Functional Anatomy Part 6-Abdominal Muscles

The abdominal wall consists of four muscles-rectus abdominis, external obliques, internal obliques and transverse abdominis.  When we think of functional anatomy, we tend to focus on how muscles produce motion.  However, the abdominal muscles serve the dual function of both producing and preventing motion as they promote the stability of the pelvis and lower back.  In other words, our abdominal muscles help maintain a neutral pelvis and optimal lumbar (lower back) curve.  Be sure to keep the dual purpose of the abdominal muscles in mind when designing your training programs.  The specific function of each muscle is outlined in the table and paragraphs that follow.

Rectus Abdominis

The rectus abdominis is a long, continuous muscle that extends from the crest of the pubis to the rib cage and xiphoid process.  The primary function of the rectus abdominis is flexion of the trunk, however, the lowest fibers contribute to flexion at the hip joint as well.

  • Exercises: All varieties of crunches/sit-ups, reverse crunches, dead bugs, planks

Internal and External Obliques

The internal and external obliques rely on each other to produce movement, so we’ll examine them together.  The internal and external obliques are lateral to the rectus abdominis, with the internal oblique sitting deep to the external oblique.  They produce various movements depending on which portions are recruited.

When both the left and right sides contract equally, they produce a net movement of trunk flexion, aid in compression of the abdominal wall and increase intra-abdominal pressure.  When each side acts individually, they aid the spinal erectors and quadratus lumborum in producing trunk rotation and lateral flexion.  When producing rotational movements, the internal oblique on the side you’re twisting to contracts with the external oblique on the side you’re twisting from.  When contributing to lateral trunk flexion, the same-side internal and external obliques work together to produce the movement.

  • Exercises: Russian twists, full-contact twists, cable chops, medicine ball v-sit twists, windmills, side bends

Transverse Abdominis

The transverse abdominis is the deepest muscle of the abdominal wall.  Its primary function is to compress the abdominal contents and aid in production of intra-abdominal pressure.  In other words, the transverse abdominus reduces the diameter of the abdomen.

  • Exercises: vacuums, plank variations, abdominal bracing in the quadraped (on all fours) position, dead bug variations and any movement that requires you to brace or stabilize your spine against a load (i.e. squats, deadlifts, overhead presses, etc.)

Considerations for Training

Training the abs is important because a strong core is critical for stabilizing the body during heavy lifts, activities of daily living and sport specific movements.  The problem is, most people don’t train them properly.  If I walked into a commercial gym and asked a hundred people what exercises are best for your abdominals, I’m sure most of them would answer sit-ups and crunches.  Sit-ups and crunches only train spinal flexion and there are a number of problems with these exercises…

  • They place too much compressive force on the back.
  • Repetitive flexion and extension of spine often leads to injuries (don’t believe me? I suggest you read some of Stuart McGill’s research).
  • Too much trunk flexion work will actually shorten your rectus abdominis resulting in a kyphotic or slouched upper body posture…Think Quasimodo…

So…step number 1 for improving your abdominal training program, ditch the sit-ups and crunches and instead, include exercises for all of the basic abdominal functions: flexion, rotation, lateral flexion, and stabilization.  There are a number of different ways to implement this plan but a simple method is to train one or two of these movement functions during any given training session.  For example, if you workout four days a week use flexion-based exercises one day, rotational exercises on another and so on…Lets discuss in each movement in greater detail…

Flexion Exercises

Before I get into discussing flexion-based abdominal exercises I need to point out one thing…  There is no such thing as “upper” and “lower” abdominal muscles.  The upper and lower portions of the rectus abdominis muscle have a common nerve supply so they can’t be isolated into upper and lower sections.  However, for ease of explanation, when I refer to “upper abdominal exercises” in this section I am referring to the trunk flexion function of the rectus abdominis.  Alternatively, when I refer to “lower abdominal exercises,” I’m talking about pelvic stabilization, posterior pelvic tilt or anti-extension functions of the rectus abdominis.

Examples of upper rectus abdominis exercises include:

Examples of lower rectus abdominis exercises include:

If you’ve spent a fair amount of training time working only on flexion-based abdominal exercises it’s probably a good idea to dedicate some time to the second function of the rectus abdomens: stabilization and posterior tilt of the pelvis.  Exercises like reverse crunches, dead bugs and leg lift variations (if you’re abs are strong enough to do them properly) are far more adventageous than crunches and sit-ups because they help to maintain a neutral pelvic alignment.  This in turn will help to reduce pressure and pain in the lower back.


Rotational exercises should be included because many sport specific and everyday movements involve twisting with a load.  Moreover, rotation-based abdominal exercises promote thoracic spine mobility (as long as the pelvis is stabilized throughout the movement). The prime movers during rotation-based exercises are the external obliques, but the internal obliques and rectus abdominis help produce torque and coordinate the movement.  Examples of rotation-based abdominal exercises include:

Lateral Flexion

Lateral flexion exercises are often neglected.  More often than not, when I see people doing lateral flexion exercises they generally perform plate or dumbbell side bends…an OK exercise, but there are others that I think are better…Oh, a tip for those of you that include side bends in your program, it doesn’t really work if you hold weight in both hands, picture a seesaw with the same amount of weight on each end, it wouldn’t move right?…so if you’re going to do side bends, only hold weight in one hand!  If you’re bored of simple side bends, try the exercises below:


Core stability is the the ability to maintain neutral torso and pelvic alignment while resisting motion imposed by the extremities.  It is important because a lack of stability can result in a number of lower back, upper extremity and lower extremity issues (a lack of mobility will result in these issues as well but we’ll discuss that some other time…).  By including core stability exercises in your program you will improve muscle recruitment, posture, and tone while preventing injury.  Core stabilization exercises fall into four categories: anti-extension, anti-rotation, anti-lateral flexion and hip flexion while maintaining a posterior pelvic tilt.

The goal of anti-extension exercises is to resist lumbar extension by bracing the abdominal and gluteal muscles to produce hip extension.  Examples of anti-extension exercises include:

When performing anti-rotation exercises the goal is to resist rotation around you lumbar spine.  To do so, brace your abdominal and gluteal muscles to stabilize your pelvis.  Examples of anti-rotation exercises include:

Anti-lateral flexion exercises involve resisting a side bending motion.  Examples of anti-lateral flexion exercises include:

Many people find it very difficult to produce hip flexion while maintaining a posterior pelvic tilt.  Those people that have tight hip flexors will find it particularly challenging because their abdominal muscles are often inhibited and their short hip flexors have a tendency to pull their pelvis anteriorly.  Because of the difficulty involved with performing exercises that challenge this function, they are often eliminated.  However, exercises that challenge your ability to maintain a neutral spine while producing hip flexion are essential because they help to maintain a neutral pelvic alignment both in and out of they gym.  Examples of exercises that train this function include:

There you have it…A somewhat short summary of how the abdominal muscles function and what you should take into consideration when designing your programs.  Before we conclude however, I’d like to leave you with one more point to ponder…  I find that many people have the tendency to do very high repetition training for the abdominal muscles.  Why would anyone do this?…  Remember that the abs are just like any other muscle group, in order to improve strength and definition, you have to load them, it’s ineffective to just continually tack on reps.  Use the overload and variability principles just as you would for any other muscle group.

Finally, I’d like to introduce an exercise that incorporates all of the abdominal functions discussed in this article, the Turkish Getup.  This is an exercise that I include quite often in my programming because it has a number of benefits beyond increased core strength and stability, it also improves hip mobility, hip extension, thoracic extension and shoulder stability…Click the link below for a description.

Until next time…Enjoy shredding those abs!  Adios for now.

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