Tianjin Key Lab of Exercise Physiology and Sports Medicine, Department of Health and Exercise Science, Tianjin University of Sport, 51 Weijin South Street, Hexi District, Tianjin, 300381, China.
Institute of Sports and Health Science, 3-10-31, Kagamiyama, Higashi-hiroshima, Hiroshima, 739-0046, Japan.
Eur J Appl Physiol. 2017 Jan;117(1):201-211. doi: 10.1007/s00421-016-3514-8. Epub 2016 Dec 21.
We explored changes in muscle interactions during healthy aging as a window into neural control strategies of postural preparation to action/perturbation. In particular, we quantified the strength of multi-muscle synergies stabilizing the center of pressure (COP) displacement during the preparation for making a step associated with support surface translations.
Young and elderly subjects were required to make a step in response to support surface perturbations. Surface muscle activity of 11 leg and trunk muscles was analyzed to identify sets of 4 muscle modes (M-modes). Linear combinations of M-modes and their relationship to changes in the COP displacement in the anterior-posterior direction were then determined. Uncontrolled manifold analysis was performed to determine variance components in the M-mode space and indices of M-mode synergy stabilizing COP displacement.
Prior to the step initiation, the older subjects showed strong synergies that stabilized COP displacement to forward perturbation of the support surface. However, the synergy indices were significantly lower than those of the young subjects during preparation for making a step. The timings of early postural adjustment (EPA) and anticipatory postural adjustment (APA) were consistently earlier in the young subjects as compared to the older subjects. For both groups, the timing of EPA did not change across tasks, while APA showed delayed timing in response to the support surface translations.
We infer that changes in the indices of synergies with age may present challenges for the control of postural preparation to external perturbation in older adults. They may lead to excessive muscle co-contractions and low stability of COP displacement. The results reported here could have clinical relevance when identifying the risk of making a step, which has been linked to an increased risk of falls among the elderly.
我们探讨了健康衰老过程中肌肉相互作用的变化，以此了解对姿势准备进行动作/扰动的神经控制策略。具体而言，我们量化了在准备进行与支撑面平移相关的步行动作时稳定身体重心（COP）位移的多肌肉协同作用的强度。
要求年轻和老年受试者在支撑面扰动时进行步行动作。分析 11 个腿部和躯干肌肉的表面肌肉活动，以确定 4 个肌肉模式（M-模式）的集合。然后确定 M-模式的线性组合及其与前-后向 COP 位移变化的关系。进行非受控流形分析，以确定 M-模式空间中的方差分量和稳定 COP 位移的 M-模式协同作用指数。
在步行动作开始之前，老年受试者表现出强大的协同作用，可稳定支撑面向前扰动时的 COP 位移。然而，协同作用指数在准备进行步行动作时明显低于年轻受试者。与年轻受试者相比，早期姿势调整（EPA）和预测性姿势调整（APA）的时间在老年受试者中始终更早。对于两个组，EPA 的时间在任务之间没有变化，而 APA 在响应支撑面平移时显示出延迟的时间。
我们推断，随着年龄的增长，协同作用指数的变化可能会对老年人对外来干扰的姿势准备控制提出挑战。它们可能导致过度的肌肉协同收缩和 COP 位移稳定性降低。当识别与老年人跌倒风险增加相关的步行动作风险时，这里报告的结果可能具有临床相关性。
