The rectus abdominis muscle is located in the front of the body, beginning at the pubic bone and ending at the sternum. It is located inside the abdominal region.

The muscle is activated while doing crunches because it pulls the ribs and the pelvis in and curves the back. The muscles are also used when a child is delivered, during bowel movements, and coughing. Breathing in and holding the rectus abdominis in pulls in the abdomen.

When this muscle is exercised and layers of fat disappear from the abdomen, the exposed rectus abdominis muscle creates the look of a “six pack.” Strengthening the muscle also improves performance in sports that require jumping.

The three muscles of the lateral abdominal wall — the internal oblique, the external oblique, and the transverse abdominis  — have fibrous connections that create the rectus sheath, which crosses over and under the rectus abdominis. When doctors perform ultrasound-guided techniques on patients (such as a liver biopsy), they sometimes start scanning at the rectus abdominis muscle to distinguish between the internal oblique, transverses abdominis, and the peritoneal cavity.