TIME-VARYING MECHANICAL-BEHAVIOR OF MULTIJOINTED ARM IN MAN
TIME-VARYING MECHANICAL-BEHAVIOR OF MULTIJOINTED ARM IN MAN
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DOI：
10.1152/jn.1993.69.5.1443
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发表时间：
1993-05-01
影响因子：
2.5
通讯作者：
BORGHESE, NA
中科院分区：
文献类型：
--
作者：
LACQUANITI, F;CARROZZO, M;BORGHESE, NA
1.本研究的目的是描述随时间变化的多关节肢体的力学参数的变化。我们考虑的参数是刚度系数、粘性系数和惯性系数。连续伪随机扰动施加在手肘关节在捕捉任务。一个修改后的版本的合奏技术用于识别时变参数。然后，手肘关节和腕关节处的扭矩被建模为分别由角刚度矩阵和角粘性矩阵加权的角位置和速度的变化的线性组合。还进行了控制实验，涉及固定维护一个给定的肢体姿势，积极抵抗所施加的扰动。在每个这样的实验中，检查不同的肢体姿势，以研究肢体几何形状对力学参数的依赖性。肢体力学参数的识别技术证明是足够的。手肘关节处施加的输入扰动引起手腕处的角振荡，与手肘处产生的角振荡基本上不相关。手腕处的振荡频率比手肘处高得多，这主要是因为惯性较小。在固定和随时间变化的条件下，该模型占的方差几乎等于80%;在后一种情况下，该值在整个任务中没有显着变化。此外，该模型预测的惯性参数值接近人体测量的测量值，它再现了当球握在手中时肢体惯性的逐步增加。在静止条件下估计的角刚度和粘度的值并没有显着变化与关节角度，在准静态姿势条件下获得的结果与以前的协议。角刚度系数的矩阵是不对称的，表明非自生反射反馈的突出作用，肘部和手腕肌肉的增益不等。一个复杂的时间调制的角刚度和粘度观察在捕捉任务。直接的角刚度系数的变化往往与那些在耦合系数从试验开始到几乎等于30毫秒前的影响时间的协变。然而，在撞击时间前后，有一个完全的分离：直接项达到峰值，而耦合项下降。角粘滞系数的直接项在冲击前也增加，而粘滞系数的耦合项在冲击过程中始终保持接近于零。神经相关的角阻抗的变化被发现，通过考虑在捕捉过程中的净肌电图活动和牵张反射的变化的时间过程。预期的肌肉活动开始前100-200毫秒的影响和相关的定性与预期的变化角刚度。冲击前后刚度和粘度的直接项的峰值可以通过短潜伏期牵张反射反应方向的瞬时逆转来解释。碰撞前后刚度耦合项的减小可以用非均匀拉伸反射增益的瞬时减小来解释.计算了在肢端笛卡尔坐标系中表示刚度和粘性的系数矩阵。从这样的矩阵，对应于由手提供的虚拟垂直位移的阻力矢量的组件被提取。我们发现，手的阻力是准确调制的影响时间。手阻力矢量的大小增加一致的影响之前，虽然有不同的时间过程中的手硬度和粘度。同样在撞击之前，粘性阻力矢量的方向更接近垂直方向，表明在预期扰动的方向上施加了更大的反作用力分量。手粘性矢量的方向与手惯性矢量的方向呈负相关。这一结果表明，存在一个并行的神经控制的不同组成部分的手阻抗，即惯性，刚度和粘度。这种并行控制的前提是准确的内部模型的肢体力学性能的可用性。
1. The aim of this study was to describe the time-varying changes in the mechanical parameters of a multijointed limb. The parameters we considered are the coefficients of stiffness, viscosity, and inertia. Continuous pseudorandom perturbations were applied at the elbow joint during a catching task. A modified version of an ensemble technique was used for the identification of time-varying parameters. Torques at the elbow and wrist joints were then modeled with a linear combination of the changes in angular position and velocity weighed by the matrix of angular stiffness and the matrix of angular viscosity, respectively. Control experiments were also performed that involved the stationary maintenance of a given limb posture by resisting actively the applied perturbations. Different limb postures were examined in each such experiment to investigate the dependence of the mechanical parameters on limb geometry.2. The technique for the identification of limb mechanical parameters proved adequate. The input perturbations applied at the elbow joint elicited angular oscillations at the wrist essentially uncorrelated with those produced at the elbow. The frequency of oscillation is much higher at the wrist than at the elbow, mainly because of the smaller inertia. The variance accounted for by the model was almost-equal-to 80% under both stationary and time-varying conditions; in the latter case the value did not vary significantly throughout the task. In addition, the model predicted values of the inertial parameters that were close to the anthropometric measures, and it reproduced the stepwise increase in limb inertia that occurs at the time the ball is held in the hand.3. The values of angular stiffness and viscosity estimated under stationary conditions did not vary significantly with joint angle, in agreement with previous results obtained under quasistatic postural conditions. The matrix of the coefficients of angular stiffness was not symmetrical, indicating a prominent role for nonautogenic reflex feedbacks with unequal gains for elbow and wrist muscles.4. A complex temporal modulation of angular stiffness and viscosity was observed during the catching task. The changes in the direct coefficients of angular stiffness tended to covary with those in the coupling coefficients from trial start up to almost-equal-to 30 ms before impact time. Around impact time, however, there was a complete dissociation: the direct terms peaked, whereas the coupling terms dropped. The direct terms of angular viscosity also increased before impact, whereas the viscosity coupling terms remained close to zero throughout.5. Neural correlates of the changes in angular impedance were found by considering the time course of the changes in net electromyographic activity and stretch reflexes during catching. Anticipatory muscle activity started 100-200 ms before impact and correlated qualitatively with anticipatory changes in angular stiffness. The peaks of the direct terms of stiffness and viscosity around impact could be accounted by the transient reversal of the direction of short-latency stretch reflex responses. The decrease of the coupling terms of stiffness around impact could be explained by a transient decrease of the gain of heteronymous stretch reflexes.6. The matrices of the coefficients expressing stiffness and viscosity in the Cartesian coordinates of the limb endpoint were also computed. From such matrices, the components corresponding to the vectors of resistance offered by the hand to a virtual vertical displacement were extracted. We found that the hand resistance is accurately modulated relative to the impact time. The magnitude of hand resistance vectors increased consistently before impact, although with a different time course for hand stiffness and viscosity. Also before impact, the direction of viscous resistance vectors rotated closer to the vertical, indicating that a larger component of reactive force is exerted in the direction of the expected perturbation.7. The orientation of the vectors of hand viscosity was variably correlated with the orientation of the vectors of hand inertia during catching. This result suggests the existence of a parallel neural control of different components of hand impedance, that is inertia, stiffness, and viscosity. This parallel control is predicated on the availability of accurate internal models of the limb mechanical properties.