Table_2_Movement History Influences Pendulum Test Kinematics in Children With Spastic Cerebral Palsy.docx

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.

钟摆试验（pendulum test）通过将放松受试者的小腿从水平位置下放并观察肢体运动，来评估股四头肌痉挛（quadriceps spasticity）程度。首次摆动幅度（first swing excursion, FS）随痉挛严重程度升高而降低。我们近期的模拟研究表明，初始摆动幅度降低源于肌肉短程刚度（short-range stiffness）及其与反射亢进的相互作用。短程刚度源于肌肉的触变性行为（thixotropic behavior）：当肌肉保持等长收缩（isometric）时，牵伸后的肌纤维刚度会升高。因此，钟摆试验首次摆动过程中的肌纤维刚度可能高于后续摆动。此外，近期有研究提出，肌梭（muscle spindle）放电反映的是肌纤维张力而非运动速度，因此反射活动可能依赖于肌纤维刚度。若该假说机制成立，我们预期在释放前对小腿进行主动运动而非保持等长收缩时，会观察到更大的首次摆动幅度以及更低的反射性肌肉活动，尤其在反射活动增强的受试者中。本研究纳入15名脑瘫（cerebral palsy, CP）儿童与15名年龄匹配的典型发育（typically developing, TD）儿童，在两种实验条件下开展钟摆试验：静态保持组中，释放前将小腿保持在伸直位的等长收缩状态；主动运动组中，释放前对小腿进行上下往复运动，以削弱短程刚度的影响。研究记录了膝关节运动学数据与肌肉活动信号。结果显示，释放前活动小腿可提升首次摆动幅度（p < 0.001），且脑瘫儿童的幅度提升值（21°）显著高于典型发育儿童（8°，p < 0.005）。此外，在脑瘫儿童中，前置运动使反射起始延迟87 ms（p < 0.05），并通过股直肌肌电图（rectus femoris electromyography）曲线下面积评估的反射活动显著降低（p < 0.05）。钟摆运动学与反射活动对运动史的依赖性，验证了我们的假说：肌肉短程刚度及其与反射亢进的相互作用，是痉挛型脑瘫患者关节过度阻力的成因之一。本研究结果可为痉挛临床评估中运动史的标准化提供参考，也有助于理解痉挛在功能性运动中的作用——此类运动中的运动史与临床评估中的运动史存在显著差异。