The internal abdominal girdle is a group of four muscles that make up the core or abdomen. They include External Oblique, Internal Oblique, Transversus Abdominis, and Rectus Abdominis. The muscles are important for protecting the internal organs that are contained in the abdominal cavity and organs located in the pelvic cavity. These muscles are also important for stability and allowing your body to move properly. Even though it might not always seem like it, you are using your abdominal muscles a lot, in tasks like standing, walking, and sitting.