Abstract：
Passive hamstring stiffness varies proximo-distally, resulting in inhomogeneous tissue strain during stretching that may affect localized adaptations and risk of muscle injuries. The purpose of the present study was to determine the acute and chronic effects of static stretching (SS) on intramuscular hamstring stiffness. Thirty healthy active participants had acute changes in passive biceps femoris (BF), semimembranosus (SM), and semitendinosus (ST) stiffness measured at 25% (proximal), 50% (middle), and 75% (distal) muscle length, using shear-wave elastography, immediately after SS. Participants then completed 4 weeks of either a SS intervention (n = 15) or no intervention (CON, n = 15) with stiffness measured before and after the interventions. The acute and chronic effects of SS were compared between anatomical regions and between regions on the basis of their relative stiffness pre-intervention. Acutely, SS decreased stiffness throughout the BF and SM (p ≤ 0.05) but not the ST (p = 0.326). However, a regional effect of stretching was observed for SM and ST with greater reduction in stiffness occurring in stiffer muscular regions (p = 0.001-0.013). Chronically, SS increased BF and ST (p < 0.05), but not SM (p = 0.422) stiffness compared with CON, but no regional effect of stretching was observed in any muscle (p = 0.361-0.833). SS resulted in contrasting acute and chronic effects, acutely decreasing stiffness in stiffer regions while chronically increasing stiffness. These results indicate that the acute effects of SS vary along the muscle\'s length on the basis of the relative stiffness of the muscle and that acute changes in stiffness from SS are unrelated to chronic adaptations.
摘要：
被动腿筋刚度在近端和远端变化，导致拉伸过程中不均匀的组织应变，可能影响局部适应和肌肉损伤的风险。本研究的目的是确定静态拉伸（SS）对肌内腿筋刚度的急性和慢性影响。30名健康的积极参与者在被动股二头肌（BF）中出现了急性变化，半膜（SM），和半腱肌（ST）刚度测量在25％（近端），50%(中),和75%（远端）肌肉长度，使用剪切波弹性成像，在SS之后。然后参与者完成了4周的SS干预(n=15)或无干预(CON，n=15），在干预前后测量刚度。根据干预前的相对僵硬度，比较了解剖区域之间和区域之间SS的急性和慢性影响。绝对,SS降低了整个BF和SM的刚度（p≤0.05），而不是ST（p=0.326）。然而,对于SM和ST，观察到拉伸的区域效应，在较硬的肌肉区域中刚度降低更大（p=0.001-0.013）。长期而言,SS增加BF和ST（p<0.05），但不是SM(p=0.422)刚度与CON相比，但是在任何肌肉中均未观察到拉伸的区域效应（p=0.361-0.833）。SS导致不同的急性和慢性影响，刚性区域的刚度急剧降低，而刚度则长期增加。这些结果表明，根据肌肉的相对刚度，SS的急性作用沿肌肉的长度变化，并且SS的刚度的急性变化与慢性适应无关。
