The muscles of the abdomen, lower back, and pelvis are separated from those of the chest by the muscular wall of the diaphragm, the critical breathing muscle. Lying exposed between the protective bones of the superiorly located ribs and the inferiorly located pelvic girdle, the muscles of this region play a critical role in protecting the delicate vital organs within the abdominal cavity. In addition to providing protection, these core muscles also function in movement of the trunk, posture, and stability of the entire body.
Extending across the anterior surface of the body from the superior border of the pelvis to the inferior border of the ribcage are the muscles of the abdominal wall, including the transverse and rectus abdominis and the internal and external obliques. Working as a team, these muscles contract to flex, laterally bend, and rotate the torso. The abdominal muscles also play a major role in the posture and stability to the body and compress the organs of the abdominal cavity during various activities such as breathing and defecation.
The muscles of the lower back, including the erector spinae and quadratus lumborum muscles, contract to extend and laterally bend the vertebral column. These muscles provide posture and stability to the body by holding the vertebral column erect and adjusting the position of the body to maintain balance.
Attached to the pelvis are muscles of the buttocks, the lower back, and the thighs. These muscles, including the gluteus maximus and the hamstrings, extend the thigh at the hip in support of the body’s weight and propulsion. Other pelvic muscles, such as the psoas major and iliacus, serve as flexors of the trunk and thigh at the hip joint and laterally rotate the hip as well.