BACKGROUND Muscle weakness is one of the most common motor impairments after stroke. A variety of progressive muscular changes are reported in chronic stroke survivors, and it is now feasible to consider these changes as an added source of weakness. However, the net contributions of such muscular changes towards muscle weakness have not been fully quantified. METHODS Accordingly, this study aims: (1) to compare muscle architecture of the human medial gastrocnemius between paretic and non-paretic sides in seven chronic hemispheric stroke survivors under passive conditions; (2) to characterize fascicle behavior (i.e., fascicle shortening and fascicle rotation) of the muscle during voluntary isometric contractions; and (3) to assess potential associations between muscle architectural parameters and muscle weakness. Muscle architecture of the medial gastrocnemius (including fascicle length, fascicle pennation angle, and muscle thickness) was characterized using B-mode ultrasonography, and fascicle behavior was then quantified as a function of isometric plantarflexion torque normalized to body mass. FINDINGS Our experimental results showed that under passive conditions, there was a significant difference in fascicle length and muscle thickness between paretic and non-paretic muscles, but no difference in resting fascicle pennation angle. However, during isometric contraction, both fascicle shortening and fascicle rotation on the paretic side were significantly decreased, compared to the non-paretic side. Moreover, the relative (i.e., paretic/non-paretic) fascicle rotation-shortening ratio (i.e., fascicle rotation per fascicle shortening) was strongly correlated with the relative maximum voluntary isometric plantarflexion torque. INTERPRETATION This association implies that such fascicle changes could impair the force-generating capacity of the muscle in chronic stroke survivors.

中文翻译：

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有限的束缩短和束旋转可能与慢性中风幸存者的腹肌中自愿的力量生成能力受损有关。

背景技术肌肉无力是中风后最常见的运动障碍之一。据报道，慢性卒中幸存者会出现各种进行性肌肉改变，现在可以将这些改变视为弱点的附加来源。然而，这种肌肉变化对肌无力的净贡献尚未完全量化。方法因此，本研究的目的是：（1）在被动条件下比较七个慢性半球性卒中幸存者的平腹侧和非平腹侧人腓肠肌的肌肉结构；（2）表征在等距收缩过程中肌肉的束行为（即束缩短和束旋转）；（3）评估肌肉结构参数与肌肉无力之间的潜在关联。使用B型超声对腓肠肌内侧的肌肉结构（包括束长度，束前倾角和肌肉厚度）进行表征，然后将束的行为量化为归一化为体重的等距plant屈扭矩的函数。结果我们的实验结果表明，在被动条件下，稀疏肌和非稀疏肌的束长度和肌肉厚度存在显着差异，而静止束垂度角度则无差异。但是，在等轴测收缩期间，与非顶侧相比，顶侧的束缩短和顶旋转都显着降低。而且，相对（即，稀疏/非稀疏）束旋转缩短比（即，每一短束缩短的短束旋转）与相对最大自愿等距足底屈曲扭矩密切相关。解释这种联系暗示着这种束改变可能损害慢性中风幸存者的肌肉产生力的能力。