Core Form & Function

1. CORE MUSCLES — Muscles that stabilize the spine and pelvis
2. DEEP BACK MUSCLES — Erector spinae (spinal erectors), quadratus lumborum (QL), multifidus muscles
3. INTRA-ABDOMINAL PRESSURE (IAP) — Refers to the “pressure chamber” located in our trunk between the diaphragm, pelvic floor and abdominal walls and describes how core stabilization occurs from the inside out in contrast to external muscular bracing
4. SUPERFICIAL ABDOMINALS — The outermost abdominals: rectus abdominis, internal obliques, and external obliques
5. TRANSVERSUS ABDOMINIS (TA) — Deep core muscle that wraps around torso and supports spine

Introduction

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The term “core” is used inconsistently. Essentially, it is used to refer to many muscles that stabilize the spine and pelvis.

You might be surprised to learn that there is no single anatomical or medical definition of “the core”… Even in the medical/scientific community there are multiple definitions of what constitutes “the core” (source) You can find someone who considers just about every muscle in the body as part of “the core” except the arms, legs, and head, although even the muscles on the back of the neck have been listed as “secondary core muscles” by some. That doesn’t get very specific or tell us much about what the core is. – David Keil 

• The term “core” often refers to the abdominal muscles (outer and deep) and the deep back muscles, including the erector spinae and multifidus.
• More refined definitions also include the diaphragm, pelvic floor and psoas.
• Some definitions include the inner thighs and/or more muscles.

ENCOMPASSING THE ENTIRE TORSO

The subject of “the core” can be a heated one since many people have very different opinions about it and some of them have built entire careers around this topic… Usually when we talk about “the core” we refer to the entirety of your torso between the sternum and the pubic bone. – Olga Kabel

ONE DEFINITION OF MUSCLES OF THE “MIDSECTION”

Here’s a fuller view of your core, or the space between the diaphragm and pelvic floor, wrapping around the torso—also known as “the midsection” and “abdominopelvic cavity.” It includes numerous muscles, superficial and deep: rectus abdominis, internal and external obliques, transversus abdominis, multifidus, erector spinae, quadratus lumborum, and distal latissimus dorsi. It is home to most of your viscera: stomach, spleen, small and large intestines, liver, gall bladder, kidneys, pancreas, bladder, and reproductive organs. – Mary Richards 

EVERYTHING THAT KEEPS LIMBS CONNECTED TO TRUNK

While “core” is often thought of as just the abdominals, anatomically speaking, the core comprises everything that keeps the extremities (that is, the limbs) connected to the trunk — including the major muscles of the back and deep-set stabilizers like the psoas and quadratus lumborum. Accessing the deep core muscles and building strength and heat in the center of the body supports and enhances functional movement. In addition, the yoga tradition holds that it enhances both our physiological and emotional digestion. – Stacey Ramsower 

A DEFINITION RELATED TO FUNCTION

Your core most often acts as a stabilizer and force transfer center rather than a prime mover. Yet consistently people focus on training their core as a prime mover and in isolation. This would be doing crunches or back extensions versus functional movements. – Jeff Kuhland 

MUSCLES THAT STABILIZE & MOVE THE SPINE

“Core” is… a very appealing yoga and fitness buzzword, and teachers and practitioners (myself included) often use it to describe the centrally located muscles that we believe are important to work with. Perhaps my personal favorite definition of “core” might be one I heard from a Pilates teacher: “the muscles that stabilize the spine, and the muscles that move the spine.” That definition, coupled with a practice goal that many of my favorite yoga teachers have offered: “stabilize what’s too mobile and mobilize what’s too ‘stable’ (or ‘stuck’/’tight’),” is, I think, a pretty good framework when it comes to selecting yoga-related “core” exercises. – Kat Heagberg 

See Also

• Core Fundamental Teachings – Features much more detail, including the subject of “stabilizers” vs. “prime movers.”

Functions

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David Keil highlights the fact that the purpose in naming a part of our body “the core” is because we’re interested in its role and how this can help us to optimize the body’s functioning.

A FORM & A FUNCTION

Some of the most recent research defines the core this way: “The core is the foundation of the kinetic chain responsible for facilitating the transfer of torque and momentum between the lower and upper extremities for gross motor tasks of daily living, exercise, and sport.” (Huxel Bliven and Anderson, 2013) And this way: “The core is a 3-dimensional space with muscular boundaries: diaphragm (superior), abdominal and oblique muscles (anterior-lateral), paraspinal and gluteal muscles (posterior), and pelvic floor and hip girdle (inferior).” (Huxel Bliven and Anderson, 2013) Between these definitions, we can get the idea that “the core” is something that has both a location in the body AND has a function. – David Keil 

Thus, let’s look first at the functions of the core as a whole, and then dig into specific muscles.

In Four Main Functions of Your Core Muscles, Olga Kabel of SequenceWiz summarizes them as:

1. Contains and protects the internal organs.
2. Ensures greater mobility of the spine and trunk.
3. Stabilizes the top part of the body over the bottom part.
4. Controls the pelvic-lumbar relationship.

When you’re focused on the outer physical functions, you may wish to highlight these functions as described in a quote below.

1. Stabilizes body position.
2. Transfers force during movement.

CONTROL BODY POSITION & TRANSFER FORCE DURING MOVEMENTS

Your core muscles help control your posture and body position. For instance, the rectus abdominis works primarily to stabilize your rib cage in relation to your pelvis. The transversus abdominis and multifidus work with the pelvic floor and diaphragm to stabilize your lumbar spine. Your core muscles also produce and transfer force during dynamic movements such as vinyasa yoga or running, maintaining spinal stability in order to protect your nerves, disks, joints, and connective tissue. – Mary Richards 

CONTRACTING THE CORE TO CREATE STABILITY

The abs have very limited and specific action, and what experts refer to as the “core” actually consists of many different muscles that stabilize the spine and pelvis, and run the entire length of the torso. When these muscles contract, they stabilize the spine, pelvis and shoulder girdle and create a solid base of support. When this happens, we are able to generate powerful movements of the extremities. – About.com 

in a bit of a side note, David Keil provides a fascinating backstory on the history of teachings about the core, and its importance:

Joseph Pilates (1883-1967), Ida Rolf (1896-1979), and Sri T. Krishnamacharya (1888-1989) were contemporaries. All lived at about the same time. All were explorers in the area of functional movement. All shared a part of their central thesis: There are some muscles, centrally located within the body, that when well trained, can result in the ability to execute actions that appear both strong and light, without being rigid, hard, or forced. All agreed: this kind of relationship with deep internal musculature is subtle and has wide-ranging effects that are physical, mental, emotional, and even spiritual. [See the article for more details.] – David Keil