Reactive stepping capacity to recover from a loss of balance declines with aging, which increases the risk of falling. To gain insight into the underlying mechanisms, we investigated whether muscle coordination patterns of reactive stepping differed between healthy young and older individuals. We performed a cross-sectional study between 15 healthy young and 14 healthy older adults. They recovered from 200 multidirectional platform translations that evoked reactive stepping responses. We determined spatiotemporal step variables and used muscle synergy analysis to characterize stance- and swing-leg muscle coordination patterns from the start of perturbation until foot landing. We observed delayed step onsets in older individuals, without further spatiotemporal differences. Muscle synergy structure was not different between young and older individuals, but age-related differences were observed in the time-varying synergy activation patterns. In anterior-posterior directions, the older individuals demonstrated significantly enhanced early swing-leg synergy activation consistent with non-stepping behavior. In addition, around step onset they demonstrated increased levels of synergy coactivation (mainly around the ankle) in lateral and anterior directions, which did not appear to hamper foot clearance. Although synergy structure was not affected by age, the delayed step onsets and the enhanced early synergy recruitment point at a relative bias towards non-stepping behavior in older adults. They may need more time for accumulating information on the direction of perturbation and making the corresponding sensorimotor transformations before initiating the step. Future work may investigate whether perturbation-based training improves these age-related deficits.

中文翻译：

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从失去平衡中恢复的迈步反应的肌肉协调模式与年龄相关的变化

随着年龄的增长，从失去平衡中恢复的反应性迈步能力会下降，从而增加跌倒的风险。为了深入了解潜在机制，我们研究了健康年轻人和老年人之间反应性迈步的肌肉协调模式是否不同。我们对 15 名健康年轻人和 14 名健康老年人进行了横断面研究。他们从 200 次引发反应性步进反应的多向平台翻译中恢复过来。我们确定了时空步骤变量，并使用肌肉协同分析来表征从扰动开始到脚落地的站立和摆动腿肌肉协调模式。我们观察到老年人的迈步延迟，没有进一步的时空差异。年轻人和老年人之间的肌肉协同结构没有差异，但随时间变化的协同激活模式观察到与年龄相关的差异。在前后方向上，老年人表现出与非迈步行为一致的早期摆腿协同激活显着增强。此外，在迈步开始前后，他们表现出横向和前向协同共激活水平（主要是脚踝周围）的增加，这似乎并没有妨碍足部间隙。尽管协同结构不受年龄的影响，但迈步开始的延迟和早期协同募集的增强表明老年人对不迈步行为的相对偏向。在开始该步骤之前，他们可能需要更多时间来积累有关扰动方向的信息并进行相应的感觉运动转换。未来的工作可能会调查基于扰动的训练是否可以改善这些与年龄相关的缺陷。