Importance of body sway velocity information in controlling ankle extensor activities during quiet stance
Importance of body sway velocity information in controlling ankle extensor activities during quiet stance
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DOI：
10.1152/jn.00730.2002
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发表时间：
2003-12-01
影响因子：
2.5
通讯作者：
Nozaki, D
中科院分区：
文献类型：
--
作者：
Masani, K;Popovic, MR;Nozaki, D
在文献中，已经表明，中枢神经系统预期在安静的立场，并不断调节踝伸肌活动，以补偿身体的位置的自发变化的变化。本研究的目的是调查是否速度反馈有助于调制踝伸肌活动的预期方式，促进有效控制安静的立场。通过理论分析和实验研究了速度反馈在多大程度上有助于控制安静姿态。实验是在16名健康受试者中进行的，他们被要求睁着或闭着眼睛安静地站着。在实验过程中，测量前后方向上的压力中心（COP）位移（COPdis）、质心（COM）位移（COMdis）和COM速度（COMvel）。使用整流肌电图（EMG）测量右侧比目鱼肌、内侧腓肠肌和外侧腓肠肌的肌肉活动。使用倒立摆模型进行模拟，该模型描述了安静站立的前后运动学和动力学。在模拟中，假设将使用比例微分（PD）控制器来调节身体的COMdis。在这些仿真中评估了两种不同的PD控制器：1）具有高导数/速度增益（HDG）的控制器和2）具有低导数/速度增益（LDG）的控制器。采用互相关分析方法研究了实验1）COMdis和2）COMvel与EMG的时间序列之间的关系。应用相同的互相关分析来研究在模拟3）COMdis和踝关节扭矩和4）COMvel和踝关节扭矩中获得的时间序列之间的关系。这些分析的结果表明，COMdis与所有三种EMG呈正相关，并且EMG在时间上先于COMdis。这些发现与先前发表的研究结果一致，在这些研究中，外侧腓肠肌在预期身体的COM位置变化时被积极调制。COMvel和所有三种EMG也相关，并且互相关函数（CCF）有两个峰：一个为正，另一个为负。与负峰不同，正峰具有统计学显著性;它们大于负峰;并且它们的时移比负峰的时移短得多。当将这些结果与针对模拟时间序列获得的CCF结果进行比较时，发现HDG控制器的互相关结果与针对实验时间序列的互相关结果紧密匹配。另一方面，LDG控制器的仿真结果与实验结果不一致。这些研究结果表明，在安静的立场，实际的姿势控制系统采用的控制策略，特别是依赖于速度信息，这样的控制器可以调节肌肉活动的预期方式，而不使用前馈机制。
In literature, it has been suggested that the CNS anticipates spontaneous change in body position during quiet stance and continuously modulates ankle extensor muscle activity to compensate for the change. The purpose of this study was to investigate whether velocity feedback contributes by modulating ankle extensor activities in an anticipatory fashion, facilitating effective control of quiet stance. Both theoretical analysis and experiments were carried out to investigate to what extent velocity feedback contributes to controlling quiet stance. The experiments were carried out with 16 healthy subjects who were asked to stand quietly with their eyes open or closed. During the experiments, the center of pressure (COP) displacement (COPdis), the center of mass (COM) displacement (COMdis), and COM velocity (COMvel) in the anteroposterior direction were measured. Rectified electromyograms (EMGs) were used to measure muscle activity in the right soleus muscle, the medial gastrocnemius muscle, and the lateral gastrocnemius muscle. The simulations were performed using an inverted pendulum model that described the anteroposterior kinematics and dynamics of quiet stance. In the simulations, an assumption was made that the COMdis of the body would be regulated using a proportional-derivative (PD) controller. Two different PD controllers were evaluated in these simulations: 1) a controller with the high-derivative/velocity gain (HDG) and 2) a controller with the low-derivative/velocity gain (LDG). Cross-correlation analysis was applied to investigate the relationships between time series obtained in experiments 1) COMdis and EMGs and 2) COMvel and EMGs. Identical cross-correlation analysis was applied to investigate the relationships between time series obtained in simulations 3) COMdis and ankle torque and 4) COMvel and ankle torque. The results of these analyses showed that the COMdis was positively correlated with all three EMGs and that the EMGs temporally preceded the COMdis. These findings agree with the previously published studies in which it was shown that the lateral gastrocnemius muscle is actively modulated in anticipation of the body's COM position change. The COMvel and all three EMGs were also correlated and the cross-correlation function (CCF) had two peaks: one that was positive and another that was negative. The positive peaks were statistically significant, unlike the negative ones; they were larger than the negative peaks; and their time shifts were much shorter compared with the time shifts of the negative peaks. When these results were compared with the CCF results obtained for simulated time series, it was discovered that the cross-correlation results for the HDG controller closely matched cross-correlation results for the experimental time series. On the other hand, the simulation result obtained for LDG controller did not match the experimental results. These findings suggest that the actual postural control system during quiet stance adopts a control strategy that relies notably on velocity information and that such a controller can modulate muscle activity in anticipatory manner without using a feed-forward mechanism.