The abdominal hollowing technique has been touted as a way to improve your core stability and has been a universally accepted, go-to exercise for physical therapists (PTs) and fitness coaches for the last decade. Unfortunately, it has been shown that the technique in no way leads to a stable spine. In fact, abdominal hollowing does precisely the opposite and effectively ruins our spinal stability.
We have three layers of abdominal muscles. The outer layer is our rectus abdominis (think six-pack muscle), which runs vertically from our ribcage to our pelvis. In the middle, we have our external and internal obliques, which run diagonally from our lower ribcage to our pelvis. Finally, we have the transversus abdominis TrA, which runs horizontally beneath the other layers. Our muscles work as teams to not only create joint torque, but to also (and more importantly) maintain core stability. There is no single muscle responsible for this.
So instead of training muscles as a team and as they function in real life, hollowing aims to instead activate a single muscle in isolation. Research shows that hollowing will in fact produce increased activity in the TrA, but you are also causing a weakening of the external and internal oblique muscles. Drawing in the navel, or the act of “sucking in your gut as if you’re putting on a tight pair of jeans,” tends to detract the emphasis from the working muscles on most movements that we do in the gym, and it can lead to injury.
Yes, it is necessary to keep the core tight during exercise, but overemphasis on the transverse abdominis can negatively affect performance on movements such as squats and deadlifts.
It has been noted that the abdominal hollowing approach felt uncomfortable, almost as if one’s lungs were being pushed out of the throat while descending into a squat or deadlift. Dr. Stuart McGill, a spinal biomechanist points out that there is a clear distinction between abdominal bracing and hollowing.
Think about what you would do if you were to prepare yourself for someone to punch you in the gut. You would immediately tense and stiffen your core to brace for the impact. This is exactly what abdominal bracing is. In abdominal bracing, you are simultaneously co-activating all layers of core muscles, in addition to activating your lats, quadratus lumborum, and back extensors. This means the entire abdominal wall is activated from all angles, sides, and directions, causing the three layers of the muscles to actually physically bind together.
This binding enhances the stiffness and stability of the core to a much greater degree than what would otherwise be produced by the sum of each individual part. This is what McGill refers to as superstiffness. It is this stiffness that provides us with 360 degrees of spinal stability, making us injury resilient and helping us achieve optimal performance.
You see, stiffness is actually key for spinal stability and spine health. Having a stiff core eliminates micro-movements in the joints that lead to spine and tissue degeneration. Without stiffness, these micro-movements would gradually gnaw away on our nerves, eventually causing pain and even disability. Stiffness braces these micro-movements and takes away the pain, essentially building a spinal armor.
To visualize this a bit better, McGill gives the great example of a guy-wire system (like a ship mast). Think of the obliques and the rectus abdominis as the supporting guy wires of the spine. They will be more effective at stabilizing the spine when they have a wider base, as they do when the core is braced. On the other hand, when the abdomen is drawn in, or hollowed, there is a much narrower base of support leading to significantly less stability.
Another way to visualize this: if you want to increase core stability, do the opposite: push out your gut! This creates a very rigid torso. This intra-abdominal pressure (IAP) is what you want your core to feel like when you are stiffening your muscles during exercises.
If we teach abdominal hollowing for everyday tasks, we are essentially encouraging our rectus abdominis and oblique muscles to weaken and remain inactive. Furthermore, we are not allowing our core to maintain its stiffness, which means one unexpected bump, fall, or movement and we could be dealing with a significant back injury. Our bodies do not work in isolation, and we should not be training them as if they do.
When it comes to spinal stability all of our muscles work together and play an important role. These muscles must be balanced in order to be able to withstand large loads placed upon them to keep us injury free. Training single muscles leads to the exact opposite effect, instead causing an unstable, injury prone spine. This is why when training core stability, whether immediately following an injury or during athletic performance training, we should never focus on isolating a single muscle. Instead, bracing and the activation of our entire abdominal wall should be practiced.