Ab Anatomy

By: Tana Mardian

“Use your core!”

“Pull your belly button to your spine!”

“Engage your lower abs!”

These are just a few of the phrases you might have heard from a coach in practice, from a trainer in a workout video, or even in your own head when moving some furniture around. But what’s really going on here? What muscles are we talking about?

When thinking about abdominal muscles, the first thing that comes to mind is usually the rectus abdominis, or the “washboard abs” muscle [see Figure 1]. This muscle is visible in people with low fat around the abdominal area, but we all have this muscle, regardless of its external visibility. The rectus abdominis causes trunk flexion, which means it is responsible for bending at the midsection, so crunches are a major workout for this muscle (Saladin, 2018).

Figure 1. Rectus abdominis muscle highlighted in red. https://www.peakptfitness.com/muscle-madness-rectus-abdominis/3020/. Copyright 2017 by Peak Performance Fitness.

The lower part of the rectus abdominis is sometimes dubbed as the “lower abs.” Even though this term is commonly used in the fitness world, the rectus abdominis is one large muscle that can’t be activated regionally by the typical exercising person (Stenger, 2013). This means that if you’re doing a workout that targets the “lower abs,” you’re activating the top part of your rectus abdominis as well. 

The next major set of abdominal muscles is the internal and external obliques [see Figure 2]. While separate, these muscles work in conjunction to rotate and laterally flex (or bend to the side) at the trunk (Jenkins, 2009). The internal obliques work all on the same side: engaging the left internal obliques causes a side bend to the left and rotation to the left, and vice versa for activation of the right internal obliques. When it comes to the external obliques, they will still cause that lateral flexion to the same side, but they rotate the trunk to the opposite side. This means that flexing your left external oblique will cause the trunk to rotate to the right side. The obliques also compress the abdominal cavity and assist with trunk flexion, but all in all, these muscles are our major trunk rotators (Saladin, 2018).

Figure 2. Abdominal muscle anatomy featuring internal and external obliques on left side of image. https://www.bestphysicaltherapistnyc.com/pain-and-symptoms-associated-with-the-external-oblique-muscles/. Copyright by Best Physical Therapist NYC Blog. 

The last and deepest of the major abdominal muscles is the transversus abdominis [see Figure 3]. Its main function is to compress the abdominal cavity, so this is the major muscle working when sucking in the stomach (Saladin, 2018). The transversus abdominis stabilizes the spine, and strengthening it can actually help in the treatment of lower back pain (Gordon & Bloxham, 2016). While it is the deepest of the 4 major abdominal muscles, the transversus abdominis is definitely an important one. 

Figure 3. Transversus abdominis muscle highlighted in red. https://aquacarephysicaltherapy.com/transverse-abdominis-urinary-incontinence/. Copyright 2018 by Aquacare Physical Therapy, Inc. 

Even though the average person can workout without knowing anatomy, being cognizant of what muscles are working can certainly help an individual’s training. It can be useful to visualize what is actually happening during an exercise, and this knowledge can strengthen the mind-body connection that we often strive for in our training. So, the next time you’re sweating through your plank or you’re counting down your last few crunches, let your mind wander to what muscles are firing off and getting stronger. 

Reference List

Gordon, R., & Bloxham, S. (2016, April 25). A Systematic Review of the Effects of Exercise and Physical Activity on Non-Specific Chronic Low Back Pain. Retrieved August 13, 2020, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4934575/

Jenkins, D. B. (2009). Hollinshead’s Functional Anatomy of the Limbs and Back (9th ed.). St. Louis, MO: Saunders.

Saladin, K. S. (2018). Anatomy and Physiology: The Unity of Form and Function (8th ed.). New York, NY: McGraw-Hill Education.

Stenger, E. M. (2013, December 01). Electromyographic Comparison of a Variety of Abdominal Exercises to the Traditional Crunch. Retrieved August 16, 2020, from https://minds.wisconsin.edu/handle/1793/67303

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