January 2021
The Deep Core: It’s Not Your Six-Pack
Many people think of a flat stomach and those oft-coveted six-pack muscles when they hear the word “core”. The six-pack muscle is the rectus abdominus, which is a superficial muscle, or muscle that is more on the outside of the body, that does not have attachments to the spine. Therefore, while it may look good when toned, and is an important muscle, it does not stabilize your spine. Think instead, of the deep core as a three-dimensional box throughout your trunk with muscles on all sides that attach to your spine, pelvis, ribs, ligaments, and thick fascia, which is connective tissue, in the front and back of your torso. Below I will discuss the muscles of the deep core, as well as some other important core stabilizing muscles.
Deepest Layer of Core Stabilizers:
Transversus Abdominus: The transversus abdominus (TA) is, in my opinion, the most important stabilizing muscle in your body. It is a large muscle that wraps around your entire lower trunk/waist, acting like an internal corset. It is the deepest abdominal muscle, and due to its large size and multiple attachments, it helps to stabilize the spine, in part by maintaining normal abdominal wall tension. The TA is activated prior to extremity (arm or leg) movement in order to help increase stiffness of the spine for stability. When the TA is contracted, it is like cinching up the corset to help provide support for the spine.
Low back pain is one of the leading reasons people seek medical advice in this country, and has a recurrence rate of over 60%. While there are many causes of and forms of low back pain, spinal instability has been found to be an important cause for recurrent low back pain. The TA is known to play a large role in spinal stability, and studies have shown that the TA atrophies following an episode of low back pain. Additionally, people with low back pain have been shown to have a decrease in TA activation following an episode of low back pain. Through working with a physical therapist, you can learn how to properly activate and strengthen the TA in order to improve and/or prevent injury and function at your highest level.
Diaphragm: The diaphragm is a dome-shaped sheet of muscle that separates the thoracic cavity, which contains the heart and lunges, from the abdominal cavity. The diaphragm is the main muscle responsible for respiration (breathing), and is a key component to core stability, due to its multiple attachments and the fact that it assists in maintaining abdominal wall tension. When we breathe in, the diaphragm lowers into the abdominal cavity, helping to suck air into our lungs, and when we breathe out, the diaphragm rises back up to its resting position. Studies have shown that the diaphragm has a postural function that can be voluntarily controlled and is independent of breathing. Additionally, it can perform its dual functions of stabilization and respiration simultaneously. The diaphragm has been shown to activate, along with the TA, to stabilize the spine prior to limb movement, and evidence has shown that people with a limited ability to contract the diaphragm for stabilization have an increased risk of developing low back pain.
Multifidus: The multifidus is a series of small, triangular muscle bundles located deep in your back along either side of the spinal column, and is one of the deepest layers of back musculature. It extends vertically along all parts of the spine including cervical (neck), thoracic (upper and mid-back), lumbar (low back), and sacral (pelvis) regions. It is the thickest in the lumbar spine region. The multifidus helps extend the spine (lean backwards) with the help of other, larger muscles along your back. It also contributes to bending sideways and rotating, though perhaps its most important function is helping to stabilize the spine. Its unique design has been thought to endow it with extra strength, as the connections help stabilize individual vertebrae (the bones that make up your spine) as other parts of your spine move. The multifidus is connected to the TA via thoracolumbar fascia, which is thick connective tissue in your lower back, and the multifidus and TA “co-contract”, that is, they contract together to help stabilize the spine. Studies have shown that trigger points (areas of tight/spasming muscles) in the multifidus can decrease the contraction efficiency of TA, and that multifidus weakness and atrophy is associated with chronic low back pain.
Pelvic floor muscles: The pelvic floor is a group of muscles located in your pelvis that stretch like a hammock from the pubic bone (at the front) to the coccyx or tail-bone (at the back) and from side to side. The pelvic floor muscles work with your deep abdominal (TA) and deep back muscles (multifidus) and the diaphragm to stabilize and support your spine. They also help control the pressure inside your abdomen to deal with the pushing down force when you lift or strain - such as during exercise. Pelvic floor muscles also help maintain bladder and bowel control and play an important role in sexual sensation and function. Pelvic floor muscles can be strengthened by doing pelvic floor muscle exercises. You can learn more about the pelvic floor by working with a physical therapist that is specialized in this area, known as a Pelvic Floor Physical Therapist.
Additional Core Stabilizers
Obliques: The obliques, which run along the sides of your core and are exterior to the TA, are important for rotational movements, bending from side to side, and protecting your spine. We have two sets of obliques: internal and external, with the fibers of each running perpendicular to each other. Together, the obliques and TA increase intra-abdominal pressure necessary for the support of the vertebral column to help us perform our daily functions, as well as exercise.
Gluteals: Maximus, Medius, & Minimus: You may have heard of a set of muscles known as your “glutes”, or butt muscles. We have 3 sets of gluteal muscles: maximus, medius, and minimus. The gluteals contribute to stabilization of the lower back and pelvis/hips, along with our deep hip rotator muscles. The gluteus medius and minimus are deep (underneath) the gluteus maximus, and are abductors and internal rotators of the hip that contribute to stabilization of the hip ball and socket joint and alignment of our pelvis. The gluteus maximus is a large, powerful muscle that makes up the bulk of your butt cheeks that extends and externally rotates the hip. Research has shown that contraction of deep abdominal muscles (TA) may assist with contraction of the gluteus maximus to assist with pelvic stability. Decreased stability of the hip joint and pelvis can lead to poor leg alignment and impaired transfers of forces between our spine and limbs with walking, running, and strength training, which can lead to pain or injury, and weakness of the gluteal muscles has been associated with a number of lower limb injuries.
My Introduction to the Core – Martial Arts
Before I became a physical therapist and learned all about anatomy and human function, I learned about the importance of the deep core muscles and energy concentration from my Sifu (kung fu teacher) James Banks. He always emphasized that when you tighten the core, everything becomes stronger, more powerful, and more alive. He taught me about the lower dantian, which in Chinese culture is the energy (or “qi”) center located in the lower abdomen. There are actually three dantian, Spiritual, Energetic and Physical, which are the energy flow and concentration centers, important focal points for meditative and exercise techniques such as qigong, martial arts (kung fu and tai chi), and traditional Chinese medicine. The lower dantian (Physical), or what we generally think of as the core, is particularly important as the focal point of breathing technique as well as the centre of balance and gravity. Through practicing with an increased focus on keeping my core engaged, I found that my balance and kicks were more stable, and my punches and blocks were more effective, though I didn’t know all of the “why”.
Why Is the Core So Important? Protection & Power!
In short, the core is key to our daily activities and exercise because it stabilizes our bony skeleton, most importantly, our spine, which is just a flexible bony column. Stability of the spine involves three systems: passive, active, and neural control.
The passive system includes ligaments, joint capsules, and other non-contractile tissues, which provide stability at the end ranges of motion. Unlike muscles, ligaments do not have almost any elasticity, and once stretched out, they do not shrink back to their original length. In order to help preserve the integrity of our ligaments and other connective tissues, such as joint capsules, we must use the active system.
The active system includes the muscles surrounding the spine that provide support for our bony frame and produce the forces necessary for stability. This in turn allows our big movers, like our quads and hamstrings, deltoids and biceps, to move our limbs in a coordinated and controlled manner, and also to produce sufficient strength to do the things we want to do. As mentioned above, our deep core muscles including the TA, diaphragm, and multifidus, contract prior to our limb movement, in order to stabilize the spine to prepare the body for that movement. If we do not have stability of our spine, it will move excessively with the movements of our arms and legs, which can cause increased stress on structures within the spine, including the discs.
The neural system includes our brain and nerves, which receive information from our trunk and extremities and send signals for muscle activation and motor patterns for spinal stability. Through improving muscle strength and motor patterns, we can improve spinal (and pelvic) stability, which can improve how we feel and function.
How To Improve Your Core – Thinking Beyond Sit-Ups
People have many different thoughts about what our “core” is, and one of the exercises I hear discussed often as the best, or most well-known core exercise, is sit-ups. Sit-ups strengthen the rectus abdominus, that six-pack muscle, and are fine to do if you can perform them without pain during or afterwards. However, as mentioned above, the rectus abdominus does not attach to the spine, therefore it does not contribute significantly to spinal stability.
To strengthen the deepest core muscle, the TA, you must first learn how to properly contract it. To find the TA, place an index finger on each side of your belly button, about an inch away and slightly lower, near your belt line, and press into your stomach a little with your two fingers. Perform a gentle laugh or cough, and you should feel a muscle, the TA, contract, or harden, underneath your fingers. It can be challenging to learn how to contract this muscle, it is not simply sucking your stomach in. Learning how to contract the TA may be harder for some people than others, based on your previous experiences, including if you have a history of low back pain, past or current pregnancy, or other factors that can affect your ability to contract this muscle.
Once you are able to consciously isolate and contract your TA, the next step is to learn to co-contract it in conjunction with other muscles of the core. The next stage is learning how to co-contract the entire core (TA, diaphragm, multifidus and pelvic floor) in coordination with larger superficial muscles during functioning activities and exercise. To strengthen the deep core, you can perform increasingly challenging movements with your legs while on your back, keeping your spine and pelvis stable and in a neutral position. You can further strengthen it by then contracting and stabilizing with the core while you perform exercises in more challenging positions, such as front or side planks, quadriped (hands and knees) exercises, or standing activities. Adding weight to an exercise increases the challenge on TA and the other deep core muscles to stabilize the spine and pelvis as it increases the load on our levers – arms and legs. Working with a physical therapist to learn how to improve your core stability can be beneficial as we are able to take into account your past history and current level of function to teach and progress you at your individual skill level. By improving your core stability, you can minimize pain and injury, and do the things your enjoy with greater ease and power!
References:
6. https://www.verywellhealth.com/multifidus-muscle-296470
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