Newman D J, Jackson D K, Bloomberg J J
Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge 02139, USA.
Exp Brain Res. 1997 Oct;117(1):30-42. doi: 10.1007/pl00005788.
Astronauts exposed to the microgravity conditions encountered during space flight exhibit postural and gait instabilities upon return to earth that could impair critical postflight performance. The aim of the present study was to determine the effects of microgravity exposure on astronauts' performance of two-footed jump landings. Nine astronauts from several Space Shuttle missions were tested both preflight and postflight with a series of voluntary, two-footed downward hops from a 30-cm-high step. A video-based, three-dimensional motion-analysis system permitted calculation of body segment positions and joint angular displacements. Phase-plane plots of knee, hip, and ankle angular velocities compared with the corresponding joint angles were used to describe the lower limb kinematics during jump landings. The position of the whole-body center of mass (COM) was also estimated in the sagittal plane using an eight-segment body model. Four of nine subjects exhibited expanded phase-plane portraits postflight, with significant increases in peak joint flexion angles and flexion rates following space flight. In contrast, two subjects showed significant contractions of their phase-plane portraits postflight and three subjects showed insignificant overall changes after space flight. Analysis of the vertical COM motion generally supported the joint angle results. Subjects with expanded joint angle phase-plane portraits postflight exhibited larger downward deviations of the COM and longer times from impact to peak deflection, as well as lower upward recovery velocities. Subjects with postflight joint angle phase-plane contraction demonstrated opposite effects in the COM motion. The joint kinematics results indicated the existence of two contrasting response modes due to microgravity exposure. Most subjects exhibited "compliant" impact absorption postflight, consistent with decreased limb stiffness and damping, and a reduction in the bandwidth of the postural control system. Fewer subjects showed "stiff" behavior after space flight, where contractions in the phase-plane portraits pointed to an increase in control bandwidth. The changes appeared to result from adaptive modifications in the control of lower limb impedance. A simple 2nd-order model of the vertical COM motion indicated that changes in the effective vertical stiffness of the legs can predict key features of the postflight performance. Compliant responses may reflect inflight adaptation due to altered demands on the postural control system in microgravity, while stiff behavior may result from overcompensation postflight for the presumed reduction in limb stiffness inflight.
在太空飞行中经历微重力环境的宇航员返回地球后会出现姿势和步态不稳定的情况，这可能会损害飞行后的关键表现。本研究的目的是确定微重力暴露对宇航员双脚跳跃着陆表现的影响。对来自几次航天飞机任务的九名宇航员在飞行前和飞行后进行了测试，让他们从30厘米高的台阶上进行一系列自愿的双脚向下跳跃。基于视频的三维运动分析系统允许计算身体各节段的位置和关节角位移。将膝盖、臀部和脚踝的角速度与相应关节角度的相平面图用于描述跳跃着陆过程中的下肢运动学。还使用八节段身体模型在矢状面估计全身质心（COM）的位置。九名受试者中有四名在飞行后表现出相平面图扩展，飞行后关节最大屈曲角度和屈曲速率显著增加。相比之下，两名受试者在飞行后表现出相平面图显著收缩，三名受试者在飞行后总体变化不显著。对垂直COM运动的分析总体上支持了关节角度结果。飞行后关节角度相平面图扩展的受试者表现出COM更大的向下偏差以及从撞击到最大偏转的时间更长，还有更低的向上恢复速度。飞行后关节角度相平面图收缩的受试者在COM运动中表现出相反的效果。关节运动学结果表明，由于微重力暴露存在两种截然不同的反应模式。大多数受试者在飞行后表现出“顺应性”冲击吸收，这与肢体刚度和阻尼降低以及姿势控制系统带宽减小一致。较少受试者在太空飞行后表现出“僵硬”行为，相平面图收缩表明控制带宽增加。这些变化似乎是由于下肢阻抗控制的适应性改变所致。垂直COM运动的一个简单二阶模型表明，腿部有效垂直刚度的变化可以预测飞行后表现的关键特征。顺应性反应可能反映了由于微重力环境下对姿势控制系统需求改变而导致的飞行中适应性变化，而僵硬行为可能是由于飞行后对飞行中肢体刚度假定降低的过度补偿所致。
