Gélat Thierry, Le Pellec Armande
Laboratoire Sport et Culture, EA 2931, Equipe Physiologie et Biomécanique des Mouvements Naturels et des Gestes Sportifs, UFR STAPS Paris X Nanterre, France.
Neurosci Lett. 2007 Dec 11;429(1):17-21. doi: 10.1016/j.neulet.2007.09.054. Epub 2007 Oct 2.
The study examined why anticipatory postural adjustments (APA) associated to gait initiation in a stepping up to a new level situation (SU) are reduced as compared to a level walking situation (LW), as previously reported. Five young adults performed gait initiation in both situations at normal and fast speed. Data from a force platform provided gait parameters related to the motion of the body's centre of mass (CM) on the anteroposterior (progression) and vertical axes. The electromyographic activity of the soleus of the stance limb (SOst) and the vastus lateralis of the swing limb (VLsw) were analyzed prior to and after the onset of the double stance phase. The results showed that APA and progression CM velocity at the time of foot contact were smaller in SU, whereas the peak of this velocity was similar in both situations. Thus, the change in progression velocity during the double stance phase had to be greater in SU than in LW. In both velocity conditions, the activity of SOst stopped after the time of foot contact in both situations, but clearly later in SU. So, this ankle plantar flexor muscle would be involved not only in the change of body lift but also in forward CM progression. The latter role of this muscle brought supporting evidence for the reduction of APA in SU, enabling the peak of progression velocity to be similar in both situations. Only in SU, the timing of activation of VLsw and deactivation of SOst strongly co-varied, showing the implementation of a motor synergy to fulfil the new requirements of the task, i.e. body lift.
如先前报道，本研究探讨了为何在迈上一个新高度的情境（SU）中，与步态起始相关的预期姿势调整（APA）相较于在水平行走情境（LW）中会减少。五名年轻成年人在这两种情境下以正常速度和快速速度进行步态起始。来自测力平台的数据提供了与身体重心（CM）在前后（行进）和垂直轴上的运动相关的步态参数。在双支撑相开始之前和之后，分析了支撑腿比目鱼肌（SOst）和摆动腿股外侧肌（VLsw）的肌电活动。结果表明，在SU中，足部接触时的APA和行进CM速度较小，而该速度的峰值在两种情境中相似。因此，SU中双支撑相期间行进速度的变化必须大于LW。在两种速度条件下，两种情境中SOst的活动在足部接触后均停止，但在SU中明显更晚。所以，这块踝关节跖屈肌不仅会参与身体抬升的变化，还会参与CM向前行进。该肌肉的后一种作用为SU中APA的减少提供了支持证据，使得两种情境中行进速度的峰值相似。仅在SU中，VLsw的激活时间和SOst的失活时间强烈协变，表明实施了一种运动协同作用以满足任务的新要求，即身体抬升。
