Creath Robert, Kiemel Tim, Horak Fay, Peterka Robert, Jeka John
Department of Kinesiology, University of Maryland, College Park, MD 20742, USA.
Neurosci Lett. 2005 Mar 29;377(2):75-80. doi: 10.1016/j.neulet.2004.11.071. Epub 2004 Dec 19.
When standing quietly, human upright stance is typically approximated as a single segment inverted pendulum. In contrast, investigations which perturb upright stance with support surface translations or visual driving stimuli have shown that the body behaves like a two-segment pendulum, displaying both in-phase and anti-phase patterns between the upper and lower body. Here we present evidence that a single-segment characterization of quiet stance is inadequate. Similar to perturbed stance, quiet stance has simultaneously co-existing in-phase and anti-phase patterns. Subjects stood with eyes closed in three sensory conditions: a fixed surface, a foam surface, and a sway-referenced surface. Spectral analysis showed that the body behaved like a multi-link pendulum with two co-existing modes. The angles of the trunk and leg segments were in-phase for frequencies below 1 Hz and anti-phase for frequencies above 1Hz. The shift from in-phase to anti-phase sway showed an abrupt change for the fixed and foam surfaces, but a gradual change for the sway-referenced condition with the trunk showing a phase lead over the legs. The coexistence of in-phase and anti-phase patterns during quiet stance suggests that the ankle and hip strategies are not extremes along a behavioral continuum of mixed strategies. They are "simultaneously co-existing excitable modes", both always present, but one of which may predominate depending upon the characteristics of the available sensory information, task or perturbation.
安静站立时，人体直立姿势通常近似为单节段倒立摆。相比之下，通过支撑面平移或视觉驱动刺激干扰直立姿势的研究表明，身体的行为类似于双节段摆，上半身和下半身之间呈现同相和反相模式。在此，我们提供证据表明，用单节段来描述安静站立姿势是不够的。与受干扰的站立姿势类似，安静站立姿势同时存在同相和反相模式。受试者在三种感觉条件下闭眼站立：固定表面、泡沫表面和摇摆参考表面。频谱分析表明，身体的行为类似于具有两种共存模式的多连杆摆。对于频率低于1Hz的情况，躯干和腿部节段的角度是同相的，而对于频率高于1Hz的情况则是反相的。对于固定表面和泡沫表面，从同相摇摆到反相摇摆的转变表现为突然变化，而对于摇摆参考条件则是逐渐变化，躯干相对于腿部呈现相位超前。安静站立时同相和反相模式的共存表明，踝关节和髋关节策略并非沿着混合策略的行为连续体的两个极端。它们是“同时共存的可激发模式”，两者始终存在，但其中一种可能根据可用感觉信息、任务或干扰的特征而占主导地位。
