Butler A J, Yue G, Darling W G
Department of Exercise Science, University of Iowa, Iowa City 52242.
Brain Res. 1993 Dec 31;632(1-2):95-104. doi: 10.1016/0006-8993(93)91143-g.
The purpose of this study was to evaluate the effects of the levels of voluntary isometric contraction on the Hoffman reflex in human soleus and medial gastrocnemius (MG) muscles. H-reflexes were recorded in sixteen healthy adults at each of 16 isometric plantarflexion (pf) torque levels ranging from 0-100% of their maximum voluntary isometric contraction (MVC) and were elicited at two intensities of stimulation: (i) supramaximal for M-response and (ii) a submaximal stimulus that produced an H-reflex in soleus that was 50% of maximum H-reflex at rest. The H-reflex peak-to-peak amplitudes were linearly related to pf torque levels ranging from 0 to 50% MVC at both supramaximal and submaximal stimulus intensities. The slope of this relationship was higher for the submaximal stimulation. Beyond 60% of MVC, the soleus H-reflex amplitude showed no further increase with increasing pf torque for both stimulus intensities. Thus, beyond 50-60% of MVC the soleus H-reflex does not provide an accurate measure of soleus motor neuron pool excitability. Further experimental results showed that the H-reflex amplitude at a given torque level depended on whether torque was increasing or decreasing. When torque was increasing, the amplitude of the H-reflex was larger than when the same torque was maintained at a constant level. In contrast, if the torque was decreasing, amplitude of the reflex was lower than when torque was increasing. Therefore, variations in H-reflex amplitudes at a given torque level may be more closely correlated to the direction of the ongoing contraction than to the actual muscle force being produced at the time the H-reflex is elicited.
本研究的目的是评估自主等长收缩水平对人比目鱼肌和腓肠肌内侧（MG）霍夫曼反射的影响。在16名健康成年人中，于16种等长跖屈（pf）扭矩水平下记录H反射，这些扭矩水平范围为其最大自主等长收缩（MVC）的0 - 100%，并在两种刺激强度下引出H反射：（i）对M波为超强刺激，（ii）亚最大刺激，该刺激在比目鱼肌中产生的H反射为静息时最大H反射的50%。在超强和亚最大刺激强度下，H反射峰 - 峰振幅与0至50%MVC的pf扭矩水平呈线性相关。亚最大刺激时这种关系的斜率更高。超过MVC的60%后，对于两种刺激强度，比目鱼肌H反射振幅均未随pf扭矩增加而进一步增大。因此，超过MVC的50 - 60%后，比目鱼肌H反射不能准确测量比目鱼肌运动神经元池的兴奋性。进一步的实验结果表明，在给定扭矩水平下H反射振幅取决于扭矩是增加还是减小。当扭矩增加时，H反射振幅大于将相同扭矩保持在恒定水平时的振幅。相反，如果扭矩减小，反射振幅低于扭矩增加时的振幅。因此，在给定扭矩水平下H反射振幅的变化可能与正在进行的收缩方向的相关性比与引出H反射时实际产生的肌肉力量的相关性更强。
