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From ancient times to the present: How did the human rectus abdominis muscle evolve?
The rectus abdominis, a term derived from Latin, means "straight abdominal muscle", and is a pair of segmented skeletal muscles located directly in front of the abdomen. The two muscles are separated by a band of dense connective tissue called the linea alba, while its lateral edges are defined by the linesa lunulae. The rectus abdominis extends from the pubic symphysis, pubic crest, and pubic tubercle to the xiphoid process and costal cartilages of the 5th to 7th ribs. This muscle is contained within the rectus abdominis fascia, which is composed of the aponeurosis of the lateral abdominal muscles. It is important to note that the rectus abdominis has multiple intersections of connective tissue bands called tendinous junctions that divide it into different muscle bellies.
These muscle bellies are usually clearly visible in individuals with low body fat content and can be divided into anywhere from two to as many as twelve muscle groups, depending on the individual, although six is the most common.
Composition of the rectus abdominis muscle
This is a long, flat muscle that runs across the abdomen from the ribs to the pubic bone and is separated from the opposite rectus abdominis by the linea alba. Tendinous intersections further subdivide the rectus abdominis on each side into multiple smaller muscle segments.
The rectus abdominis is usually about 10 mm thick, however some athletes have rectus abdominis that can be as thick as 20 mm. In the average inactive individual, the volume of the rectus abdominis muscle is approximately 300 cubic centimeters, while in athletes it can reach 500 cubic centimeters.
Blood supply and nerve supply
The rectus abdominis muscle receives blood from multiple arteries. First, the inferior epigastric artery and vein run upward on the posterior surface of the rectus abdominis and enter the rectus fascia at the line of the arches to supply the lower portion of the muscle. Secondly, the superior epigastric artery is the terminal branch of the internal thoracic artery and mainly supplies the upper muscles. In addition, there is a small segmental arterial supply from the lower six intercostal arteries.
These muscles are supplied by the costoventral nerves (T7-T11), which penetrate the anterior layer of the rectus abdominis fascia. The sensory nerves come from the 7th to 12th thoracic nerves.
Function of the rectus abdominis
The rectus abdominis is an important muscle for maintaining posture. It is responsible for flexing the lumbar spine, such as when the rib cage is lifted up to the pelvis during a sit-up, or for lifting the pelvis toward the rib cage (posterior pelvic tilt), such as when the legs are raised. Both can also be shortened simultaneously when neither side is fixed.
The rectus abdominis aids in breathing and plays an important role when you forcefully exhale, such as after exercise or in difficult exhalation situations. It also helps protect internal organs and increases pressure in the abdominal cavity when exercising or lifting heavy objects.
Clinical significanceAn abdominal muscle strain, also called an abdominal muscle strain, is an injury to the muscles of the abdominal wall. This strain occurs when a muscle is overstretched, causing the muscle fibers to tear. In severe cases, the muscle may even break away from its attachment. This historically benign condition is becoming increasingly common and dangerous as we age and use anticoagulants becomes more widespread.
Many hematomas resolve on their own without treatment, although complete recovery can sometimes take months.
Evolutionary Perspective
As for the evolution of the human rectus abdominis muscle, we can observe it from the basis of anatomy. During the evolution, the rectus abdominis not only has similar functions in various organisms, but the rectus abdominis of different species also differs in the number of tendinous intersections. This shows that adaptation to the diversity of the environment is closely related to the needs of survival.
Under different cultural and historical backgrounds, people have paid more attention to the fitness and shaping of the rectus abdominis, and fitness exercises and various training techniques have emerged in an endless stream. From ancient times to the present, the function and health status of the rectus abdominis muscle have been constantly evolving.
Today, are you curious about your body's health and muscle development?
