Second in our series all about the core, let’s take a look at the anatomy of the core, which is far more complex than the anterior abdominals (that 6-pack Erin referenced in our series lead-off post).

The core is actually comprised of many of our primary muscles and can comprehensively be considered all of the muscles that attach to our pelvis and spine. This includes muscles such as the gluteus maximus & gluteus medius (buttox), hip flexors, hamstrings, abductor and adductor complexes (those muscles that allow our legs to move laterally), and the latissimus dorsi that links the shoulder blades, upper arms and spine. However, for this article we will concentrate on the more traditional “core” of the core – pubic bone to the sternum, and how these muscles contribute to enabling the activities referenced in the previous article.

This “core” group of muscles includes those that keep most of our internal organs safe in lieu of rigid bone structure, allow us greater mobility in our spine and trunk, stabilize our upper body to remain upright above the lower body, and control the lumbar (low back)/pelvic complex. Clearly these muscles hold critical functions that are vital to our everyday livelihood and movement, so it’s no wonder that we so often here “strengthen your core!” Let’s look at some of the specific muscles (groups of muscles) and their primary functions to understand why it is important to incorporate a holistic approach to strengthening the core muscles as part of any training regimine.

Rectus Abdominis

The rectus abdominis are those muscles that create the washboard abs affect, extending vertically the entire length of the abdomen. Besides creating a “good look” these muscles perform critical function by enabling flexion of the torso and spine – this is why we can bend forward to pick something up or do a traditional sit up. These muscles also play an important role in controlled breathing, particularly exhaling forcefully, and in bracing – both used particularly when lifting heavier loads.


There are two sets of oblique muscles, internal and external, located on either side of the body, with the internal obliques located just below the external and above the transverse abdominis. These muscles work together to allow us to bend laterally to each side and to rotate around the spine. In addition, these muscles also play an important role in controlled breathing during exhalation, which is often used during weight lifting and exercise.

Transverse Abdominis

The transverse abdominis is one of the innermost layers of the abdominal muscles, located beneath the rectus abdominis. These muscles draw the belly to the spine to activate the core and stabilize the pelvis and low back prior to body movement. This means the transverse abdominis muscles are recruited almost any time we move our limbs – which you may agree is pretty important for daily movement!

Erector Spinae

The series of muscles that lie on either side of the vertebral column and extend alongside the lumbar, thoracic, and cervical sections of the spine, is known as the erector spinae. These muscles allow us to stand back up after bending over and to perform a (slight) back bend. Although we are concentrating on the central core muscles, one function of the erector spinae illustrates a perfect example of how the core extends beyond our center. The erector spinae muscles work together with the hamstrings and gluteus muscles to enable trunk extension – standing back up from a bent over position.

Quadratus Lumborum

The quadratus lumborum, commonly known as the back muscle, is the deepest of the core muscles and is located on either side of the lumbar spine (low back). It starts at the lowest rib and ends at the top of the pelvis, connecting the spine to the pelvis. With these connection points, it is responsible for stabilizing and controlling movements of both structures – spine and pelvis. This includes contributing to lateral flexion of the spine (side to side bending) and extension of vertebral column. In addition, the quadratus lumborum assists the diaphragm with inhalation while breathing.

As we can see, the core muscles work together to enable the dynamic and stable movements of our entire body, each playing an indispensable role in our mobility. So, keeping in mind the full range of muscles and their functions can create a more comprehensive and effective core strengthening regime.

Watch for the next articles in our core series where we’ll go into detail about planes of motion and key exercises!

Author Molly Gates is a personal trainer at Hyatt Training. She believes every person has an incredible opportunity to reach new levels of success. By providing structure, support, guidance, accountability, and encouragement, she help clients feel better inside and outside the gym. Get in touch with her by emailing us at

Hyatt Training is a collective of certified, enthusiastic and innovative personal trainers in Portland, Oregon. To read more exercise-related posts like this one, follow this link.