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

本研究集中在五个点来研究三头肌表面肌肉的交替活动；(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)交替肌肉活动时肌电图模式的特征；(4)协同肌肉交替活动时单个运动单元的活动；(5)交替活动在静态肌肉工作中的意义。腓肠肌（MG、LG）和比目鱼肌（SOL）肌肌电-角关系分别呈正反比关系。SOL中力与肌电呈准线性关系，MG与LG呈曲线关系。研究发现，在相对低水平的负荷下（10%最大自主收缩），踝关节角110度处的长时间等距收缩会导致频繁发生肌肉交替活动。此外，定量分析显示，在协同三肌的交替活动中，肌电图不仅在时间上重叠，而且在大小上重叠。另一方面，在重叠期，单个运动单元在招募和招募期间的激活模式没有滞后。因此，在募集期间突触输入a-运动神经元的反向模式不会适用于募集期间的模式。最后，建议协同肌的交替活动类型可以减少肌肉疲劳的发展，并保持第二天肌肉耐力和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.