During human walking, a sudden trip may elicit a Ia afferent fibre mediated short latency stretch reflex. The aim of this study was to investigate soleus (SOL) muscle mechanical behaviour in response to dorsiflexion perturbations, and to relate this behaviour to short latency stretch reflex responses. Twelve healthy subjects walked on a treadmill with the left leg attached to an actuator capable of rapidly dorsiflexing the ankle joint. Ultrasound was used to measure fascicle lengths in SOL during walking, and surface electromyography (EMG) was used to record muscle activation. Dorsiflexion perturbations of 6 deg were applied during mid-stance at walking speeds of 3, 4 and 5 km h−1. At each walking speed, perturbations were delivered at three different velocities (slow: ∼170 deg s−1, mid: ∼230 deg s−1, fast: ∼280 deg s−1). At 5 km h−1, fascicle stretch amplitude was 34–40% smaller and fascicle stretch velocity 22–28% slower than at 3 km h−1 in response to a constant amplitude perturbation, whilst stretch reflex amplitudes were unchanged. Changes in fascicle stretch parameters can be attributed to an increase in muscle stiffness at faster walking speeds. As stretch velocity is a potent stimulus to muscle spindles, a decrease in the velocity of fascicle stretch at faster walking speeds would be expected to decrease spindle afferent feedback and thus stretch reflex amplitudes, which did not occur. It is therefore postulated that other mechanisms, such as altered fusimotor drive, reduced pre-synaptic inhibition and/or increased descending excitatory input, acted to maintain motoneurone output as walking speed increased, preventing a decrease in short latency reflex amplitudes.
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机译:在人的行走过程中,突然的旅行可能会引发Ia传入纤维介导的短潜伏期拉伸反射。这项研究的目的是调查比目鱼(SOL)的肌肉机械行为对背屈摄动的反应,并将这种行为与短时延拉伸反射反应相关联。十二名健康受试者在跑步机上行走,左腿连接到能够快速背屈踝关节的执行器上。超声波用于测量步行过程中SOL中的束长度,而表面肌电图(EMG)用于记录肌肉激活。在站立时以3、4和5 km h -1 sup>的步行速度施加6度背屈摄动。在每种步行速度下,扰动都以三种不同的速度传递(慢:〜170度s -1 sup>,中:〜230度s -1 sup>,快:〜280度s -1 sup>)。在5 km h -1 sup>时,响应于3 km h -1 sup>,束拉伸幅度减小了34–40%,而在3 km h -1 sup>时束拉伸速度慢了22–28%。振幅恒定不变,而伸展反射振幅不变。束拉伸参数的变化可归因于在更快的步行速度下肌肉僵硬度的增加。由于拉伸速度是对肌肉纺锤体的有力刺激,因此可以预期,以更快的步行速度进行的束拉伸速度的降低会降低纺锤体的传入反馈,从而降低拉伸反射幅度,而这不会发生。因此,假定其他机制,例如改变的自体运动驱动,减少的突触前抑制和/或增加的下降性兴奋性输入,都随着步行速度的增加而保持了运动神经元的输出,从而防止了短时反射幅度的降低。
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