Four pairs of muscles arranged symmetrically form the abdominal muscles.These are:
- the large oblique,
- the small oblique,
- transverse rectus
- rectus abdominis.
The rectus abdominis
The rectus abdominis is shaped like a ribbon.This muscle is formed by two bands embedded in the aponeurosis of the three abdominal flat muscles.The aponeurosis is the fibrous membrane of collagen which envelops a muscle.
In a fairly muscular individual, there are at least three intersections of the rectus abdominis:
- below on the pubis;
- above on the sternum;
- the cartilages of the 5th, 6th and 7th ribs.
When the hip is immobile, the rectus abdominis acts as a flexor muscle.Specifically, it allows you to pull your torso towards your pelvis (a movement similar to the crunch or the chest press).
Conversely, when the torso is stationary, the rectus abdominis helps to flex the hips towards the rib cage.It stretches when you carry your chest forward or when you bend your lower back.
The oblique major muscle
Of the three abdominal muscles (large oblique, small oblique and transverse), the large oblique is undoubtedly the most noticeable.This high visibility is mainly due to its shape and size.Indeed, this muscle is palpable in the abdomen, especially in bodybuilders.
As far as the termination is concerned, the muscle fibres of the oblique develop into tendon fibres at the front.They then attach to the centre to form the linea alba and to the anterior half of the iliac bone.
The greater oblique muscle has several functions.For example, when your hips come to rest, it allows your chest to flex towards the hip.On the other hand, when the chest is still, it turns the front part of the pelvis towards the chest.These movements are similar to the chest raise, crunch and reverse crunch respectively.
When contracted, the left and/or right greater oblique allows either lateral flexion or rotation of the torso to the opposite side (chest rise or crunch with rotation).
The small oblique
Don't be surprised if the small oblique doesn't appear in any position.The reason is that it is camouflaged by the large oblique.Its fibres are at an angle to those of the greater oblique and connect back to the lumbar fascia and the anterior part of the hip.
In the anterior part, the lesser oblique muscle inserts into three well-defined areas:
- the last three ribs,
- the white line,
- the anterior part of the iliac bone.
As with the greater oblique, there is the left and right lesser oblique.Both are responsible for bending the torso forward towards the hips and vice versa (bending the hips towards the torso).When they contract on one side only, they promote lateral flexion of the torso.
The Transverse Muscle
Distinguished by its horizontal fibres, the transverse muscle is wrapped under the rectus and obliques.It forms a webbing that fuses the lumbar vertebrae with the white line.It is also found on the iliac crest and the ribs.When it contracts, the ribs contract and you will notice an upward movement of the ribs.
On the other hand, during abdominal breathing, it stretches completely.In fact, the diaphragm tumbles over the viscera and then presses on them to straighten the ribs so that they are spread apart.
When the transverse muscle contracts, there are three movements:
- the descent of the ribs,
- the belly is pulled in,
- the expiration of air from the lung.
A prolonged and complete exhalation allows to work efficiently the transverse muscle.
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