Hogan N, Bizzi E, Mussa-Ivaldi F A, Flash T
Exerc Sport Sci Rev. 1987;15:153-90.
Much can be learned about the central nervous system from a study of motor coordination, but its true richness and complexity become evident only in a multiarticular system. Despite the intrinsic complexity of multiarticular actions, they offer an unparalleled opportunity to learn about the central nervous system in a quantitative and experimentally testable way. For example, the observation that unconstrained, unperturbed arm movements are coordinated in terms of hand motion shows that motor control is organized in a hierarchy of increasing levels of abstraction. These arm motions are organized as though a disembodied hand could be moved in space; the details of how this is to be achieved must then be supplied by a different level in the hierarchy. The essence of human behavior is its adaptability. Just as the true complexity of coordination is evident only in multiarticular actions, the sophistication and subtlety of adaptive behavior are evident only in dynamic, interactive tasks. A study of movement alone is not sufficient to understand this behavior. The dynamic response of the limbs becomes the overriding concern and must be controlled by the central nervous system. The dynamic response of a limb is usually associated with its posture, rather than its movement, but in a functional task such as the use of a tool, the postural dynamics are an integral part of the action. This perspective on motor behavior leads to some useful insights. Coordination is not a problem for movement alone; in a multiarticular system, even posture requires coordination and control. Muscles do not merely act reciprocally to generate forces about the joints; the net mechanical impedance of the limb may be controlled by synergistic activation of all muscles, including antagonists. Controlling dynamic behavior is a far more demanding task than controlling motion. Consequently, features of the neuromusculoskeletal system that appear to be redundant or unnecessary for movement control can play a functional role in controlling dynamic behavior. Polyarticular muscles contribute to the mechanical impedance in a unique way. Skeletal redundancies have a profound influence on all aspects of dynamic behavior, including the apparent inertia of the limbs. Redundancies are commonly perceived as a complicating factor in the control of motion, a problem that must be solved by the central nervous system. Rather than presenting a problem requiring solution, they may present a solution to a problem. Posture is not merely the outcome of a motor act; it is one of the important preparatory stages in the production of motor behavior.
通过对运动协调的研究可以了解到很多关于中枢神经系统的知识，但只有在多关节系统中，其真正的丰富性和复杂性才会显现出来。尽管多关节动作具有内在的复杂性，但它们提供了一个以定量且可实验验证的方式了解中枢神经系统的绝佳机会。例如，观察到无约束、未受干扰的手臂运动在手的运动方面是协调的，这表明运动控制是按照抽象程度不断提高的层次进行组织的。这些手臂运动的组织方式就好像一只脱离身体的手可以在空间中移动；那么如何实现这一点的细节必须由层次结构中的不同层次来提供。人类行为的本质在于其适应性。正如协调的真正复杂性仅在多关节动作中才明显一样，适应性行为的精巧和微妙也仅在动态、交互式任务中才明显。仅研究运动不足以理解这种行为。肢体的动态反应成为首要关注点，并且必须由中枢神经系统进行控制。肢体的动态反应通常与其姿势相关，而非其运动，但在诸如使用工具这样的功能性任务中，姿势动力学是动作不可或缺的一部分。这种对运动行为的观点能带来一些有用的见解。协调不仅仅是运动本身的问题；在多关节系统中，即使是姿势也需要协调和控制。肌肉不仅仅是相互作用以在关节周围产生力；肢体的净机械阻抗可以通过包括拮抗肌在内的所有肌肉的协同激活来控制。控制动态行为比控制运动要求高得多。因此，神经肌肉骨骼系统中那些对于运动控制看似多余或不必要的特征，在控制动态行为中可能发挥功能性作用。多关节肌肉以独特的方式对机械阻抗做出贡献。骨骼冗余对动态行为的各个方面都有深远影响，包括肢体的表观惯性。冗余通常被视为运动控制中的一个复杂因素，是中枢神经系统必须解决的一个问题。它们并非呈现一个需要解决的问题，反而可能是一个问题的解决方案。姿势不仅仅是一个运动行为的结果；它是运动行为产生过程中的重要准备阶段之一。
