The purposes of this study were to investigate the electromyographic (EMG) activities of the abdominal muscles during walking and to clarify abdominal muscle function. Twenty-eight healthy male volunteers (20.8 ± 2.5 years) participated in this study. Bipolar surface electrodes were placed on both sides of the rectus abdominis and the oblique abdominis muscles. The EMG and signals from foot switches during standing and walking were recorded and analyzed. The EMG raw data were rectified and averaged, and then the integrated EMG was normalized by the values obtained during maximum voluntary contractions (%MVC). The rectus abdominis muscles showed continuous activity (1.6% MVC) during walking. The oblique abdominis muscles showed two patterns during walking. One pattern was a continuous pattern (continuous group) and the other had a peak during the swing phase (the peak pattern group). The amount of activity of the oblique abdominis muscles during walking in the continuous pattern group was 10.1% MVC and that in the peak pattern group was 13.2% MVC. These data suggested that the abdominal muscles play almost no role in maintaining the standing posture and that the rectus abdominis muscles show a little continuous activity. This is because the movement of trunk flexion is very small during walking, when a man's center of gravity moves in thehorizontal plane. The oblique abdominis show two patterns. This is because the opposite rotation movement of trunk and pelvis.
