In this post, I will discuss about the 'CORE', one of the most popular muscle group in the body. In almost every fitness field, gym, yoga class and even bootcamp session, the so called 'abs section' or CORE is well known to most people who train in gyms and read fitness magazines. Many people have regard the CORE as abdominal muscles, and the minority fitness professionals would know better that the CORE, is much more then just 'abs muscles'. I will discuss a few areas of the mid section and areas of the CORE musculature, this post covers rectus abdominis, internal and external obliques as well as transverse abdominis. The ones who has more interest in building a stronger mid section and so called '6 pack abs', you may find the following illustrations beneficial to you in some way.
Let's start off with rectus abdominis.
RECTUS ABDOMINIS
Origin: Pubic crest and symphysis.
Insertion: Costal cartilages of the fifth through seventh ribs and xiphoid process of the sternum.
Direction of Fibers: Vertical.
Action: Flexes the vertebral column by approximating the thorax and pelvis anteriorly. With the pelvis fixed,
the thorax will move toward the pelvis; with the thorax fixed, the pelvis will move toward the thorax.
Nerve: T5, 6, T7-11, T12, ventral rami.
Weakness: Weakness of this muscle results in decreased ability to flex the vertebral column. In the supine position, the ability to tilt the pelvis posteriorly or approximate the thorax toward the pelvis is decreased, making it difficult to raise the head and upper trunk. For anterior neck flexors to raise the head from a supine position, the anterior abdominal muscles (particularly the rectus abdominis) must fix the thorax. With marked weakness of the abdominal muscles, an individual may not be able to raise the head even though the neck flexors are strong. In the erect position, weakness of this muscle permits an anterior pelvic tilt and a lordotic posture (e.g increased anterior convexity of the lumbar spine).
TRANSVERSE ABDOMINIS
What are the functions of upper and lower abdominals muscles?
The terms upper and lower differentiate two important strength tests for the abdominal muscles. More often than not, there is a difference between the grades of strength attributed to the upper abdominals compared to
those attributed to the lower abdominals. If the same muscles entered into both tests and the difference in strength resulted from a difference in the difficulty of the tests, there should be a fairly constant ratio between the two measurements. In order of frequency, the following combinations of strength and weakness are found:
1. Upper strong and lower weak.
2. Upper and lower both weak.
3. Upper and lower both strong.
4. Lower strong and upper weak.
The difference in strength may be remarkable. A subject who can perform as many as 50 or more curledtrunk sit-ups may grade less than fair on the leg-lowering test. This same subject can increase the strength of the lower abdominals to normal by doing exercises specifically localized to the external oblique. Because the oblique abdominal muscles are essentially fan-shaped, one part of a muscle may function in a somewhat different role than another part of the same muscle. Knowledge of the attachments and the line of pull of the fibers, along with clinical observations of patients with marked weakness and those with good strength, leads to conclusions regarding the action of muscles or segments of abdominal muscles. The rectus abdominis enters into both tests. There is a distinct difference, however, between action of the internal oblique and that of the external oblique as exhibited by the two tests.
When analyzing which muscles or parts of muscles enter into the various tests, it is necessary to observe the movements that take place and the line of pull of the muscles that enter into the movement. As trunk flexion is initiated by slowly raising the head and shoulders from a supine position, the chest is depressed, and the thorax is pulled toward the pelvis. Simultaneously, the pelvis tilts posteriorly. These movements obviously result from action of the rectus abdominis muscle. Along with depression of the chest, the ribs flare outward, and the infrasternal angle is increased. These movements are compatible with the action of the internal oblique.
No test movement can cause an approximation of parts to which the lower transverse fibers of the internal oblique are attached, because these fibers extend across the lower abdomen from ilium to ilium like the lower
fibers of the transversus abdominis. In posterior pelvic tilt and in trunk-raising movements, however, this pan of the internal oblique will act with the transversus to compress the lower abdomen.
Stay tuned for the final part of this abdominal muscles' post.
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| Rectus Abdominis |
EXTERNAL OBLIQUE, anterior fibers
Origin: External surfaces of ribs five through eight interdigitating with the serratus anterior.
Insertion: Into a broad, flat aponeurosis, terminating in the linea alba, which is a tendinous raphe that extends from the xiphoid.
Direction of Fibers: Obliquely downward and medially, with the uppermost fibers more medial.
Action: Acting bilaterally, the anterior fibers flex the vertebral column (approximating the thorax and pelvis anteriorly), support and compress the abdominal viscera, depress the thorax and assist in respiration. Acting unilaterally with the anterior fibers of the internal oblique on the opposite side, the anterior fibers of the external oblique rotate the vertebral column, bringing the thorax forward (when the pelvis is fixed), or the pelvis backward (when the thorax is fixed). For example, with the pelvis fixed, the right external oblique rotates the thorax counter-clockwise, and the left external oblique rotates the thorax clockwise.
Nerves to anterior and lateral fibers: (T5, 6), T7-11, T-12
EXTERNAL OBLIQUE, lateral fibers
Origin: External surface of the ninth rib, interdigitating with the serratus anterior; and external surfaces of the 10th through 12th ribs, interdigitating with the latissimus dorsi.
Insertion: As the inguinal ligament, into the anterosuperior spine and pubic tubercle and into the external up of the anterior 'h of the iliac crest.
Direction of Fibers: Fibers extend obliquely downward and medially, but more downward than the anterior fibers.
Action: Acting bilaterally, the lateral fibers of the external oblique flex the vertebral column with a major influence on the lumbar spine, tilting the pelvis posteriorly. Acting unilaterally with the lateral fibers of the internal oblique on the same side, these fibers of the external oblique laterally flex the vertebral column, approximating the thorax and iliac crest. These external oblique fibers also act with the internal oblique on the opposite side to rotate the vertebral column. The external oblique, in its action on the thorax, is comparable to the sternocleidomastoid in its action on the head.
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| External Obliques |
INTERNAL OBLIQUE (lower anterior)
Origin: Lateral 2h of inguinal ligament and short attachment on iliac crest near the anterosuperior spine.
Insertion: With the transverse abdominis into crest of the pubis, medial part of the pectineal line and into the linea alba by means of an aponeurosis.
Direction of Fibers: Transversely across the lower abdomen.
Action: The lower anterior fibers compress and support the lower abdominal viscera in conjunction with the transversus abdominis.
INTERNAL OBLIQUE (upper anterior)
Origin: Anterior 1/3 of intermediate line of the iliac crest
Insertion: Linea alba by means of an aponeurosis.
Direction of Fibers: Obliquely medially and upward.
Action: Acting bilaterally, the upper anterior fibers flex the vertebral column (approximating the thorax and pelvis anteriorly), support and compress the abdominal viscera, depress the thorax and assist in respiration. Acting unilaterally in conjunction with the anterior fibers of the external oblique on the opposite side, the upper anterior fibers of the internal oblique rotate the vertebral column, bringing the thorax backward (when the pelvis is fixed), or the pelvis forward (when the thorax is fixed). For example, the right internal oblique rotates the thorax clockwise, and the left internal oblique rotates the thorax counterclockwise on a fixed pelvis.
INTERNAL OBLIQUE (lateral fibers)
Origin: Middle xh of intermediate line of the iliac crest and the thoracolumbar fascia.
Insertion: Inferior borders of the 10th through 12th ribs and the linea alba by means of an aponeurosis.
Direction of Fibers: Obliquely upward and medially, but more upward than the anterior fibers.
Action: Acting bilaterally, the lateral fibers flex the vertebral column (approximating the thorax and pelvis anteriorly) and depress the thorax. Acting unilaterally with the lateral fibers of the external oblique on the same side, these fibers of the internal oblique laterally flex the vertebral column, approximating the thorax and pelvis. These fibers also act with the external oblique on the opposite side to rotate the vertebral column.
Nerves to Anterior and Lateral Fibers: T7, 8,19-11 LI, iliohypogastric and ilioinguinal, ventral rami.
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| Internal Obliques |
TRANSVERSE ABDOMINIS
Origin: Inner surfaces of cartilages of the lower six ribs, interdigitating with the diaphragm; thoracolumbar fascia; anterior 3 /4 of internal lip of the iliac crest.
Insertion: Linea alba by means of a broad aponeurosis, pubic crest, and pecten pubis.
Direction of Fibers: Transverse (horizontal).
Action: Acts likes a girdle to flatten the abdominal wall and compress the abdominal viscera; upper portion helps to decrease the infrastemal angle of the ribs, as in expiration. This muscle has no action in lateral trunk flexion, except that it acts to compress the viscera and to stabilize the linea alba, permitting better action by the anterolateral trunk muscles.
Nerve: T7-12, LI iliohypogastric and ilioinguinal, ventral divisions.
Weakness: Permits a bulging of the anterior abdominal wall, which indirectly tends to increase lordosis. During flexion in the supine position and hyperextension of the trunk in the prone position, a lateral bulge tends to occur if the transversus abdominis is weak.
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| Transverse Abdominis |
The terms upper and lower differentiate two important strength tests for the abdominal muscles. More often than not, there is a difference between the grades of strength attributed to the upper abdominals compared to
those attributed to the lower abdominals. If the same muscles entered into both tests and the difference in strength resulted from a difference in the difficulty of the tests, there should be a fairly constant ratio between the two measurements. In order of frequency, the following combinations of strength and weakness are found:
1. Upper strong and lower weak.
2. Upper and lower both weak.
3. Upper and lower both strong.
4. Lower strong and upper weak.
The difference in strength may be remarkable. A subject who can perform as many as 50 or more curledtrunk sit-ups may grade less than fair on the leg-lowering test. This same subject can increase the strength of the lower abdominals to normal by doing exercises specifically localized to the external oblique. Because the oblique abdominal muscles are essentially fan-shaped, one part of a muscle may function in a somewhat different role than another part of the same muscle. Knowledge of the attachments and the line of pull of the fibers, along with clinical observations of patients with marked weakness and those with good strength, leads to conclusions regarding the action of muscles or segments of abdominal muscles. The rectus abdominis enters into both tests. There is a distinct difference, however, between action of the internal oblique and that of the external oblique as exhibited by the two tests.
When analyzing which muscles or parts of muscles enter into the various tests, it is necessary to observe the movements that take place and the line of pull of the muscles that enter into the movement. As trunk flexion is initiated by slowly raising the head and shoulders from a supine position, the chest is depressed, and the thorax is pulled toward the pelvis. Simultaneously, the pelvis tilts posteriorly. These movements obviously result from action of the rectus abdominis muscle. Along with depression of the chest, the ribs flare outward, and the infrasternal angle is increased. These movements are compatible with the action of the internal oblique.
No test movement can cause an approximation of parts to which the lower transverse fibers of the internal oblique are attached, because these fibers extend across the lower abdomen from ilium to ilium like the lower
fibers of the transversus abdominis. In posterior pelvic tilt and in trunk-raising movements, however, this pan of the internal oblique will act with the transversus to compress the lower abdomen.
Stay tuned for the final part of this abdominal muscles' post.
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