Abdominal crunches are similar to situps, except you only lift your upper back and shoulders off the floor rather than sitting completely upright. The abdominal muscles that perform the abdominal crunch are the rectus abdominus, transverses abdominus, and the obliques. Speak to your doctor before doing abdominal crunches as part of an exercise routine.
Rectus Abdominus
The rectus abdominus is a long muscle that runs the length of the front of your abdomen to form the six pack. It starts at the pubic bone above your crotch and runs upward to attach to the tip of the breast bone and the cartilage attached to the middle three ribs. It flexes your trunk when you bend forward and helps keep pressure on your abdominal organs.
Transversus Abdominus
The transversus abdominus runs laterally, or along your side from your back to your front, between the bottom ribs and your hip bone. Its the deepest of the lateral abdominal muscles. It starts at the bottom of your ribcage, lower back, and hip bone, and runs forward to join the oblique muscles at the linea alba, which is the line of connective tissue at the midline of your abdominal muscles. The transversus abdominus compresses and supports your internal abdominal organs.
Internal Oblique
The internal oblique is the middle lateral abdominal muscle, lying above the transversus abdominus and below the external oblique. The fibers start at the lower back and hip bone and run at an angle up and foreword to attach to the bottom of the ribcage, linea alba and the pubic bone. The internal oblique supports the abdominal organs and flexes and twists your trunk.
External Oblique
The external oblique is the outermost lateral abdominal muscle and the fibers run perpendicular to the internal oblique. It starts at the bottom edges of the rib cage and runs downward to attach to the top of the hip bone and the linea alba. The external oblique supports your abdominal organs, flexes the trunk, and works with the internal oblique to twist your trunk.
