Vernooij Carlijn A, Rao Guillaume, Berton Eric, Retornaz Frédérique, Temprado Jean-Jacques
Aix Marseille University, CNRS, ISM Marseille, France.
Centre Gérontologique Départemental Marseille, France.
Front Aging Neurosci. 2016 Dec 21;8:309. doi: 10.3389/fnagi.2016.00309. eCollection 2016.
Aging leads to alterations not only within the complex subsystems of the neuro-musculo-skeletal system, but also in the coupling between them. Here, we studied how aging affects functional reorganizations that occur both within and between the behavioral and muscular levels, which must be coordinated to produce goal-directed movements. Using unimanual reciprocal Fitts' task, we examined the behavioral and muscular dynamics of older adults (74.4 ± 3.7 years) and compared them to those found for younger adults (23.2 ± 2.0 years). To achieve this objective, we manipulated the target size to trigger a phase transition in the behavioral regime and searched for concomitant signatures of a phase transition in the muscular coordination. Here, muscular coordination was derived by using the method of muscular synergy extraction. With this technique, we obtained functional muscular patterns through non-negative matrix factorization of the muscular signals followed by clustering the resulting synergies. Older adults showed a phase transition in behavioral regime, although, in contrast to young participants, their kinematic profiles did not show a discontinuity. In parallel, muscular coordination displayed two typical signatures of a phase transition, that is, increased variability of coordination patterns and a reorganization of muscular synergies. Both signatures confirmed the existence of muscular reorganization in older adults, which is coupled with change in dynamical regime at behavioral level. However, relative to young adults, transition occurred at lower index of difficulty (ID) in older participants and the reorganization of muscular patterns lasted longer (over multiple IDs). This implies that consistent changes occur in coordination processes across behavior and muscle. Furthermore, the repertoire of muscular patterns was reduced and somewhat modified for older adults, relative to young participants. This suggests that aging is not only related to changes in individual muscles (e.g., caused by dynapenia) but also in their coordination.
衰老不仅会导致神经 - 肌肉 - 骨骼系统复杂子系统内部发生变化，还会影响这些子系统之间的耦合。在此，我们研究了衰老如何影响行为和肌肉层面内部以及它们之间发生的功能重组，而这些重组必须相互协调才能产生目标导向的运动。我们使用单手往复式菲茨任务，研究了老年人（74.4 ± 3.7岁）的行为和肌肉动力学，并将其与年轻人（23.2 ± 2.0岁）的进行比较。为实现这一目标，我们通过操纵目标大小来触发行为状态的相变，并寻找肌肉协调中相变的伴随特征。在这里，肌肉协调是通过肌肉协同提取方法得出的。利用这项技术，我们通过对肌肉信号进行非负矩阵分解，然后对得到的协同作用进行聚类，从而获得功能性肌肉模式。老年人在行为状态上出现了相变，不过与年轻参与者不同的是，他们的运动学特征没有显示出不连续性。与此同时，肌肉协调表现出相变的两个典型特征，即协调模式的变异性增加和肌肉协同作用的重组。这两个特征都证实了老年人存在肌肉重组，且与行为层面动态状态的变化相关联。然而，相对于年轻人，老年人在较低的难度指数（ID）下就发生了转变，并且肌肉模式的重组持续时间更长（跨越多个ID）。这意味着行为和肌肉的协调过程发生了一致的变化。此外，相对于年轻参与者，老年人的肌肉模式种类有所减少且略有改变。这表明衰老不仅与单个肌肉的变化（例如由肌肉减少症引起）有关，还与它们的协调有关。
