A BASIC STUDY OF EXCITABILITY CHANGES IN HUMAN MOROR CORTEX AND MUSCLE FATIGUE

为了明确肌肉疲劳引起的人体运动皮层兴奋性变化的功能和测量方法，本研究首先研究了肌肉收缩任务条件的差异如何改变经颅磁刺激（TMS）引起的MEP和沉默期反应。其次，100%和50%MVC诱导的肌肉疲劳如何通过双tms影响运动皮层的抑制和促进反应，以及疲劳时单MEPs的变化。两种任务条件包括从10到70%MVC的2秒斜坡方法和在20、33、46和60%MVC四个强度下每20秒任务的恒定方法。经颅磁刺激的4个MEP幅值随恒定方法中%MVC的4个强度而增加。但在2秒斜坡法中，相同%MVC强度的MEP振幅减小，而相同%MVC强度的MEP振幅增大。斜坡法测得的MEP下降模式可能与运动皮层和脊髓系统的强度和速度控制有额外的兴奋性作用。采用单试验刺激、单试验+ISI 3ms条件刺激和双经颅磁刺激双试验+ISI 10ms条件刺激的方法来评估人体运动皮层的皮质-皮质抑制和促进反应。三种mep振幅在100% mvc疲劳后比疲劳前下降更多。疲劳后3ms的%MEP下降较多，而10ms的%MEP增加较多。另一方面，在50%的mvc后，MEPs振幅也比之前下降得更多。但ISI 3ms后的%MEP比肌肉疲劳前明显增加。肌肉疲劳后，短mvc组兴奋性只增加促进，长mvc组兴奋性抑制和促进均增加。在l00mvc和50%MVC的收缩过程中，肌肉力量和iEMG逐渐下降，沉默期随着疲劳而缩短。在100%MVC模式下，MEP振幅保持不变，而在50%MVC模式下，MEP振幅保持不变或逐渐增加。

To define the function and measurement of excitability change in human motor cortex due to muscle fatigue, this propose was firstly to examine how differences in task conditions of muscle contraction change MEP and silent period responses elicited by transcraninal magnetic stimulation (TMS). Secondly how muscle fatigue induced by 100%MVC and 50%MVC influences the inhibitory and facilitatory responses in motor cortex by double TMSs and how single MEPs change during fatigue.Two tasks conditions consist of 2-sec ramp method from 10 to 70%MVC and constant method for each 20 seconds task at four intensities of 20, 33, 46 and 60%MVC. Four MEP amplitudes by TMS increased according to four intensities of %MVC in constant method. But MEP amplitudes decreased while same %MVC intensities increased in 2-sec ramp method. The decline pattern of MEP by ramp method is suggested to have the function of additional excitability to the strength and speed controls in motor cortex and spinal system.The method of only test stimulus, test+ISI 3ms conditioning stimuli and test +ISI 10 ms conditioning stimuli by double TMS is indicated to estimate the cortico-cortical inhibitory and facilitator responses in human motor cortex. Three MEPs amplitudes decreased more after than before muscle fatigue of l00%MVC. %MEP of 3ms decreased more but % MEP of l0ms increased more after than before fatigue. On the other hand, MEPs amplitudes also decreased more after than before 50%MVC. But %MEP of ISI 3ms increased more after than before muscle fatigue. After muscle fatigue the excitability increased only facilitation in Short l00%MVC but increased both inhibition and facilitation in long 50%MVC. During contraction in l00%MVC and 50%MVC, muscle strength and iEMG gradually decreased and Silent Period shortened with fatigue in both %MVC. MEP amplitude kept constant in 100%MVC but kept constant or progressively increased in 50%MVC.