Background

Age-related changes of human gait characteristics associated with muscle weakness have been reported in previous studies. Human gait is considered as a cyclic motion adapted to individual body-characteristics and the surrounding-environment based on motion criteria. Based on this hypothesis, elderly gait characteristics may be caused by an adaptation to muscle weakness.

Research question

What role does gait adaptation to muscle weakness play in the development of elderly gait, and what criteria are used in elderly gait adaptation?

Methods

We examined the effects of gait adaptation to muscle weakness on steady gait characteristics using computational forward dynamics simulation with a two-dimensional neuro-musculo-skeletal model. For gait adaptation, we tested two motion criteria: (i) energy cost minimization, which is a widely used criterion for healthy adults; and (ii) energy rate minimization, based on existing measurements of elderly gait characteristics.

Results

Progression of muscle weakness enhanced the reduction of joint angle motion and minimum toe clearance, and finally resulted in falling. Gait adaptation to muscle weakness successfully formed stable walking patterns regardless of motion criteria, even at muscle weakness of 30 %, which represents a moderate degree of elderly muscle weakness. When criterion (i) was used, the time courses of joint motion were similar to those of healthy adults and a relatively high level of muscle activation was found in the whole gait cycle to compensate for muscle weakness. When criterion (ii) was used, the muscle activity level was lower than that of criterion (i) to minimize the energy rate, and the constructed gait successfully captured the characteristics of elderly gait reported in previous studies.

Significance

These findings suggest that gait adaptation to muscle weakness plays an essential role in the development of stable gait characteristics, whereas elderly people might use a different motion criterion compared with healthy adults in gait adaptation.

中文翻译：

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老年人步态对肌肉无力的步态适应的二维正向动力学模拟

背景

在先前的研究中已经报道了与肌肉无力相关的与步态有关的年龄变化。人的步态被认为是基于运动标准适应个体身体特征和周围环境的循环运动。基于此假设，老年人的步态特征可能是由于对肌肉无力的适应引起的。

研究问题

步态适应肌肉无力在老年人步态发展中起什么作用，老年人步态适应采用什么标准？

方法

我们使用二维神经-肌肉-骨骼模型通过计算前向动力学模拟，研究了对肌肉无力的步态适应对稳定步态特征的影响。为了适应步态，我们测试了两个运动标准：（i）最小化能量消耗，这是健康成年人广泛使用的标准；（ii）根据现有的老年人步态特征测量结果，将能量率最小化。

结果

肌肉无力的进展增强了关节角运动的减少和最小的脚趾间隙，最终导致跌倒。不管运动标准如何，对肌肉无力的步态适应都成功地形成了稳定的步行模式，即使在30％的肌肉无力的情况下，也代表了老年人中等程度的肌肉无力。当使用标准（i）时，关节运动的时程与健康成年人的相似，并且在整个步态周期中发现了较高水平的肌肉激活以补偿肌肉无力。使用标准（ii）时，肌肉活动水平低于标准（i），以最大程度地降低能量消耗，并且步态成功捕获了先前研究报告的老年人步态特征。

意义

这些发现表明，对肌肉无力的步态适应在稳定步态特征的发展中起着至关重要的作用，而与健康成年人相比，老年人在步态适应中可能使用不同的运动标准。