The abdominal muscles are a group of stabilizing and flexing muscles located on the anatomical core of the human body. These muscles are composed of six individual muscles, and their function is related to posture, bending the upper body and rotating about the spine. Additionally, these muscles are important in breathing and are often aesthetically desirable. The lower abdominals do not refer to one of the six specific muscles but rather to a portion of the rectus abdominus that gives the "six pack" its famous shape.
The six sub-types of abdominal muscles are comprised of two internal obliques, two external obliques, the rectus abdominus and the transverse abdominal muscles. The internal obliques lay superficial to — above — the transverse abdominal, and with one oblique on each side, aid in the rotation and lateral flexion of the spine. Similarly, the external obliques are symmetrically located on each side of the spine superficial to their internal counterparts and additionally aid in spinal flexion as well as core rotation.
The rectus abdominus, containing the lower abdominals, play the primary role of bending the core forward. These are also the most superficial of the six muscles, so many people who are concerned with aesthetically improving the appearance of their abs tend to focus on this muscle group. People who have high-functioning fitness levels might see a marked improvement in both the size and definition of the lower abdominals. In extreme cases, this might yield a six-pack" look in which segments of the lower abdominals are visible as distinct structures.
The transversus abdominus, or transverse abdominal muscles, are important in supporting the other abdominal muscles and aiding in postural stability. These muscles wrap around the spine in a similar fashion to a support belt and are the anatomically deepest of all the abdominal muscles. Although the muscles of the abdomen each have unique abilities and functions, they importantly overlap in many roles, working together to help the body stay erect and stable throughout a number of activities.
Breathing is an activity necessary for life, and it would not be possible without the assistance of the abdominal muscles. During exhalation, the contraction of the abdomen allows for the contraction of the lungs. This decreases lung volume and actively removes air from the lungs.
Although the lower abdominals play an integral role in everyday functions, they are most recognized because of the coveted "six pack." If a person wants to obtain this chiseled look, their best option would be to exercise. Muscles have the ability to gain shape, size and definition, through repeated strain. To achieve the "six pack," repeated strain should be enforced on the muscles through sit-ups, crunches or other strengthening activities that stress the lower abdominals in a desired manner.