Core Concepts: Part I

Core Concepts: Part I

The Key to Training Trunk Stability

By Josh Kruhm, CPT, USAW-1, WLS, PES

This will be a 3 part series focused on trunk strength and stability and its impact on human performance. The beginning of this 3 part series will be  focused on what stability is, the dynamics of trunk stability and how to properly brace your core. We will discuss the “core” (pun definitely intended) components of the trunk and why it is important to train for a stable trunk.

What is Stability?

First, we must understand what stability is and which muscles are key in trunk stability and their functions as a part of the whole. Stability is the ability to maintain a desired position (static stability) or movement (dynamic stability) despite motion, force, or control disturbances (1). The foundation or “keystone” of stabilization of the body is pressure within the abdomen, or as it is commonly called intra- abdominal pressure (IAP). This pressure stabilizes the spine, pelvis, and ribcage, creating a solid fixed point from which muscles can pull in order to create, control, or even prevent movement. The amount of pressure in the abdomen at any given moment is dependent on the stability requirements for the task being executed (2,3,4,5,6).

The major muscles involved include the pelvic floor muscles, transversus abdominis, multifidus, internal and external obliques, rectus abdominis, erector spinae (sacrospinalis) especially the longissimus thoracis, and the diaphragm (Fig. A).

While all of these muscles are very important when it comes to protecting our internal organs and the spine, for the sake of time I will only focus on a few at a time based on the movement(s) that they assist. This article, the first in this series, will focus a lot on the impact of the diaphragm. 

The Diaphragm

The diaphragm is a dome-shaped muscular partition separating the thorax from the abdomen in mammals (Fig. B). It plays a major role in breathing, as its contraction increases the volume of the thorax and so inflates the lungs.

From this you can gather that this muscle would be extremely important to exercise. Most people will try to breathe through their chest so to speak, but that only allows us to get so much oxygen. When we breathe the diaphragm contracts downward creating a vacuum which brings fresh air into the lungs. By becoming more effective at diaphragmatic breathing, we can breathe much more fully which is important when bracing. It is also critical in recovery. However, that is a different topic for a different day.

How does it work?

 So what does all of this have to do with trunk stability? Think of the diaphragm as an air bag in your car. When we inflate the diaphragm, it creates a cushion or “air bag” for the spine. So all of those spine compressing exercises that we love to do? By breathing through the diaphragm we can protect our spine so much more than the typical cue of “tighten your core”. Usually this cue, while activating our core, also creates a larger compressive force on our spine. Think of this method of bracing your core as trusses on a ships mast. Everything is pulled tight and secure, but there is a lot of compressive pressure on the mast (your spine). So to sum all of that up simply, diaphragmatic breathing/bracing=air bag for spine=good and “tighten your stomach/abs/core”= increased spinal compression=bad.


Below is a way to practice diaphragmatic breathing before you attempt to pull your 1rm deadlift or lift that super heavy rock out of your garden. 

1. Lie on the floor face up with knees slightly bent.

2. Place a small pillow under the head if that is more comfortable for you.

3. Place your hands lightly on your stomach.

4. Concentrate on breathing using the diaphragm, not using the chest, and feeling the stomach rise as the lungs fill from the bottom.

5. Let the stomach fall naturally when breathing out by relaxing the diaphragm.

6. Progress by placing a small weight on the stomach, such as a small book, and do it all again.

7. The next stage is to stand up and place your hands on your stomach again, feeling how you breathe. Surprisingly, you may find this step requires some concentration initially. (7)


Beginner Version
Advanced Version

These exercises are a good starting point for learning how to breathe and brace your core properly. If you want to learn more about diaphragmatic breathing or trunk stability, please contact us at: info@madlabperformance.com.

This article does not necessarily represent the views/opinions of MadLab Performance, LLC. This article is not meant to recommend health solutions in place of a doctor or other medical professional and should only be used to help those reading it gain more information prior to making their own decision.

Josh has experience with anything and everything, from prenatal and postpartum care to coaching high school athletes as they prepare for high-level DI careers. He specializes in getting the most out of whoever he is coaching. Josh is the Head Coach for MadLab Performance and manages the company’s personal trainers. He also is a frequent contributing writer for MadLab’s continuing education articles. Josh may be contacted by email at: josh@madlabperformance.com


1. Reeves, NP, Narendra, KS, and Cholewicki, J. Spine stability: The six blind men and the elephant. Clinical Biomechanics 22: 266- 274, 2007.

2. Hodges, PW, Eriksson, AE, Shirley, D, and Gandevia, SC. Intra- abdominal pressure increases stiffness of the lumbar spine. Journal of Biomechanics 38(9): 1873-1880, 2005.

3. Hodges, PW, and Richardson, CA. Relationship between limb movement speed and associated contraction of the trunk muscles. Ergonomics 40(11): 1220-1230, 1997.

4. Kolar, P, Sulc, J, Kyncl, M, Sanda, J, Cakrt, O, Andel, R, et al. Postural function of the diaphragm in persons with and without chronic low back pain. Journal of Orthopedic and Sports Physical Therapy 42(4): 352-362, 2012.

5. Kolar, P, Sulc, J, Kyncl, M, Sanda, J, Neuwirth, J, Bokarius, AV, et al. Stabilizing function of the diaphragm: Dynamic MRI and synchronized spirometric assessment. Journal of Applied Physiology 109(4): 1064-1071, 2010.

6. Hackett D, and Chow, C. The Valsalva maneuver: Its effect on intra-abdominal pressure and safety issues during resistance exercise. The Journal of Strength and Conditioning Research 27(8): 2338-2345, 2013.

7. Kidd, S. (2019) How to Activate Your Diaphragm to Improve Breathing and Performance. [online] Breaking Muscle. Available at: https://breakingmuscle.com/fitness/how-to-activate-your-diaphragm-to-improve-breathing-and-performance [Accessed 17 Jul. 2019].

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