Human muscle stretch reflexes: the effects of stimulus properties, muscle state and subject intention

最著名的肌肉反射是肌腱痉挛，通常是用小锤子敲击肌腱引起的。这种敲击会对肌肉施加非常迅速的拉伸，从而产生拉伸反射。然而，可以观察到不同的拉伸反应，以减缓或快速拉伸，或对肌肉的振动。正常情况下，当放松的人的肌肉伸展时，不会观察到积极的反应。然而，当人从事一项任务并收缩肌肉时，拉伸调节肌肉活动，使肌肉收缩的增加与拉伸相反，并保护关节的位置不受外部干扰。这就是伸展反射发挥作用的日常情况。尽管一百多年来进行了广泛的研究，但对于拉伸反射的行为以及它们在运动控制中的作用，研究人员仍然没有达成共识。甚至连反射与自愿肌肉活动的界限也不总是确定的。伸展反射的显著特征之一是其行为的变异性，这取决于所涉及的特定肌肉、其收缩程度、伸展类型和人所从事的任务。这种可变性使研究人员很难确定反射在运动控制中的作用。为了研究受试者的拉伸反射行为，我们将测量不同条件下肘部肌肉的电活动、肘部位置和关节产生的力。一系列五个实验将调查特定的悬而未决的问题，例如受试者的意图对肌肉活动调节的影响，以及肌肉活动调节的改变如何改变我们四肢的僵硬。这一系列实验的目的是填补拉伸反射行为图像中的重要空白。

The best known muscle reflex is the tendon jerk, which is usually evoked by tapping the muscle tendon with a small hammer. This tap imposes a very rapid stretch on the muscle, which produces a stretch reflex. Different stretch responses, however, can be observed to slow or fast stretches, or to vibration of muscle. Normally, when the muscles of a relaxed person are stretched, no active response is observed. However, when the person is engaged in a task and contracting their muscles, then stretch modulates the muscle activity such that an increase in contraction of the muscle opposes the stretch and defends the position of the joint against the external disturbance. This is the everyday situation in which stretch reflexes operate. Despite extensive investigation for over a hundred years, there is still no consensus among researchers about the behaviour of stretch reflexes nor about their role in the control of movement. Even the demarcation of reflex from voluntary muscle activity is not always certain. One of the outstanding features of stretch reflexes is the variability of their behaviour, which depends on the particular muscle involved, its level of contraction, the type of stretch and the task in which the person is engaged. This variability has made it difficult for researchers to determine the role of reflexes in the control of movement. In order to study stretch reflex behaviour in human subjects, we will measure the electrical activity of elbow muscles, the elbow position and the force generated at the joint under a variety of conditions. A series of five experiments will investigate specific unresolved issues such as the effect of subject intention on the modulation of muscle activity and how altered modulation of muscle activity may change the stiffness of our limbs. The objective of the experimental series is to fill in important gaps in the picture of the behaviour of the stretch reflex.