2012 年 12 巻 p. 29-34
The aim of this study was to clarify the function of the abdominal muscles in stabilizing the trunk during shoulder flexion. We used surface electromyographic (EMG) data from the rectus abdominis (RA) and external oblique abdominis (EO) muscles of 7 healthy male subjects (age 29.4 ± 4.7 years). Muscle activities of the right anterior deltoid, serratus anterior (SA), RA, and EO muscles were recorded while maintaining right shoulder flexion. The subjects held a plumb-bob of 5% of body weight. The angles of shoulder flexion were 30°, 60°, 90°, and 120°, and they were maintained for a full 5 s in each position. EMG activities of EO during shoulder flexion of 120° and 90° were significantly greater than that during shoulder flexion of 30° (p<0.05). EMG activity of SA during shoulder flexion of 120° was significantly greater than that during shoulder flexion of 30° (p<0.05). EMG activity of RA during shoulder flexion of 120° was significantly higher than those during shoulder flexion of 30° and 60° (p<0.05). The abdominal muscles are necessary to stabilize rotation of the trunk when the scapula is moved and rotated upward by concentric contraction of SA. Therefore, EO on the side of movement plays a major role in controlling trunk rotation toward the contralateral side. Although the activity level of RA was low, we consider that the finding that this muscle showed significantly greater EMG activity was due to its activity in efficiently fixing the rectus sheath while acting in concert with EO. In physical therapy evaluating motor function of the upper extremities, it is important to evaluate the abdominal muscles as well.