The pendulum test assesses quadriceps spasticity by dropping the lower leg of a relaxed patient from the horizontal position and observing limb movement. The first swing excursion (FS) decreases with increasing spasticity severity. Our recent simulation study suggests that the reduced initial swing results from muscle short-range stiffness and its interaction with reflex hyper-excitability. Short-range stiffness emerges from the thixotropic behavior of muscles where fiber stiffness upon stretch increases when the muscle is held isometric. Fiber stiffness might thus be higher during the first swing of the pendulum test than during consecutive swings. In addition, it has recently been suggested that muscle spindle firing reflects fiber force rather than velocity and therefore, reflex activity might depend on fiber stiffness. If this hypothesized mechanism is true, we expect to observe larger first swing excursions and reduced reflex muscle activity when the leg is moved rather than kept isometric before release, especially in patients with increased reflex activity. We performed the pendulum test in 15 children with cerebral palsy (CP) and 15 age-matched typically developing (TD) children in two conditions. In the hold condition, the leg was kept isometric in the extended position before release. In the movement condition, the leg was moved up and down before release to reduce the contribution of short-range stiffness. Knee kinematics and muscle activity were recorded. Moving the leg before release increased first swing excursion (p < 0.001) and this increase was larger in children with CP (21°) than in TD children (8°) (p < 0.005). In addition, pre-movement delayed reflex onset by 87 ms (p < 0.05) and reduced reflex activity as assessed through the area under the curve of rectus femoris electromyography (p < 0.05) in children with CP. The movement history dependence of pendulum kinematics and reflex activity supports our hypothesis that muscle short-range stiffness and its interaction with reflex hyper-excitability contribute to joint hyper-resistance in spastic CP. Our results have implications for standardizing movement history in clinical tests of spasticity and for understanding the role of spasticity in functional movements, where movement history differs from movement history in clinical tests.

中文翻译：

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运动史影响痉挛性脑瘫儿童摆锤测试运动学

钟摆测试通过将放松的患者的小腿从水平位置放下并观察肢体运动来评估股四头肌痉挛。第一次摆动偏移 (FS) 随痉挛严重程度的增加而减少。我们最近的模拟研究表明，肌肉短程僵硬及其与反射性过度​​兴奋的相互作用导致初始摆动减少。短程刚度来自肌肉的触变行为，当肌肉保持等长时，拉伸时的纤维刚度会增加。因此，在钟摆测试的第一次摆动期间，纤维刚度可能比连续摆动期间更高。此外，最近有人提出肌梭放电反映的是纤维力而不是速度，因此，反射活动可能取决于纤维刚度。如果这个假设机制是真的，我们希望在腿部移动时观察到更大的第一次摆动幅度和反射性肌肉活动减少，而不是在释放前保持等长，特别是在反射活动增加的患者中。我们在两种情况下对 15 名脑瘫 (CP) 儿童和 15 名年龄匹配的典型发育 (TD) 儿童进行了摆锤测试。在保持状态下，腿在释放前保持在伸展位置等距。在运动状态下，腿在释放前上下移动，以减少短程刚度的贡献。记录膝关节运动学和肌肉活动。在释放前移动腿会增加第一次摆动幅度 (p < 0.001)，而且这种增加在 CP 儿童 (21°) 中比在 TD 儿童 (8°) 中更大 (p < 0.005)。此外，通过股直肌肌电图曲线下面积（p < 0.05）评估患有 CP 的儿童，运动前反射发生延迟 87 毫秒（p < 0.05）并降低反射活动。钟摆运动学和反射活动的运动历史依赖性支持我们的假设，即肌肉短程僵硬及其与反射性超兴奋性的相互作用有助于痉挛性 CP 中的关节超阻力。我们的结果对标准化痉挛临床测试中的运动史以及理解痉挛在功能性运动中的作用具有重要意义，其中运动史与临床试验中的运动史不同。钟摆运动学和反射活动的运动历史依赖性支持我们的假设，即肌肉短程僵硬及其与反射性超兴奋性的相互作用有助于痉挛性 CP 中的关节超阻力。我们的结果对标准化痉挛临床测试中的运动史以及理解痉挛在功能性运动中的作用具有重要意义，其中运动史与临床试验中的运动史不同。钟摆运动学和反射活动的运动历史依赖性支持我们的假设，即肌肉短程僵硬及其与反射性超兴奋性的相互作用有助于痉挛性 CP 中的关节超阻力。我们的结果对标准化痉挛临床测试中的运动史以及理解痉挛在功能性运动中的作用具有重要意义，其中运动史与临床试验中的运动史不同。