top of page
  • Writer's pictureMelissa Buehler

The Deep Core & "Good Posture"

Updated: May 12, 2023

Do you feel like you’re falling apart? Everything aches or you are experiencing one injury after another?

There could be a multitude of reasons you are falling apart. Unhealthy eating, sleeping too little, allergies/sickness and high stress, can all increase inflammation in the body. Past injuries, muscle weakness, inflexibility and poor posture can also contribute to pain.

When a person begins to fall apart and winds up in my clinic, we often start with posture training and movement analysis. Why? The way you hold your body and move is the foundation needed to build a strong body and reduce pain/injuries.

What is the Deep Core?

Most people think of a rocking six pack when they hear strong core. Or maybe it’s the Transverse Abdominis if you practice Pilates? While these muscles are part of the core, understanding the core more as a stabilizer or a force transmitter, will help you use your body more efficiently.

The core consists of all the muscles in the trunk of your body. This is the area from the pelvis to the collarbones. Yes, the rocking six pack is part of this region, but its purpose is to flex the trunk, a phasic muscle. While the other, much smaller, and deeper muscles in this area, are the tonic muscles (including transverse abdominis). These are also known as the stabilizers or postural muscles; I am going to call it your deep core.

Phasic muscles are the big, strong muscles of the body that produce movement. Rectus abdominis (a flexor) and paraspinals (extension) are examples of phasic muscles in the core. Dr. Stuart McGill, PhD, developed a philosophy based off of his research on these muscles for back pain. In his treatment paradigm, if you strengthen the these multi-joint muscles, you will reduce back pain. This is accomplished by reducing the strain on your ligaments from the lack of strength currently present.

The tonic muscles are the posture muscles that help keep a human erected. In the core, transverse abdominis, the pelvic floor, diaphragm and multifidi are examples of these muscles. We don’t have to think about engaging these muscles when moving, this should automatically occur.

Dr. Paul Hodges, PT, PhD, is a researcher who was one of the first to study the deep core activation and its relationship to back pain. He found that the deep muscles of the core (specifically the multifidi) become inhibited after injury and back pain. He also showed that this inhibition can remain much longer after the injury has healed. This is part of the reason why back pain is recurrent.

Since the tonic muscles are under automatic control, it can be hard to strengthen these muscles. Fortunately, these muscles can be revived through training. This is done through isometric holds that target specific areas of weakness in the back or core. It is reinforced through posture training and then transferred into strength/functional training.

As mentioned previously, these muscles are automatic, we shouldn’t have to think about turning them on when we get hurt. We just need to learn how it feels when they are working efficiently and know when they are not (and how to fix it!).

The Soda Can Analogy

Dr. Mary Massery, PT, DPT, DSc, has done extensive research on breathing and posture. Her findings have led to the development of the "soda can" analogy, commonly used when describing the deep core system.

If you take an empty soda can and apply force to its ends, either between the palms of your hands or even by standing on it, it will not break. Take the same soda can, but with a small dent in it, and repeat the same test it will crumple. The inherent strength of the non-dented soda can is due to the pressure of the vessel, not the aluminum it is made from. This helps explain the pressure systems of the body, the foundation to an efficient core.

There are three pressure systems in the core: the abdomen, the thoracic (lungs) and the larynx (throat and mouth). Let’s focus on the abdomen. The top of the "soda can" is your diaphragm, the bottom your pelvic floor. The walls of the can are made up of the muscles that make up the sides of our body (transverse abdominis, lumbar fascia, multifidi, obliques, etc).

If we pull our shoulders back and suck our tummy in as we are told is “good posture”, you get a dent in the back of the "soda can". If you spend a lot of time looking down at your phone or stand with crossed arms, you get a dent in the front. These dents change the pressure systems, compromising the inherent strength of our bodies.

The “soda can” is the foundation for the rest of our body to move from. If you have a dent in the can from your posture, you’ve lost your base of support and inherent strength from moving efficiently.

Push Cross Pull Push

One exercise I use to activate the tonic muscles of the core is Push Cross Pull Push. Lie on your back with a pillow under your head and bring your knees to your chest. (See Image)


Place the palms of your hands on the top of your knees (just above the knee caps) with your fingers pointed towards the ceiling. Get into a ball by lifting your tail bone and then push up on your knees. Resist this motion, staying in the ball position. Hold for 30–45 seconds. Then relax by hugging your knees to your chest.


Now cross your hands and place them on the inside of the opposite knee. Get into a ball by lifting your tail bone and push up on your knees. Hold in a ball position for 30 seconds.


Place your hands below your knees, lift your tailbone and pull up on your knees. This is similar to how you perform cannonball in a swimming pool, resist extension of your legs. Hold for 30 seconds.


Place your hands above the knees and press up towards the ceiling like you did for the first round. Hold here 30 sec.

In less than 2 min, you will gain a better understanding of what the muscles in the core feel like. You can then follow up with your favorite core exercises like planks, side lying planks, or bridges, etc. You want a stable body with these exercises and then move your arms or legs.


By redefining your understanding of what the core and good posture is, you can make the first steps towards moving efficiently. While the treatment of back pain and other injuries is always multifactorial, this understanding is crucial to reduce recurrence. Giving up the self-image of what we think makes a body look good (tight abs and a good butt) is often the hardest step.

This article was re-written from Melissa's "Ask the Expert" article published in Mammoth Times in 2021.

25 views0 comments

Recent Posts

See All


bottom of page