Abdominal muscles/عضلات البطن/腹肌(Fù jī)

Abdominal muscles are special because they provide postural support. They also play a role  

defining the form (with strength exercise). 

For example,the most superficial abdominal muscle, the rectus abdominus, gives the 6-pack ab effect when it is worked to a high degree of fitness. More structurally, the deeper and closer to the spine the particular abdominal muscle is, the more effect over body posture it will have, and this often contributes significantly to a healthy back.

The 6 Abdominal Muscles:

• transverse abdominal

• the internal obliques

Transversus Abdominis - The Deepest Ab Muscle:
The Internal Oblique Muscles - Strong Effect on Posture:
External Obliques:
Rectus Abdominus:
Spinal Action of the Abs:
The Abs and Breathing:

The six abdominal muscles all affect body posture. The deeper the muscle is located (i.e. the closer to the spine), the more powerful effect it will have, and therefore, the greater capacity it will have for creating and maintaining a healthy spine. From deep to superficial the abdominal muscles are:

The transverse abdominus muscle is the deepest of the 6 ab muscles. It can have a tremendous effect on body posture. You cannot touch this muscle from the outside. It wraps around the torso, creating an effect similar to a back support belt.

abdominal muscle,  any of the muscles of the anterolateral walls of theabdominal cavity, composed of three flat muscular sheets, from without inward: external oblique, internal oblique, and transverse abdominis, supplemented in front on each side of the midline by rectus abdominis.

The first three muscle layers extend between the vertebral column behind, the lower ribs above, and the iliac crest and pubis of the hip bone below. Their fibres all merge toward the midline, where they surround the rectus abdominis in a sheath before they meet the fibres from the opposite side at the linea alba. Strength is developed in these rather thin walls by the crisscrossing of fibres. Thus, the fibres of the external oblique are directed downward and forward, those of the internal oblique upward and forward, and those of the transverse horizontally forward.

Around the rectus abdominis, which extends from the pubis upward to the ribs, the above muscles are all fibrous. In the region of the groin, between the pubic bone and the anterior superior iliac spine, a specialized arrangement of these fibres permits the formation of the inguinal canal, a passage through the muscular layers. This develops at birth as the testes descend out of the abdominal cavity through its wall into the scrotum. In the female this is replaced by a fibrous cord from the uterus. This gap is a potentially weak area where inguinal hernias can occur.

The muscles of the abdominal walls perform a variety of functions: They provide a tonic, elastic muscular support for the viscera and, by their recoil, pull down the rib cage in expiration. They contract against blows to form a rigid protective wall for the viscera.  When the glottis is closed and the thorax and pelvis are fixed, these muscles take part in the expulsive efforts of urination, defecation, childbirth, vomiting, and of singing and coughing.  When the pelvis is fixed, they initiate the movement of bending the trunk forward. Thereafter, gravity comes into play, the abdominal muscles relax, and the muscles of the back then take on the strain.  Conversely, the abdominal muscles come into play in preventing hyperextension.  When the thorax is fixed, the abdominal muscles can pull up the pelvis and lower limbs. The muscles of one side can bend the vertebral column sideways and assist in its rotation.

The internal obliques are a pair of ab muscles, residing on each side of the torso. They are the next deepest, after the transversus. Just like the transversus, they affect body posture tremendously, only slightly less, because of their more superficial position. The internal obliques are involved in, among other things, rotation and lateral flexion of the spine.

The external obliques are another pair of ab muscles that are located on either side of the torso. The external obliques are more superficial than the transversus and the internal obliques. Consequently the external obliques have less effect (but certainly not none) on body posture. Like the internal obliques, the external obliques are involved in, among other things, rotation and lateral flexion of the spine.

The rectus abdominus muscle is the most superficial of the abdominal muscles. It and the external obliques affect body posture, just not as much as the deeper interal obliques and transversus. The rectus abdominis muscle is responsible for the 6-pack ab look in very fit people.

Because muscles work in groups, we call the abdominal muscles spinal flexors. Their main job is to bend the spine forward, when contracting coencentrically. The back muscles counterbalance the action of the abs, and are called spinal extensors. What this means is that when the abdominals shorten to flex the spine, the back muscles are put on a stretch, and vice versa.

The abdominals participate in the breathing process, especially during exhale, when they help force air out of the lungs by depressing the thorax.