Department of Physical Therapy and Human Movement Sciences, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA.
Exp Brain Res. 2011 Feb;208(4):557-67. doi: 10.1007/s00221-010-2504-z. Epub 2010 Dec 12.
During the initiation of stepping, anticipatory postural adjustments (APAs) for lateral weight transfer and propulsion normally precede the onset of locomotion. In Parkinson's disease (PD), impaired step initiation typically involves altered APA ground force production with delayed step onset and deficits in stepping performance. If, as in stance and gait, sensory information about lower limb load is important for the control of stepping, then perturbations influencing loading conditions could affect the step initiation process. This study investigated the influence of changes in lower limb loading during step initiation in patients with PD and healthy control subjects. Participants performed rapid self-triggered step initiation with the impending single stance limb positioned over a pneumatically actuated platform. In perturbation trials, the stance limb ground support surface was either moved vertically downward (DROP) or upward (ELEVATE) by 1.5 cm shortly after the onset of the APA phase. Overall, PD patients demonstrated a longer APA duration, longer time to first step onset, and slower step speed than controls. In both groups, the DROP perturbation reinforced the intended APA kinetic changes for lateral weight transfer and resulted in a significant reduction in APA duration, increase in peak amplitude, and earlier time to first step onset compared with other conditions. During ELEVATE trials that opposed the intended weight transfer forces both groups rapidly adapted their stepping to preserve standing stability by decreasing step length and duration, and increasing step height and foot placement laterally. The findings suggested that sensory information associated with limb load and/or foot pressure modulates the spatial and temporal parameters of posture and locomotion components of step initiation in interaction with a centrally generated feedforward mode of neural control. Moreover, impaired step initiation in PD may at least acutely be enhanced by augmenting the coupling between posture and locomotion.
在开始迈步时，预期姿势调整（APAs）通常会先于运动发生，以进行侧向的重量转移和推进。在帕金森病（PD）中，起始步幅的障碍通常涉及到 APA 地面力产生的改变，从而导致步幅起始延迟和步幅表现缺陷。如果像在站立和行走中一样，下肢负载的感觉信息对步幅控制很重要，那么影响负载条件的干扰可能会影响步幅起始过程。本研究调查了 PD 患者和健康对照组在开始迈步时下肢负载变化对步幅起始的影响。参与者用即将处于单支撑位的下肢在气动驱动平台上进行快速自我触发的步幅起始。在干扰试验中，支撑肢的地面支撑面在 APA 阶段开始后不久会垂直向下（DROP）或向上（ELEVATE）移动 1.5 厘米。总的来说，PD 患者的 APA 持续时间较长，第一步的起始时间较长，步速较慢。在两组中，DROP 干扰都加强了预期的侧向重量转移的 APA 动力学变化，导致 APA 持续时间明显缩短，峰值幅度增加，并且与其他条件相比，第一步的起始时间更早。在 ELEVATE 试验中，与预期的重量转移力相反，两组都通过减少步幅和持续时间，增加步高和脚的侧向放置，快速适应以保持站立稳定性。这些发现表明，与肢体负载和/或脚压相关的感觉信息会调节姿势和运动成分的时空参数，与中枢产生的前馈神经控制模式相互作用。此外，PD 患者的起始步幅障碍至少可以通过增强姿势和运动之间的耦合来急性增强。
