Muscle synergies during voluntary body sway: combining across-trials and within-a-trial analyses
Muscle synergies during voluntary body sway: combining across-trials and within-a-trial analyses
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DOI：
10.1007/s00221-006-0513-8
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发表时间：
2006-10-01
影响因子：
2
通讯作者：
Latash, Mark L.
中科院分区：
文献类型：
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作者：
Wang, Yun;Asaka, Tadayoshi;Latash, Mark L.
我们研究了在需要快速转移压力中心（COP）的自愿摇摆任务中肌肉活动的共变变化。我们假设，多肌肉协同作用（定义为元素变量、肌肉模式的任务特异性协变）在自主COP移位之前稳定了COP在前后方向的位置，并且在移位过程中协同作用会减弱。站立的受试者执行了两项任务，一项是在1 Hz频率下，在自愿COP位移最大幅度的80%范围内进行周期性COP位移，另一项是在相同的名义幅度上进行单向快速COP位移。循环摇摆任务用于定义肌肉模式（m -模式，腿部和躯干肌肉群，在一组肌肉激活水平平行缩放）以及m -模式大小的微小变化之间的关系[在主成分分析（PCA）中，m -模式大小相当于PC分数]和COP变化。采用了一种新颖的方法，将PCA应用于一个试验内和跨试验测量的肌肉综合活动指数。单向摇摆任务采用自定节奏（SP）方式，在典型的简单反应时间（RT）指令下进行。在这些任务的试验中也定义了m模式；它们在不同的任务中都是相似的。sp -摇摆和rt -摇摆任务的肌肉活动综合指标转化为m模式。m模式空间的方差被划分为两个分量，一个不影响COP位移的平均值（V (UCM)），另一个影响COP位移的平均值（V (ORT)）。计算对应于V （UCM）和V （ORT）之间归一化差的指数（Delta V）。在稳态状态下，Delta V为正，对应于大多数m -模态方差位于子空间中，对应于跨试验的稳定COP位置。正δ V值被解释为反映了稳定COP位置的多m模式协同作用。在SP试验中δ V的幅度大于RT试验。在自愿COP轮班期间，δ V级降至零甚至变为负值。我们得出结论，m模式协同作用在安静站立期间稳定COP位置，而这些协同作用在快速自愿COP转换期间减弱或消失。在RT条件下，COP稳定协同效应较弱，可能是为了促进COP快速转移而没有时间准备。建议的m模式识别方法可能潜在地应用于分析姿势控制受损的人，如老年人、非典型发育者或受伤后康复过程中的姿势协同作用。
We investigated co-varied changes in muscle activity during voluntary sway tasks that required a quick shift of the center of pressure (COP). We hypothesized that multi-muscle synergies (defined as task-specific covariation of elemental variables, muscle modes) stabilize a COP location in the anterior-posterior direction prior to a voluntary COP shift and that during the shift the synergies would weaken. Standing subjects performed two tasks, a cyclic COP shift over a range corresponding to 80% of the maximal amplitude of voluntary COP shift at 1 Hz and a unidirectional quick COP shift over the same nominal amplitude. The cyclic sway task was used to define muscle modes (M-modes, leg and trunk muscle groups with parallel scaling of muscle activation level within a group) and the relations between small changes in the magnitudes of M-modes [in the principal component analysis (PCA), the M-mode magnitudes are equivalent to PC scores] and COP shifts. A novel approach was used involving PCA applied to indices of muscle integrated activity measured both within a trial and across trials. The unidirectional sway task was performed in a self-paced (SP) manner and under a typical simple reaction time (RT) instruction. M-modes were also defined along trials at those tasks; they have been shown to be similar across tasks. Integrated indices of muscle activity in the SP-sway and RT-sway tasks were transformed into the M-modes. Variance in the M-mode space was partitioned into two components, one that did not affect the average value of COP shift (V (UCM)) and the other that did (V (ORT)). An index (Delta V) corresponding to the normalized difference between V (UCM) and V (ORT) was computed. During steady-state posture, Delta V was positive corresponding to most M-mode variance lying in a sub-space corresponding to a stable COP location across trials. Positive Delta V values have been interpreted as reflecting a multi-M-mode synergy stabilizing the COP location. The magnitude of Delta V was larger in SP trials than in RT trials. During voluntary COP shifts, the Delta V magnitude dropped to zero or even became negative. We conclude that M-mode synergies stabilize COP location during quiet standing, while these synergies weaken or disappear during fast voluntary COP shifts. Under RT conditions, the COP stabilizing synergies were weaker supposedly to facilitate a quick COP shift without time for preparation. The suggested method of M-mode identification may potentially be applied to analysis of postural synergies in persons with impaired postural control such as elderly persons, persons with atypical development, or in the course of rehabilitation after an injury.