Abstract
The purpose of this study was to clarify the changes in activities of trunk and hip extensor muscles, in the forward bending posture, while in continuous isometric pulling up. Nine healthy male volunteers (mean age, 22.6 years; range, 19-29 years) participated in this study. Surface electromyography was recorded during the contractions of erector spinae of L3 (L3 ES), erector spinae of L5 (L5 ES), rectus abdominus (RA), abdominal oblique (AO), latissimus dorsi (LD), and biceps femoris (BF) muscles. The task was to maintain the pulling up force at 60% of maximal voluntary exertion for 60 seconds in the 30° forward inclination of the trunk relative to a vertical line. The values of median power frequency and average electromyographic activity during the task were calculated. The results showed that the median power frequency of L3 ES, L5 ES and LD significantly decreased at the end of the task compared with its beginning. The average electromyographic activities of RA, AO, LD and GM significantly increased. These results suggest that ES and LD fatigue early and the contractions of RA, AO, LD and GM increase in order to maintain pulling up force while continuous isometric pulling up in the forward bending posture.
