Hughey Lucinda K, Fung Joyce
School of Physical & Occupational Therapy, McGill University, 3654 Prom. Sir William Osler, Montreal, Quebec, Canada, H3G 1Y5.
Exp Brain Res. 2005 Aug;165(2):152-66. doi: 10.1007/s00221-005-2295-9. Epub 2005 Jun 7.
The aim of the present study was to investigate the relationship between proactive and reactive components of postural control. We contrasted the kinematic and electromyographic (EMG) responses to multidirectional voluntary leg lifts with those elicited by unexpected surface tilts. In particular, we addressed the role of trunk stabilization following either a voluntary or forced weight shift from double to single limb support. Nine young female subjects stood with a standing posture of 45 degrees toe-out and their arms abducted to shoulder level. On the experimenter's signal, subjects either (1) lifted one leg as fast as possible in one of six directions (R/L side, R/L diagonal front, R/L diagonal back) to a height of 45 degrees or (2) maintained standing as the support surface tilted at a rate of 53 degrees /s to a height of 10 degrees in one of six directions (R/L-up, R/L diagonal toes-up, R/L diagonal toes-down). For both tasks, our results showed that the center of pressure (COP) displacement began before or in conjunction with displacement of the center of mass (COM), after which the COP oscillated about the horizontal projection of the COM. In addition, the muscles were recruited in a distal-to-proximal sequence, either in anticipation of the voluntary leg lift or in response to the sudden surface tilt. Thus, the COP was being used dynamically to control displacement of the COM. The axial postural strategy comprising head, trunk, and pelvis movements was quantified by means of principal component analysis. More than 95% of the variance in the data could be described by the first two eigenvectors, which revealed specific coordination patterns dominated by pelvis rotation in one direction and head/trunk rotation in the opposite direction. Unexpected surface tilting elicited an automatic response strategy that focused on controlling the orientation of the head and trunk with respect to the vertical gravity vector while trunk verticality was compromised for movement generation and the recovery of postural equilibrium during leg lifting. In conclusion, regardless of the type (voluntary versus involuntary) or direction of perturbation, the strategy employed by the central nervous system to control the body COM displacement concerns mainly trunk stabilization.
本研究的目的是调查姿势控制中主动和反应成分之间的关系。我们将多方向自愿抬腿的运动学和肌电图（EMG）反应与意外表面倾斜引起的反应进行了对比。特别是，我们探讨了从双腿支撑到单腿支撑的自愿或强制体重转移后躯干稳定的作用。九名年轻女性受试者以双脚外展45度的站立姿势站立，双臂外展至肩部水平。在实验者发出信号后，受试者要么（1）在六个方向（右/左侧、右/左前对角线、右/左后对角线）中的一个方向尽快抬起一条腿至45度高度，要么（2）在支撑面以53度/秒的速度在六个方向（右/上、右/左脚趾向上对角线、右/左脚趾向下对角线）中的一个方向倾斜至10度高度时保持站立。对于这两项任务，我们的结果表明，压力中心（COP）位移在质心（COM）位移之前或与之同时开始，之后COP围绕COM的水平投影振荡。此外，无论是预期自愿抬腿还是对突然的表面倾斜做出反应，肌肉都是按照从远端到近端的顺序募集的。因此，COP被动态地用于控制COM的位移。通过主成分分析对包括头部、躯干和骨盆运动的轴向姿势策略进行了量化。数据中超过95%的方差可以由前两个特征向量描述，这两个特征向量揭示了特定的协调模式，主要由一个方向的骨盆旋转和相反方向的头部/躯干旋转主导。意外的表面倾斜引发了一种自动反应策略，该策略侧重于控制头部和躯干相对于垂直重力向量的方向，而在抬腿过程中为了产生运动和恢复姿势平衡，躯干垂直度会受到影响。总之，无论扰动的类型（自愿与非自愿）或方向如何，中枢神经系统用于控制身体COM位移的策略主要涉及躯干稳定。
