Meet Your Muscles: Abdominal Muscles Anatomy

In order to see those abdominal muscles rippling like plates of armor, you must combine aerobic exercise—walking, running, treadmill workouts, stair climbing, and the like—with abdominal workouts and proper eating. The ab exercises  aren’t miracle workers, and they can’t produce washboard abs in a matter of days. Combined with an overall fitness plan, though, they are effective. The only way those muscles will ever reveal themselves is to trim body fat. You can do crunches and situps from down until dusk, but until you strip away those surface layers of fat, the muscles themselves stay out of sight. Unfortunately, many people still buy into the notion that abdominal exercises melt fat off your midsection. Unlike bench presses which produce visible changes in as little as a few weeks, crunches and other abdominal exercises produce more subtle results.

A narrow waist and tight midsection will accentuate the development in your shoulders, chest, and arms. You can’t achieve the extreme V shape necessary in bodybuilding without a small waist.

Well-defined abdominals are the product of hard training, careful eating and low body-fat levels. If you are after a rippling six-pack, you need to reduce your abdominal fat layer for the muscles to show through. Increasing their size alone through exercise will not be enough. For these muscles to become visible, men need to have 10-12 per cent body fat and women need to have 15-18 per cent body fat – ranges that are below those considered healthy among the general population but that are compatible with improved sports performance.

Abdominal Muscles Anatomy

The abdominal wall can be divided into two separate anatomic parts, each of which functions differently. The front wall consists of one muscle, the rectus abdominis (also known as the “abs”). The rectus abdominis starts near the middle of the sternum and runs vertically to below your navel. It is this muscle group that, when well-developed, give guys that layered “washboard” or “six-pack” look. The two rectus abdominis muscles (one on each side) are encased in a sheath of fascia that forms the central demarcation down the middle of the abs, known as the linea alba. Fascia divisions in the muscles are responsible for the “six-pack” appearance. If you can see your linea alba right now, congratulations; you’re leaner than we are. The lower rectus actually has two segments beneath the belly button, but it’s nearly impossible to get so lean and muscular that this muscle separation is visible.

On most people, a perfectly developed rectus abdominis has six segments of muscle above the belly button (the “six-pack,” or upper abs) and a flat sheath below (the lower abs). The terms upper abs and lower abs are therefore slightly inaccurate since the rectus abdominis is really one muscle. But the sensation in the muscle when you do crunches (which work its upper, segmented portion) is different from the feeling you have when you do reverse crunches (which engage the lower, flat section). So it’s easiest to talk about the rectus in terms of where you feel the effort when you exercise.

Thanks to individual genetics, you could have a four-pack or even an eight-pack above your navel instead of a six-pack. Or you could have six segments aligned asymmetrically.

The side wall consists of three layers of muscles – the internal and external obliques, and the transverse abdominis. The external oblique is the outer visible layer that passes obliquely downward from the rib cage to the pelvic bone (located on the sides of the rectus abdominis). The middle layer is the internal oblique that passes obliquely upward from the pelvic bone to the ribs. Internal oblique lies under external oblique, and the fibers of the two muscles pass at right angles to one another. Put another way, the external oblique fibers run diagonally downward from the middle of the rib cage, while the internal oblique fibers run diagonally upward from the pelvis.

The innermost layer is the transversus (transverse) abdominis, which lies horizontally across the abdominal wall.  As you can see from the image above, the internal obliques and transverse abdominus cannot be seen because they lie beneath the rectus abdominis and external obliques.

MUSCLES / FUNCTIONS	ORIGIN	INSERTION	MAIN FUNCTIONS
RECTUS ABDOMINIS	5th, 6th and 7th ribs, xiphoid process of the sternum	pubis (pubic symphysis and arms)	bending the torso forward
EXTERNAL OBLIQUE	ribs (7th or 8th and last)	iliac crest, inguinal ligament	flexion of the torso, bending to same side and turning to opposite side (acting on one side only), lowering the ribs
INTERNAL OBLIQUE	ribs (last 4)	inguinal ligament, iliac crest, lumbodorsal fascia	flexion of the torso, bending and turning to same side (acting on one side only), lowering the ribs
TRANSVERSE ABDOMINAL	lumbar vertebrae (vertex of the transverse apophyses)	pubis (upper edge of the pubic symphysis and pubis)	compression of the natural abdominal girdle

Easy to remember: The main abdominal muscle that runs down the middle of your body is the rectus abdominis. It’s the large, flat muscle wall that – assuming it’s not hidden by fat – defines most of the front of your midsection from the lower chest to the pubic bone. The obliques on the sides of your body allow you to twist. The transverse abdominis runs across your abdominal region to provide support for posture and movement.

Function of the Abdominal Muscles

The rectus muscles cause flexion of the trunk, bending the torso forward toward the legs. The motion is carried out by the upper abs, which pull the rib cage down toward the pelvis, or by the lower abs, which lift the pelvis upward toward the chest.

Contraction of the oblique muscles on one side causes the torso to bend sideways. Contraction of the obliques simultaneously on both sides assists the rectus muscle in flexing the trunk and also splints the abdominal wall whenever a weight is lifted.

The transverse and oblique abdominal muscles form an excellent natural girdle, compressing the abdomen, but they are normally relatively untrained. The transverse abdominis is responsible for holding your internal organs in place (preventing the internal organs from pushing your belly outward) and forcing air out of your body. It doesn’t have any direct role in flexing, twisting, or straightening your spine.

The importance of having strong ABS

Besides looking awesome, what is a benefit of having strong abs? If your abdominal muscles are weak, you are more susceptible to having a weak back and poor posture. Many people suffer back injuries, in part because they haven’t developed their abs. Taller, heavier men sometimes have more trouble achieving outstanding definition in their abs, but that doesn’t mean they shouldn’t work at it.

Abdominal muscles are amazingly useful when playing sports. When you’re kicking a soccer ball, for example, they help you generate more power. More important, they can help you play harder and stay injury-free longer. And they assist you in weight training other muscle groups.

The notion of washboard abs creates a great deal of anxiety and insecurity among many individuals. Unless you have the genetics to not store fat above your rectus abdominus muscle, the tone of your abdominals, no matter how fit you are, will show directly under your skin. Models and celebrities often have this fat vacuumed out through liposuction to reveal the muscularity underneath or they have airbrush contour tans sprayed on to give the appearance of ‘cut’ abs. Feel good about yourself from simply knowing that you have strong abdominal muscles, regardless of whether the world can see them or not.

Abdominal Exercises

The abdominal exercises are divided into upper-abdominal exercises, lower-abdominal exercises, oblique exercises, and core exercise. Wherever a certain type of exercise is used in a workout, any one of the same type can be substituted.

Ab exercises are intended to create shape and separation in the muscles of your midsection, but it’s possible to develop your abs too much, so that your waistline grows instead of shrinks—you would lose the effect you were after in the first place! For this reason, most ab exercises don’t involve weights. Your own body weight provides enough resistance.

Since these muscles tense powerfully in many exercises for other parts of the body, these are often confused with specific workouts for the abdomen.

If you need to choose which part of the abdomen to train first, start with the external and internal obliques. Finally, it is not necessary to stretch the muscles of the abdomen. They do not need it, and it is not recommended (they are relaxed when standing normally).

All effective ab exercises use some type of “crunching” motion—contracting your abs. This can be done either by bringing your rib cage down toward your waist or by bringing your waist up toward your rib cage.

Unlike other weightlifting movements, exercises for the abdominal core and especially those for the rectus abdominis absolutely must be worked with a rounded back (rolling up the spine).

When performing exercises that roll the spine up off the floor, as in crunches, you hold the spine differently than when performing squats, deadlifts, or other standing movements (where the vertebral column is arched at the lumbar spine).

If the back is not rounded with intense contraction of the rectus abdominis and the internal and external obliques, the powerful psoas hip flexors will increase the lumbar curve, forcing the intervertebral discs forward. This causes increased pressure at the posterior lumbar vertebral articulations, which can cause low back pain or, more seriously, articular compression or shearing.