Moseley G Lorimer, Hodges Paul W, Gandevia S C
Prince of Wales Medical Research Institute, Sydney, Australia.
J Physiol. 2003 Mar 1;547(Pt 2):581-7. doi: 10.1113/jphysiol.2002.024950. Epub 2002 Dec 20.
During voluntary arm movements, the medial back muscles are differentially active. It is not known whether differential activity also occurs when the trunk is perturbed unpredictably, when the earliest responses are initiated by short-latency spinal mechanisms rather than voluntary commands. To assess this, in unpredictable and self-initiated conditions, a weight was dropped into a bucket that was held by the standing subject (n = 7). EMG activity was recorded from the deep (Deep MF), superficial (Sup MF) and lateral (Lat MF) lumbar multifidus, the thoracic erector spinae (ES) and the biceps brachii. With unpredictable perturbations, EMG activity was first noted in the biceps brachii, then the thoracic ES, followed synchronously in the components of the multifidus. During self-initiated perturbations, background EMG in the Deep MF increased two- to threefold, and the latency of the loading response decreased in six out of the seven subjects. In Sup MF and Lat MF, this increase in background EMG was not observed, and the latency of the loading response was increased. Short-latency reflex mechanisms do not cause differential action of the medial back muscles when the trunk is loaded. However, during voluntary tasks the central nervous system exerts a 'tuned response', which involves discrete activity in the deep and superficial components of the medial lumbar muscles in a way that varies according to the biomechanical action of the muscle component.
在自愿性手臂运动过程中，背部内侧肌肉的活动存在差异。尚不清楚当躯干受到不可预测的扰动时，最早的反应由短潜伏期脊髓机制而非自愿指令引发时，是否也会出现这种差异活动。为了评估这一点，在不可预测和自我引发的条件下，将一个重物放入站立受试者（n = 7）手持的桶中。记录了深层（Deep MF）、浅层（Sup MF）和外侧（Lat MF）腰多裂肌、胸段竖脊肌（ES）和肱二头肌的肌电图活动。在不可预测的扰动过程中，肱二头肌首先出现肌电图活动，然后是胸段竖脊肌，随后多裂肌各部分同步出现。在自我引发的扰动过程中，七名受试者中有六名深层腰多裂肌的背景肌电图增加了两到三倍，负荷反应的潜伏期缩短。在浅层腰多裂肌和外侧腰多裂肌中，未观察到背景肌电图的这种增加，负荷反应的潜伏期延长。当躯干负重时，短潜伏期反射机制不会导致背部内侧肌肉的差异作用。然而，在自愿任务期间，中枢神经系统会产生一种“调谐反应”，这涉及到内侧腰部肌肉深层和浅层成分的离散活动，其方式会根据肌肉成分的生物力学作用而有所不同。
