Intra-Abdominal Pressure and Trunk Rigidity

On several occasions, while trying to cultivate answers in terms of what constitute valuable lessons for our interns, I’ve gotten (among others) one common response. This is the importance of how to breathe in order to stabilize the trunk/torso while lifting heavy. If we are not actively teaching our athletes how to utilize intra-abdominal pressure and stabilize the trunk, we are not allowing them to get the most out of their training. This is important from both from a performance perspective, as well as a proactive approach to protecting them from injury.

First of all, what is intra-abdominal pressure and why is it important for performance?

IAP model

Intra-abdominal pressure is a mechanism which makes the trunk (and therefore spine,) more rigid and better suited to handle heavy loads. This is important in terms of force transference from the musculature driving the movement, as well as the safety of the athlete in terms of keeping the spine locked into a neutral position.

Look at the picture below, Kendrick Farris has just cleaned 205kg (~450lbs) and needs to stand up in order to attempt the second part of this lift. His legs are providing the driving force in order to stand up, and the barbell provides the external load. In order for the force of his legs to contribute maximally to standing up, he has to keep a rigid torso (and therefore spine,) in order to allow the maximum amount of lower body effort to displacing the barbell upwards (standing up.) If he were soft with the abdominals, and not creating intra-abdominal pressure, his trunk would collapse even if the legs were providing adequate force. This would result in both a missed lift, and in worse cases (likely if the bar were on the back) a flexed and collapsed spine.


Kendrick Farris catching a 205kg Clean.

car crusher

Imagine the lower half of the car crusher being the legs driving up, and the upper half of the car crusher being the barbell. Without adequate force in between to resist the two forces, the opposing forces will eventually meet and crush everything in between.

If you can stomach the analogy, imagine the car between the two surfaces were the trunk and spine. A strong enough spine (or car in this case) would be capable of withstanding and overcoming the pressure created by the two approximating surfaces.

If the lower part of the car crusher moved upwards (legs producing force,) and the car (spine/trunk) was rigid enough, it would actually move the top part of the car crusher (barbell) upwards. Of course this is all hypothetical, but let’s pretend it’s possible.

Hopefully it illustrates how a strong and rigid torso/spine can help transfer the force of the driving muscles to the external resistance.

farris springs

Which of these springs would you rather replace the red box with? I hope the left one. It’s thickness, rigidity, and strength would allow a greater force transference between the legs (driver) and resistance (barbell.)

How is intra-abdominal pressure created?

#1. It all starts with the diaphragm: Breathing deep into the diaphragm (where you feel the stomach and sides of the lowest ribs move out,) creates a low pressure system in the lungs. Simultaneous concentric contraction of the diaphragm and pelvic floor muscles combines with eccentric contractions of the abdominal musculature.



I took the above picture from this article in the Journal of Bodywork and Movement Therapies. The last line of the text says “Under ideal conditions, this activity is in balance with the spinal extensors.” It’s worth adding that in ideal circumstances, this will also happen as an anticipatory response (in varying degrees) to external stimulus or movement tasks. That is, creation of IAP and abdominal contraction will occur to some degree whenever we are about to move.

#2. Coactivation of the abdominal musculature: When the deep transversely (mostly) oriented fibers of the transverse abdominis, anterior-superiorly oriented fibers of the internal obliques, anterior-inferiorly oriented fibers of the obliques, and longitudinally oriented fibers of the rectus abdominis all fire together, they contribute to net stabilization of the spine.


Although boring, here is a picture of abdominal musculature which concerns us in this context.

#3. Extensor activation of the spine: While the abdominal musculature creates a flexion moment on the spine (basically pulling the spine into a rounded posture,) the spinal extensors work to create an equally strong extensor moment on the spine. When the forces work together antagonistically, they will hopefully produce roughly a net force of zero which keeps the spine statically erect in a neutral position.


Spinal Extensors: In this case, we are primarily concerned with the larger, more superficial extensors. Including: Iliocostalis Lumborum and Thoracis, Spinalis Thoracis and Lumborum (not listed,) Quadratus Lumborum, and Longissimus Thoracis. Generally, large paraspinal muscles.

#4. Understanding what a neutral spine is, and why it’s important:

Firstly, understand the spine as a series of primary and secondary curves.


Primary curves are those with a predisposition to being relatively kyphotic in nature. Secondary curves are those with a predisposition to being relatively lordotic in nature.

With alternating curvatures, the spine works in an alternating fashion. For example, an excessive extension in the cervical spine will cause an excessive lordotic curvature in the lumbar segments. Similarly an excessively kyphotic curve in the thoracic spine will cause a concomitantly kyphotic curve in the sacral/coccygeal segments, or posterior pelvic tilt. Janda illustrates this well with a cogwheel mechanism.

cog spine

In this illustration, the cogwheels work in alternating fashion. As described, the alternating curvatures affect each other and cause increased extensions or flexions in corresponding segments.

In a best case scenario, the spine will still have an alternating pattern of relatively lordotic and kyphotic curves, but they will not be terribly exaggerated. With this in mind, I don’t like to see athletes squat with their eyes on the ceiling or RDL with their eyes straight forward. The reason for this, is that I don’t like the excessive extension in the lower back. Relative extension, yes. Excessive extension, no. It may sound like I’m splitting hairs, but it’s a very simple correction, and will create a far more neutral spine with coactivation of the flexors and extensors.

Additionally, your spine is not designed to flex, extend, laterally flex, or rotate under large external load. Keeping it braced and neutral, is what our “core” is designed to do.

What happens if we don’t use diaphragmatic breathing and intra-abdominal pressure?

This article from the Journal of Osteopathic & Sports Physical Therapy suggests that folks who don’t breathe diaphragmatically as part of their habitual respiration experience chronic low back pain. Now, one of the arguments raised is: Are these “symptoms” causative or resultant? Does the diaphragm not move far enough to prevent low back pain, or does the low back pain cause the diaphragm to move less?

diaphragm excursion

A compelling image from the study which displays diaphragmatic excursion in A) Healthy patients without low back pain, and B) Patients with chronic low back pain.

An interesting point of this article is that the ventral spinal attachments of the diaphragm may pull and actually create an excessive flexion moment on some of the spinal segments creating a shearing force on the adjacent segments. This is because in the uncontracted (resting) diaphragm there is an increased angle between the medial and posterior segments of the diaphragm which gives it a more direct and efficient line of pull on the ventral aspect of the spine.

From this, we can deduce that improper or suboptimal diaphragmatic excursion can cause low back pain. If the diaphragm undergoes a path of suboptimal excursion (doesn’t travel far enough caudally/inferiorly,) the moment arm which creates the shearing force in the spinal segments is given mechanical advantage and can cause issues.

In fact, the opposite of diaphragmatic breathing is “chest-breathing.” This is commonly characterized by the in-breath taking longer than the outbreath. Also known as shallow breathing, this occurs when the diaphragm does not move caudally as shown in the left picture (A) above, and as a result, the person only inspires to fill a portion of their lung capacity. Consider for a second that oxygen only accounts for about 21% of the actual air we breathe in. In this case, the amount of oxygen taken in is far less than the carbon dioxide we expel. With the increase of carbon dioxide, the body takes on a more acidic pH level. As a result, these people tend to become chronically stressed and hypertensive.

Quick tip for athletes who want to improve performance on repeat-effort conditioning tests: Breathe diaphragmatically, you’ll recover more quickly and be able to give a better performance on the next rep. By breathing deeply, you’ll encourage your body to undergo a more parasympathetic nervous system shift, and recover for a better repeat effort.

In summary, I hope I’ve done a decent job in describing the benefits as well as mechanisms of diaphragmatic breathing and creating intra-abdominal pressure. Additionally, I feel that we (as coaches) aren’t spending enough time educating student-athletes on how to create these scenarios and take advantage of the benefits.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s