During an inhale, the diaphragm descends into the abdomen, pushing on everything below it (guts, etc.) just as a balloon stretches down and out. The abdominal muscles, back muscles, pelvic floor, connective tissue, and skin expand to accommodate the “inflated” abdomen and pressure builds. Most breaths will just be released at rest, allowing the pressure in the abdomen (IAP) to decrease slowly on the exhale with some muscular tension helping expel air out. Juile Wiebe describes this pressure-tension mechanism as “piston breathing” and is a great resource for more info. However when our “core” muscles go to work, tension primarily from the abs surrounds the expanding core in one or more planes. This tension creates an opportunity to build and capitalize on IAP. This, friends, is the true heart of the core, or I guess core of the core.
“Brace your abs,” “tighten your core,” “squeeze belly button to spine,” and so on are semi-vague cues you will hear being directed toward core-strengthening clients in both fitness and rehab settings. The importance of having a “strong” core has been boiled down to these sound bytes and as a result, many people walk around subconsciously gripping their abs or maybe holding tension in their back. What’s more, there are a lot of people who cue themselves into walking around all day every day consciously creating unrelenting tension in their midsection. Creating tension throughout the abdominal and lumbar musculature is normal and undoubtedly necessary, however it must be able to coordinate and cooperate with a pressure mechanism, otherwise known as breathing—the real key to effective, efficient core function.
Imagine the balloon inside of your abdomen, occupying everything between the bottom of your rib cage and the bottom of the pelvis. What would happen if this balloon was cinched across the middle by a belt around your belly button? What would happen to your breathing? What about the pressure inside your abdomen or the muscular tension of your abdominals? This is what many people are effectively doing by sucking in, holding belly button to spine, or otherwise incorrectly executing core function. Here are a few possible consequences:
1. Shallow chest breathing might occur because pressure does not move into the cinched, blocked abdominal zone.
2. Assuming the “belt” is actually abdominal muscle “gripping,” the abs no longer lengthen and shorten (only stay locked in place) making them poor at dynamic stability and weaker in other positions besides “braced.”
3. If this were actually a belt (weight lifting, tight pants, “waist trainer”—insert eye roll here) then some pressure in the abdomen would occur from the outside diminishing the force production of your abs—your built in belt—resulting in weaker muscles because they were relying on another option.
4. Excessive downward force may be placed on the pelvic floor imposing more demand on the muscles, but limiting their ability to shorten and contract in response.
So what should happen? Once ab muscles are contracted, the key is to continue to allow them to expand during inhales. Because the muscles are working while lengthening, this is what is called an eccentric contraction (like lowering a dumbbell back down after curling it up) and the lengthened position of the core muscles prepares them to be able to better create a concentric contraction, or shortening while working. Keep in mind that the actual amount of length change is not that great, so the bigger benefit here is really derived from what is happening underneath.
With abs engaged and eccentrically loading upon an inhale, the amount of intra-abdominal pressure created is much more than the pressure built during a relaxed inhale. The abdominal wall actively restraining the amount of fill into the abdomen (but remember it is still eccentrically loading) is acting like an elastic vice around the balloon, increasing the pressure of the contents within. By marrying together the intra-abdominal pressure with the active contraction of the surrounding core musculature, the effect is an incredible amount of trunk stability and a relative “stiffening” of the spine that is the basis on which all other movements build off of. Bold statement, I know. Let me elaborate.
Have you ever been in a bounce house? Stepped onto a beach what seems like miles from the water and had to trek through loose (burning hot) sand? When the floor beneath you has some give to it, the amount of work you must do to move around on top of it escalates quite a bit. In the same way, if your trunk cannot create sufficient stability—remember proximal stability enables distal mobility—your body will have to work much harder to react to the forces it is exposed to as well as the ones you yourself create. Walking on an unstable surface might feel like a more challenging workout, which might be nice, but there isn’t an advantage to moving around during every day motions exerting more work. In fact, quite the opposite. Doing extra work doesn’t get you bonus points, it is inefficient and can get you injured.
Efficiency of movement refers to the amount of work required to complete a task. In more technical terms, it is a ratio of useful work to the energy expended. Who wants to do more useless work or expend more energy for same outcome? When a breakdown of core stability occurs, there will be an inevitable loss of movement efficiency and that is exactly what happens. While necessary to oversimplify, but impossible to understate, IAP is the key to creating efficient movement no matter how big or small.
For something small such as opening a door, you need a minimal amount of intra-abdominal pressure to provide a stable anchor for your arm to connect to as it pushes or pulls. On the other hand, for a high demand task like maxing out your bench press, you need to create an enormous amount of IAP to stabilize the spine and help generate force during the lift--time when it would be appropriate to hold the breath until the lift is complete. In short, whether you are exhibiting acts of chivalry or setting the RPS bench press record, intra-abdominal pressure shows up, and ideally in an amount proportional to the demand.
The above examples describe trunk stability during movements where the trunk position is relatively neutral and fixed, but this mechanism also occurs during activities where the spine must change shape, like running. During rotational activities (yes running requires rotation) the spine must be mobile enough to permit twisting, but stable enough to continue to perform efficient movement. Maintaining abdominal fill during inhales and forceful exhales to recruit abdominal tension and keep IAP up, but eliminating the fixed, braced position creates the ability to balance stiffness and movement, yielding an efficient movement.
Consider four types of breathing patterns and their associated IAP:
1. Resting breathing, IAP naturally building during the inhale.
2. Light working breathing, IAP naturally building during the inhale and elevating during a forceful exhale as abdominal musculature compresses the core.
