Kingma I, Toussaint H M, Commissaris D A, Savelsbergh G J
Institute for Fundamental and Clinical Human Movement Sciences, Faculty of Human Movement Sciences, Vrije Universiteit, Amsterdam, The Netherlands.
Exp Brain Res. 1999 Mar;125(1):35-42. doi: 10.1007/s002210050655.
Human balance in stance is usually defined as the preservation of the vertical projection of the center of mass (COM) on the support area formed by the feet. Under microgravity conditions, the control of equilibrium seems to be no longer required. However, several reports indicate preservation of COM control in tasks such as arm or leg raising, tiptoe standing, or trunk bending. It is still unclear whether COM control is also maintained in complex multijoint movements during short term exposure to microgravity. In the current study, the dynamics of equilibrium control were studied in four subjects performing two series of seven whole-body lifting movements under microgravity during parabolic flights. The aims of the study were to examine whether the trajectory of horizontal COM motion during lifting movements changes in short-term exposure to microgravity and whether there is any sign of recovery after several lifting movements. It was found that, compared with control movements under normal gravity, the horizontal position of the COM was shifted backward during the entire lifting movement in all subjects. In the second series of lifting movements under microgravity, a partial recovery of the COM trajectory toward the normal gravity situation was found. Under microgravity, angles of the ankle, knee, hip, and lumbar joints differed significantly from the angles found under normal gravity. Recovery of joint angular trajectories in the second series of lifting movements mainly occurred for those angles that could contribute to a reduction of the backward COM shift. It is to be pointed out that COM control under microgravity is not redundant but functional. Persisting COM control under microgravity may be required for pure mechanical reasons, since rotational movements of the body are dependent on adequate control of the COM position with respect to external forces. It is shown that, from a mechanical perspective, subjects can benefit from a backward displacement of the COM in the downward as well as the upward phase of the lifting movement under microgravity.
人体站立时的平衡通常被定义为质心（COM）在由双脚形成的支撑区域上的垂直投影得以保持。在微重力条件下，似乎不再需要平衡控制。然而，有几份报告表明，在诸如举臂或抬腿、踮脚尖站立或躯干弯曲等任务中，质心控制得以保留。目前尚不清楚在短期暴露于微重力环境下的复杂多关节运动中，质心控制是否也能维持。在当前的研究中，对四名受试者在抛物线飞行的微重力环境下进行的两组七次全身举升运动中的平衡控制动力学进行了研究。该研究的目的是检查在短期暴露于微重力环境下举升运动过程中水平质心运动轨迹是否发生变化，以及在几次举升运动后是否有恢复的迹象。研究发现，与正常重力下的对照运动相比，所有受试者在整个举升运动过程中质心的水平位置都向后移动。在微重力下的第二组举升运动中，发现质心轨迹部分恢复到正常重力情况下的轨迹。在微重力下，踝关节、膝关节、髋关节和腰椎关节的角度与正常重力下的角度有显著差异。第二组举升运动中关节角度轨迹的恢复主要发生在那些有助于减少质心向后移动的角度上。需要指出的是，微重力下的质心控制并非多余，而是具有功能性。由于身体的旋转运动取决于相对于外力对质心位置的适当控制，从纯粹的机械原因来看，微重力下持续的质心控制可能是必要的。结果表明，从机械角度来看，在微重力下举升运动的向下和向上阶段，受试者可以从质心向后位移中受益。
