Neural Control of Movement Laboratory, School of Medicine, Faculty of Science, Medicine & Health, University of Wollongong, Wollongong, New South Wales, Australia.
Department of Physical Therapy, College of Health Professions, Virginia Commonwealth University, Richmond, Virginia.
J Neurophysiol. 2021 Nov 1;126(5):1465-1477. doi: 10.1152/jn.00093.2021. Epub 2021 Sep 29.
Postural muscle activity precedes voluntary movements of the upper limbs. The traditional view of this activity is that it anticipates perturbations to balance caused by the movement of a limb. However, findings from reach-based paradigms have shown that postural adjustments can initiate center of mass displacement for mobility rather than minimize its displacement for stability. Within this context, altering reaching distance beyond the base of support would place increasing constraints on equilibrium during stance. If the underlying composition of anticipatory postural activity is linked to stability, coordination between muscles (i.e., motor modules) may evolve differently as equilibrium constraints increase. We analyzed the composition of motor modules in functional trunk muscles as participants performed multidirectional reaching movements to targets within and beyond the arm's length. Bilateral trunk and reaching arm muscle activity were recorded. Despite different trunk requirements necessary for successful movement, and the changing biomechanical (i.e., postural) constraints that accompany alterations in reach distance, nonnegative matrix factorization identified functional motor modules derived from preparatory trunk muscle activity that shared common features. Relative similarity in modular weightings (i.e., composition) and spatial activation profiles that reflect movement goals across tasks necessitating differing levels of trunk involvement provides evidence that preparatory postural adjustments are linked to the same task priorities (i.e., movement generation rather than stability). Reaching within and beyond arm's length places different task constraints upon the required trunk motion necessary for successful movement execution. The identification of constant modular features, including functional muscle weightings and spatial tuning, lend support to the notion that preparatory postural adjustments of the trunk are tied to the same task priorities driving mobility, regardless of the future postural constraints.
姿势肌肉活动先于上肢的随意运动。对这种活动的传统观点是，它预测了肢体运动引起的平衡扰动。然而，基于伸手的范式的研究结果表明，姿势调整可以为移动性启动质心位移，而不是为稳定性最小化其位移。在这种情况下，超出支撑基础的伸手距离会增加站立时平衡的约束。如果预期性姿势活动的基本组成与稳定性有关，那么随着平衡约束的增加，肌肉（即运动模块）之间的协调可能会以不同的方式演变。我们分析了参与者在手臂长度内和超出手臂长度的目标进行多方向伸手运动时，功能型躯干肌肉中运动模块的组成。记录了双侧躯干和伸手臂肌肉的活动。尽管成功运动需要不同的躯干要求，并且随着伸手距离的改变，生物力学（即姿势）约束也在不断变化，但非负矩阵分解确定了源自预备躯干肌肉活动的功能运动模块，这些模块具有共同的特征。在需要不同程度躯干参与的任务中，反映运动目标的模块权重（即组成）和空间激活谱的相对相似性表明，预备性姿势调整与相同的任务优先级（即运动生成而不是稳定性）相关。在手臂长度内和超出手臂长度的伸手会对成功运动执行所需的躯干运动施加不同的任务约束。确定恒定的模块特征，包括功能肌肉权重和空间调谐，支持这样的观点，即躯干的预备性姿势调整与驱动移动性的相同任务优先级有关，而与未来的姿势约束无关。
