Bioengineering Department, NearLab, Politecnico di Milano, P.za Leonardo Da Vinci 32, 20133 Milan, Italy.
Exp Brain Res. 2012 Jan;216(2):203-15. doi: 10.1007/s00221-011-2918-2. Epub 2011 Dec 8.
Many studies showed that both arm movements and postural control are characterized by strong invariants. Besides, when a movement requires simultaneous control of the hand trajectory and balance maintenance, these two movement components are highly coordinated. It is well known that the focal and postural invariants are individually tightly linked to gravity, much less is known about the role of gravity in their coordination. It is not clear whether the effect of gravity on different movement components is such as to keep a strong movement-posture coordination even in different gravitational conditions or whether gravitational information is necessary for maintaining motor synergism. We thus set out to analyze the movements of eleven standing subjects reaching for a target in front of them beyond arm's length in normal conditions and in microgravity. The results showed that subjects quickly adapted to microgravity and were able to successfully accomplish the task. In contrast to the hand trajectory, the postural strategy was strongly affected by microgravity, so to become incompatible with normo-gravity balance constraints. The distinct effects of gravity on the focal and postural components determined a significant decrease in their reciprocal coordination. This finding suggests that movement-posture coupling is affected by gravity, and thus, it does not represent a unique hardwired and invariant mode of control. Additional kinematic and dynamic analyses suggest that the new motor strategy corresponds to a global oversimplification of movement control, fulfilling the mechanical and sensory constraints of the microgravity environment.
许多研究表明，手臂运动和姿势控制都具有很强的不变性。此外，当一个运动需要同时控制手的轨迹和平衡维持时，这两个运动成分高度协调。众所周知，焦点和姿势不变性各自与重力紧密相关，但对它们协调中重力的作用知之甚少。尚不清楚重力对不同运动成分的影响是否足以保持强烈的运动-姿势协调，即使在不同的重力条件下，或者重力信息是否对维持运动协同作用是必要的。因此，我们着手分析 11 名站立受试者在正常条件和微重力下伸手伸向前方超出手臂长度的目标的运动。结果表明，受试者很快适应了微重力，并能够成功完成任务。与手轨迹相比，姿势策略受到微重力的强烈影响，因此与正常重力平衡约束不兼容。重力对焦点和姿势成分的明显影响导致它们的相互协调显著降低。这一发现表明，运动-姿势耦合受到重力的影响，因此，它不代表一种独特的硬连线和不变的控制模式。附加的运动学和动力学分析表明，新的运动策略对应于运动控制的全局简化，满足微重力环境的机械和感官约束。
