder stiffness, viscosity, and damping ratio were estimated using impedance-based matching, and changes in these outcome measures with torque level, elevation angle, and plane of elevation angle were explored with a linear mixed effects model. Shoulder stiffness was found to decrease with increasing elevation angles (p < 0.001) without subsequent changes in viscosity, leading to a greater damping ratios at higher elevation angles (p < 0.001). Shoulder stiffness, viscosity, and damping ratio (all p < 0.05) were all found to significantly increase as the plane of elevation of the arm was increased. The relationship between the viscosity, stiffness and the damping ratio of the shoulder is one that the central nervous system must regulate in order to maintain stability, protect against injury, and control the shoulder joint as the inertial and muscle contributions change across different arm postures.
评估肩部动力学（例如关节的惯性、粘性和刚度特性）可以深入了解关节在休息和自主收缩时的稳定性。本研究旨在探讨在产生水平平面推或拉力时，手臂姿势如何影响肩部动力学。16 名健康参与者在涵盖肩部大工作空间的七种姿势中接受检查。在每种姿势下，当测量盂肱关节轴上的肩部扭矩的变化时，会快速干扰参与者的肩部。参与者在休息时和产生 15%最大自主收缩的水平屈伸扭矩时都接受了检查。使用基于阻抗的匹配来估计肩部刚度、粘性和阻尼比，并使用线性混合效应模型探讨这些结果指标随扭矩水平、仰角和仰角平面的变化。发现肩部刚度随仰角的增加而降低（p<0.001），而粘性没有随后的变化，导致在较高仰角下具有更大的阻尼比（p<0.001）。发现肩部刚度、粘性和阻尼比（均 p<0.05）都随着手臂仰角平面的增加而显著增加。为了保持稳定性、防止受伤以及随着不同手臂姿势下的惯性和肌肉贡献的变化来控制肩部关节，中枢神经系统必须调节肩部的粘性、刚度和阻尼比之间的关系。
