RECTUS ABDOMINIS
This is your “6-pack” muscle. This muscle is essential for maintaining good posture and is primarily responsible for flexing the lumbar spine. It also helps to regulate your breathing and plays a vital role in protecting your internal organs by creating intra-abdominal pressure. The muscle group can be worked in 2 different ways – bringing the chest to the pelvis (as in a “crunch”) or by bringing the pelvis towards the chest (as in a leg raise).
EXTERNAL OBLIQUES
These are the largest of your abdominal muscles. They allow your torso to twist as well as supporting your overall posture, pulling your chest down, and like the rectus abdominis, they help protect your vital organs.
INTERNAL OBLIQUES
These control the twisting and turning movement of the torso on the same side of your body. i.e., when you twist to the right, your right internal oblique and left external oblique both contract at the same time.
TRANSVERSE ABDOMINIS
This is your deepest set of abdominal muscles. It is integral to holding your whole abdominal structure together.