Motor unit activation patterns during the alternate activity in the synergistic muscles

本研究从五个方面探讨小腿三头肌的交替活动;（1）控制交替肌肉活动的出现，（2）关节角度、力输出和肌电图（EMG）活动之间的功能相互关系，（3）交替肌肉活动期间EMG模式的特征，（4）协同肌肉交替活动时单个运动单位的活动;（5）静态肌肉工作时交替活动的意义。LG）和比目鱼肌（SOL）。SOL的力与肌电呈准线性关系，MG和LG呈曲线关系。结果发现，在相对较低的负荷水平（10%最大随意收缩）下，踝关节角为110 °的长时间等长收缩导致频繁发生交替肌肉活动。定量分析表明，在协同的三块肌肉交替活动过程中，肌电不仅在时间上存在重叠，而且在幅度上也存在重叠。另一方面，在重叠期，在招募和去招募期间，单个运动单位的激活模式没有滞后。因此，在募集过程中突触输入到α-运动神经元的反向模式将不适用于去募集过程中的突触输入。最后，提示协同肌肉的交替活动类型减少了肌肉疲劳的发展，并保持了肌肉耐力和次日最大力量输出的功能能力。

This study has focused on five points to investigate the alternate activity in the triceps surae muscles ;(1) controlling the emergence of alternate muscular activity, (2) functional interrelationships between joint angle, force output and electromyographic (EMG) activity, (3) characteristics of EMG patterns during alternate muscular activity, (4) single motor unit activity during alternate activity in the synergistic muscles and (5) significance of alternate activity in the static muscle work.EMG-angle relationships showed direct and inverse proportion in gastrocnemius (MG, LG) and soleus (SOL) muscle respectively. There was a quasi-linear relationship between force and EMG in SOL, but MG and LG took on a curvilinear relationship. It was found that prolonged isometric contractions at 110 degrees of ankle joint angle under relatively low level workload (10% maximal voluntary contraction) resulted in the frequent occurrence of alternate muscular activity. Moreover, quantitative analysis revealed the existence of the EMG overlap not only in time but also in magnitude during the alternate activity among synergistic three muscles. In the overlap periods, on the other hands, there is no hysteresis in activation patterns of single motor units during recruitment and derecruitment. Therefore, the reverse pattern of synaptic input to a-motoneurons during recruitment would not be applied to that during derecruitment. Finally, it is suggested that the type of alternate activity in the synergistic muscles reduce the development of muscle fatigue and keep the functional ability for muscle endurance and maximal force output on the next day.