BACKGROUND Range of motion restriction following immobilization is spontaneously recovered at least in part by remobilization. However, the mechanisms underlying how muscles change with range of motion recovery are poorly understood. This study aimed to reveal morphological and biomechanical changes in the knee flexor semitendinosus muscle that contribute to knee joint contracture following the relief of immobilization. METHODS To induce flexion contracture, we immobilized rat right knees by an external fixator at a flexed position for three weeks. After removal of the fixator, the joints were allowed to move freely (remobilization) for up to 14 days. We obtained muscle length and passive stiffness of the isolated semitendinosus muscles after measuring passive knee extension range of motion. FINDINGS Three weeks of immobilization induced range of motion reduction, as well as changes in morphological and biomechanical properties of the semitendinosus muscle, such as reduced muscle length and increment of passive stiffness leading to myogenic contracture. Joint immobilization-induced reduction of range of motion, representing flexion contracture, was partially reduced by 14 days of remobilization. Concomitantly, both muscle length and muscle stiffness returned to levels not significantly different from those in the contralateral side during this period. INTERPRETATION These results suggest that improvement of myogenic contracture during the early phase of remobilization occurs via both morphological and biomechanical adaptations.

中文翻译：

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固定在大鼠体内后，骨骼肌在恢复阶段的形态和生物力学适应性。

背景技术固定后的运动限制范围至少部分地通过固定自发地恢复。但是，人们对肌肉如何随运动恢复范围变化的机制了解得很少。这项研究的目的是揭示膝关节屈曲半腱肌的形态和生物力学变化，这些变化有助于固定后膝关节挛缩。方法为了诱发屈曲挛缩，我们用屈伸位置的外固定器将大鼠右膝固定了三个星期。移除固定器后，允许关节自由移动（固定）长达14天。在测量被动膝盖伸展运动范围后，我们获得了孤立的半腱肌的肌肉长度和被动刚度。研究发现，固定三周后，运动范围减小，半腱肌的形态和生物力学特性发生变化，例如，肌肉长度减少和被动僵硬增加导致肌源性挛缩。关节固定导致的运动范围减少（代表屈曲挛缩）在移动14天后被部分减少。同时，在此期间，肌肉长度和肌肉僵硬度恢复到与对侧相同的水平。解释这些结果表明，通过形态和生物力学的适应，在早期的移植过程中肌源性挛缩的改善。以及半腱肌的形态和生物力学特性的变化，例如，肌肉长度减少和被动僵硬的增加导致肌源性挛缩。关节固定导致的运动范围减少（代表屈曲挛缩）在移动14天后被部分减少。同时，在此期间，肌肉长度和肌肉僵硬度恢复到与对侧相同的水平。解释这些结果表明，通过形态和生物力学的适应，在早期的移植过程中肌源性挛缩的改善。以及半腱肌的形态和生物力学特性的变化，例如，肌肉长度减少和被动僵硬增加导致肌源性挛缩。关节固定导致的运动范围减少，代表屈曲挛缩，在移动14天后部分减少。同时，在此期间，肌肉长度和肌肉僵硬度恢复到与对侧相同的水平。解释这些结果表明，通过形态和生物力学的适应，在早期的移植过程中肌源性挛缩的改善。代表屈曲挛缩的患者，经过14天的修复后部分减少。同时，在此期间，肌肉长度和肌肉僵硬度恢复到与对侧相同的水平。解释这些结果表明，通过形态和生物力学的适应，在早期的移植过程中肌源性挛缩的改善。代表屈曲挛缩的患者，经过14天的修复后部分减少。同时，在此期间，肌肉长度和肌肉僵硬度恢复到与对侧相同的水平。解释这些结果表明，通过形态和生物力学的适应，在早期的移植过程中肌源性挛缩的改善。