The rectus abdominis muscle is one of the anterior abdominal wall muscles, which together act to keep the viscera in place. Contraction aids expiration as well as evacuation of the rectum, bladder and uterus. It is a sheet-like muscle that is supplied by the ventral rami of the lower six or seven thoracic nerves. Normally the muscle contracts as one, with no independent control of the upper vs. the lower, or left vs. right, parts of the muscle. This is evident by the fact that the umbilicus remains in a central position during contraction. This is most easily demonstrated by having the subject lie supine, and then raise their head from the couch, or attempt a sit-up. Beevor’s sign describes the upward movement of the umbilicus when performing either of these manoeuvres due to weakness of the lower part of the rectus abdominis (see Fig. 1). Or, less
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