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FUNCTIONAL ANATOMY education The rectus abdominis is the most superficial and anterior of the abdominal muscles. It spans the entire abdomen, joining the inferior portion of the sternum and anterior rib cage and the pubis. The right and left sides are separated by the vertical linea alba, a strong, fibrous band that forms the midline of the abdomen and provides attachment points for all of the abdominal muscles. The fibers of the rectus abdominis are also segmented horizontally: each side is divided into five paired sections by a horizontal line of connective tissue. Segmentation of the rectus abdominis allows for graded movement in the trunk. The sequential contraction of segment pairs creates a rounding effect during trunk flexion. In addition to providing graded flexion, the rectus abdominis muscles act unilaterally to assist in lateral flexion. This function is extremely important for proper gait. The right rectus abdominis fires with its corresponding right erector spinae muscles to stabilize the trunk as weight is shifted onto the right lower extremity. As weight transfers onto the left lower extremity, the left rectus abdominis and erector spinae muscles are activated to stabilize the trunk. The rectus abdominis is also important in maintaining upright posture. It counterbalances the posterior erector spinae muscles, keeping the anterior pelvis fixed superiorly. Weakness in the rectus abdominis allows the anterior portion of the pelvis to tip inferiorly (imagine the pelvis as a bowl of water spilling out the front), creating an anterior pelvic tilt. This exaggerates the spine's natural lumbar lordosis, compressing the posterior structures of the spine. Alternately, hypertonicity or overactivation of the rectus abdominis prompts the anterior pelvis to tilt superiorly. This results in posterior pelvic tilt, reducing the spine's natural lumbar lordosis and compressing the anterior structures of the spine. Either of these postural deviations may lead to improper force distribution in the spine, and associated dysfunction and low-back pain. Rectus Abdominis By Christy Cael 46 m a s s a g e & b o d y w o r k s e p t e m b e r / o c t o b e r 2 0 1 8 RECTUS ABDOMINIS Attachments • Origin: Pubic crest and symphysis • Insertion: Ribs 5–7, costal cartilage, and xiphoid process of sternum Actions • Flexes the vertebral column (bilateral action) • Laterally flexes the vertebral column (unilateral action) Innervation • T5–12 • Ventral rami

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