| Abstract: | The activity of the leg and abdominal muscles in trunk flexion and extension was investigated with reference to the sudden decreases and increases of the erectores spinae activity. The movement was performed under conditions with and without an additional load, and with and without fatigue. Surface EMGs were recorded from the erectores spinae, the gluteus maximus, the semitendinosus, the rectus abdominis and the external oblique. The pattern of activity was analysed using EMG stick diagrams. Under the condition without fatigue, the semitendinosus activity increased during the sudden changes of the erectores spinae activity, but the abdominal muscles were not activated during the movement. However, the rectus abdominis was activated whenever the semitendinosus activity did not increase during the changes of the erectores spinae activity. Under the condition of fatigue, the leg muscle was vigorously active during the movement, and the abdominal muscles were activated before and after the erectores spinae activity changed suddenly. The results suggest that the leg muscle plays some important part during the sudden changes of the erectores spinae activity. |
