Influence of Sitting Posture on Thicknesses and Activities of the Lateral Abdominal Muscles

Abstract

[Purpose] We investigated the changes due to posture in activities of the lateral abdominal muscles by ultra-sound sonography and electromyography. [Subjects] The subjects were 9 healthy adults. [Method] After measuring the muscle thicknesses and activities in quiet breathing and maximum expiration in the supine position, we measured them again in 6 sitting positions: with the trunk upright (U), forward (F)-and backward (B)-tilted with both the spine curved (C) and extended (E). [Results] At maximum expiration, electomyograms showed significant differences only for the internal oblique muscles between UE and FC, UC and BC. In quiet breathing, we found significant differences in muscle thickness of the internal oblique muscles between UE and FC, FE and BC. [Conclusion] We consider that upright sitting with the trunk extended is a posture in which the internal oblique muscles are not active in postural maintenance. From the electromyograms at maximum expiration, we consider this posture is one in which it is easy to show the function of the internal oblique muscles as respiratory muscles.