the rectus abdominis muscle is your “six pack” muscle. It originates on the pubic bone, and inserts on the costal cartilage of ribs 5-7, and the xiphoid process of the sternum.its main actions are to flex and rotate the spine, and to increase intra-abdominal pressure. This muscle is often tight in people who slouch, or have a posteriorly tilted pelvis. In people with an anteriorly rotated pelvis this muscle is often weak and needs to be strengthened. Trigger points in this muscle refer pain into the mid and lower back