Biryukova E V, Roschin V Y, Frolov A A, Ioffe M E, Massion J, Dufosse M
Institute of Higher Nervous Activity and Neurophysiology of the Russian Academy of Sciences, Moscow.
Exp Brain Res. 1999 Jan;124(1):107-17. doi: 10.1007/s002210050605.
In this study, the equilibrium-point hypothesis of muscle-torque generation is used to evaluate the changes in central control parameters in the process of postural-maintenance learning. Muscle torque is described by a linear spring equation with modifiable stiffness, viscosity, and equilibrium angle. The stiffness is considered to be the estimation of the central command for antagonist-muscle coactivation and the equilibrium angle to be the estimation of the reciprocal command for a shift of invariant characteristics of the joint. In the experiments, a load applied to the forearm was released. The subjects were instructed to maintain their forearm in the initial horizontal position. Five sessions of approximately twenty trials each were carried out by eight subjects. During two "control" series, the load release was triggered by the experimenter. During three "learning" series, the load supported by one forearm was released by the subject's other hand. The elbow-joint angle, the angular acceleration, and the external load on the postural forearm were recorded. These recordings as well as anthropometric forearm characteristics were used to calculate the elbow-joint torque (which we called "experimental"). Linear regression analysis was performed to evaluate the equilibrium angle, joint stiffness, and viscosity at each trial. The "theoretical" torque was calculated using a linear spring equation with the found parameters. The good agreement observed between experimental and theoretical joint-torque time courses, apart from the very early period following unloading, argues in favor of the idea that the movement was mainly performed under a constant central command presetting the joint stiffness and the equilibrium angle. An overall increase in the stiffness occurred simultaneously with a decrease in the equilibrium angle during the "learning" series in all the subjects. This suggests that subjects learn to compensate for the disturbing effects of unloading by increasing the joint stiffness. The mechanism possibly responsible for the presetting of the central control parameters is discussed.
在本研究中，肌肉扭矩产生的平衡点假说被用于评估姿势维持学习过程中中枢控制参数的变化。肌肉扭矩由一个具有可修改刚度、粘性和平衡角度的线性弹簧方程来描述。刚度被认为是对拮抗肌共同激活的中枢指令的估计，而平衡角度则是对关节不变特征偏移的反向指令的估计。在实验中，施加在前臂上的负荷被释放。受试者被要求将其前臂维持在初始水平位置。八名受试者进行了五个阶段，每个阶段约二十次试验。在两个“对照”系列中，负荷释放由实验者触发。在三个“学习”系列中，由一只前臂支撑的负荷由受试者的另一只手释放。记录了肘关节角度、角加速度以及姿势前臂上的外部负荷。这些记录以及前臂的人体测量特征被用于计算肘关节扭矩（我们称之为“实验性”扭矩）。进行线性回归分析以评估每次试验时的平衡角度、关节刚度和粘性。使用具有所发现参数的线性弹簧方程计算“理论”扭矩。除卸载后的非常早期阶段外，实验性和理论性关节扭矩时间进程之间观察到的良好一致性支持了这样一种观点，即运动主要是在预设关节刚度和平衡角度的恒定中枢指令下进行的。在所有受试者的“学习”系列中，刚度的总体增加与平衡角度的减小同时发生。这表明受试者学会通过增加关节刚度来补偿卸载的干扰效应。讨论了可能负责中枢控制参数预设的机制。
