Rectus abdominis Definition
It is a long, flat, paired muscle situated in front of the abdomen. The fibrous tissue falls under the group of abdominal muscle. Normally, rectus abdominis, quadratus lumborum and erector spinae form the three major trunk muscles. It is commonly called “abs” or “6-pack”. “Rectus” refers to the origin of the muscle while “abdominis” relates to the abdomen.
Rectus abdominis Location
This large muscle extends vertically along the entire length of the anterior abdomen on each side. The parallel muscles are separated by a fibrous structure made of collagen connective tissue called linea alba. Normally, this midline band runs from the xiphoid process to the pubic symphysis.
Rectus abdominis Innervation
The thoracoabdominal nerves innervate the abs by perforating the rectus sheath. Repeated external force on the abdomen can exert direct pressure on them and cause nerve entrapment syndrome.
Rectus abdominis Anatomy
The muscle usually extends from the pubic symphysis, pubic crest and pubic tubercle inferiorly, and surpasses the metasternum. Here, it inserts into the 5th, 6th and 7th ribs of the costal cartilages by three unequal portions. For this reason, the 5th rib has some fibers of insertion into the anterior extremity. The costoxiphoid ligaments and the side of the xiphoid process are often attached with some of the fibers of the muscle. The rectus sheath, formed by the aponeuroses of the transversus abdominis and oblique muscles, encloses the flat muscle and holds it in position. However, the sheath does not restrict the movement of the muscle during contractions. Rupture of the epigastric arteries can often lead to accumulation of blood in the sheath, causing rectus hematoma. The muscle is crossed by three bands of connective tissue called the tendinous intersections at the level of the umbilicus.
The abs is typically a Mathes and Nahai Type 3 muscle, comprising of two dominant pedicles, with a rich supply of arterial blood vessels. It is also composed of 53.9% type 2 fibers. On the posterior side of the muscle, the lateral epigastric artery and vein runs superiorly and enters the rectus fascia at the arcuate line to serve its lower portion. On the other hand, the upper part of the muscle is supplied with blood from the superior epigastric artery. Additional amount of blood is usually delivered by the lower six intercostal arteries.
Rectus abdominis Function
The muscle aids in flexing the lumbar region of the vertebral column when performing certain types of abdominal exercises, such as a crunch. In this position, it is possible to draw the breastbone towards the pubis. Most importantly, it facilitates breathing as well as helps in respiration, particularly during forced exhalation after an exercise. However, it is not a muscle of inspiration. The long, paired muscle is capable of stretching the abdominal wall while compressing the abdominal contents. In this way, the organs remain intact when exercising, defecating, lifting heavy objects, or giving birth in females. The other actions of the muscle include:
- Stabilization of the pelvis to permit the lower limb muscles to work properly
- Inflexion of the trunk on the pelvis
- Controlling the tilt of the pelvis during contraction
The vertical rectus muscle flap is often used to fit a tissue defect, particularly in the head, neck and face. It has also played a prime role in a large number of successful hernia repairs/surgeries
Rectus abdominis Damage
Excessive strain on the abs during a heavy workout can result in tiny tears. In a variety of sports, athletes can sustain injury in the muscles of the abdomen, causing an abdominal muscle strain/pulled abdominal muscle. Depending on the severity of the injury, the muscle fibers are either torn or ruptured. Severe pain and inflammation of the abdominal muscle at the point of attachment on the pubic bone is a common symptom of the condition. There could also be a sensation of tightness or cramp/spasm when the muscles are stretched or contracted.
Some individuals may suffer from desmoids tumors, also known as “aggressive fibromatosis”, in the right rectus muscle. These abnormal masses are clearly evident on a CT or MRI scan image. A rare disorder of the abs, known as diastasis rectus abdominis (DRA), can cause separation of the muscle into right and left halves. As the symptoms of this ailment resemble epigastric hernia or incisional hernia, an ultrasound must be conducted to rule out the latter. However, in spigelian hernia, the rectus muscle and spigelian fascia are affected. A tear in the abdominal wall can also cause hernia, marked by abnormal protrusion of the intestines or connective tissue through the rectus muscle. Treatment of DRA is aimed at supporting both the organs and joints for a better outcome. This could be achieved by using a new technique called kinesio taping, in which an elastic tape with a fine texture is wound around the abdomen to stimulate the weak muscle and mitigate the pain. Women with multiple pregnancies have a greater chance of suffering from this condition. There have been some medical reports addressing the possibility of endometriosis of the rectus muscle. In some cases, the muscle may also undergo dystrophy and atrophy. In rare cases, rectus muscle knots may develop either due to injury or overuse, resulting in pain and weakness. Use of manual muscle testing helps physicians to evaluate the function and strength of the muscle in order to modify its various activation patterns. Strength examination comprises of certain measuring devices such as hand-grip, fixed, and isokinetic dynamometry that are used to release the muscle pain.
Rectus abdominis Pictures
Rectus abdominis muscle in Animals
The muscle is present in most vertebrates, including frog, dog, cattle and cat, and performs similar functions. However, anatomically, the number of tendinous intersections in the abs of animals is slightly different from humans.