Abdominal Muscles Location and Function

It seems everyone who exercises is looking for the best ab routine for developing flat, tight abdominal muscles. Every year there are dozens of new exercises, fitness classes, products, gadgets, or routines claiming to sculpt and strengthen the abdominal muscles. And while some of these may offer a new approach to working the abs, many are ineffective and may increase your risk of injury.

To avoid falling victim to unproven and misleading abdominal exercise claims, it's important to have an understanding about the function of your abs, including where they are, what they do, and how they can be exercised with the least risk of injury.

1

Rectus Abdominis

Anatomical model showing the lower abdominal muscles.
Getty Images/Science Picture Co

The most well-known and prominent abdominal muscle is the rectus abdominis. It is the long, flat muscle that extends vertically between the pubis and the fifth, sixth, and seventh ribs. The rectus abdominis connects to the xiphoid process, a bony landmark at the bottom of the sternum.

A strong, tendinous sheath called the "linea alba," or white line, divides the rectus abdominis down the middle, and three more horizontal tendinous sheaths give the muscle its familiar "six-pack" look in very fit athletes.

The rectus abdominis helps to flex the spinal column, narrowing the space between the pelvis and the ribs. It is also active during side bending motions and helps stabilize the trunk during movements involving the extremities and head.

2

External Obliques

External Oblique Muscle
Science Picture Co / Getty Images

The next group of muscles that make up the abdominals is the external oblique muscles. This pair of muscles is located on each side of the rectus abdominis. The muscle fibers of the external obliques run diagonally downward and inward from the lower ribs to the pelvis, forming the letter V. You can locate them by putting your hands in your coat pockets.

The external obliques originate at the fifth to twelfth ribs and insert into the iliac crest, the inguinal ligament, and the linea alba of the rectus abdominis.

The external oblique muscles allow flexion of the spine, rotation of the torso, sideways bending and compression of the abdomen.

3

Internal Obliques

External and internal oblique muscles
Science Picture Co / Getty Images

The internal oblique muscles are a pair of deep muscles that are just below the external oblique muscles. The internal and external obliques are at right angles to each other.

The internal obliques attach from the lower three ribs to the linea alba and from the inguinal ligament to the iliac crest and then to the lower back (thoracolumbar fascia). The lower muscle fibers of the internal obliques run nearly horizontally.

Along with the external obliques, the internal obliques are involved in flexing the spinal column, sideways bending, trunk rotation, and compressing the abdomen.

Because of their unique alignment, at right angles to each other, the internal and external obliques are referred to as opposite-side rotators. Both do side bending to the same side, but the external oblique on the left rotates the trunk/spine to the right, whereas the internal oblique on the left rotates the trunk/spine to the left.

4

Transversus Abdominis

Transversus Abdominis Muscle
SEBASTIAN KAULITZKI/SCIENCE PHOTO LIBRARY / Getty Images

The deepest layer of abdominal muscles is called the "transversus abdominis." The transverse abdominal muscle wraps around the torso from front to back and from the ribs to the pelvis. The muscle fibers of the transversus abdominis run horizontally, similar to a corset or a weight belt.

This muscle doesn't help move the spine or the pelvis, but it does help with respiration and breathing. This muscle helps facilitate forceful expiration of air from the lungs, stabilizes the spine, and helps compress the internal organs. It also helps to support the abdominal wall and and compress the abdomen.

5

Hip Flexors

Human leg musculature, computer artwork.
SHUBHANGI GANESHRAO KENE / Getty Images

The hip flexors are a group of muscles that bring the legs and trunk together in a flexion movement. The hip flexors are not technically abdominal muscles, but they do facilitate movements during several ab exercises. The muscles tha make up the primary hip flexors are:

  • Psoas major
  • Illiacus
  • Rectus femoris
  • Psoas minor

Many so-called ab exercises actually work the hip flexors more than the abs. The hip flexors are strong, powerful muscles that can overtake the abdominal muscles in some ab exercises. In order to isolate the abdominals, you need to minimize the involvement of the hip flexors and maximize the contraction of the abdominals.

One example of an ab exercise that actually focuses on the hip flexors includes the full sit-up exercise, especially when the feet are held down. This movement primarily involves the hip flexors and may cause the lower back to arch. This could increase the risk of back pain, particularly if you have weak abdominal muscles. Therefore, the full sit up is not recommended for beginners.

Another example of an ab exercise that works the hip flexors is any leg-raising exercise done in a supine (lying face up) position. Again, this movement works the hip flexors far more than the abs and shouldn't be done until you have good abdominal strength. The best way to isolate the abs is to minimize the involvement of the hip flexors while doing your ab workout.

6

Design an Effective Abdominal Exercise Routine

Hispanic woman balancing on fitness ball near brick wall
Peathegee Inc / Getty Images

Now that you have a basic understanding of what the abdominal muscles are and how they work, you can design workouts that actually target these muscles. Select 5 to 10 exercises that combine these four elements. Perform 10 reps of each exercise, then move on to the next. Change your exercise routine every 2 to 3 weeks.

Spinal Flexion

  • Ab crunch on an exercise ball
  • Long arm crunch
  • Reverse crunch
  • Basic crunch
  • Captain's chair

Rotation

Extension 

Stability

Isometric exercises (such as the plank and the bird dog) that focus on limiting trunk movement are great abdominal exercises. One more option is the pallof press—an antirotation movement that strengthens the core.

To perform the movement, use a band or cable that is fixed to a steady surface at torso height. Stand far enough away from the band so that when you hold the band in front of your sternum, there is tension. When you are facing forward, the band will be affixed on your side.

Extend your arms (and the band) fully in front of your chest, then bring them back in close to your chest. Resist giving in to the side pull and rotating your torso toward the band's anchor.

Use Good Form

  • Contract your abs and pull your bellybutton in toward your spine with each contraction.
  • Move slowly and with control.
  • Support your head when you need to, but don't pull on your head or pull your chin to your chest.
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  1. Kim E, Lee H. The effects of deep abdominal muscle strengthening exercises on respiratory function and lumbar stabilityJ Phys Ther Sci. 2013;25(6):663-665. doi:10.1589/jpts.25.663