Why Sucking In Is Dysfunctional, and What Real Core Bracing Looks Like
- Sonya Brotherton
- May 3
- 7 min read
I used to hold my stomach in to look skinny.
Standing in the supermarket queue. Sitting at my desk. Walking the dog. Riding and yard work. A constant low-grade clench across the front of the abdomen, because somewhere along the way I had absorbed the message that a flat stomach was the goal, and the way to get one was to pull it in.
What I now know, after years of strength and conditioning training and working with riders and athletes on how their bodies actually produce force, is that the suck-in habit is not just aesthetic theatre. It compromises the way you breathe, the way you brace, and the way you transfer force through your trunk. The very thing people are doing to look strong is the thing that is stopping them training, riding, and performing well.
This article covers what is mechanically going wrong with the suck-in pattern, why it shows up as the two rib flares I see all the time, and what proper bracing actually looks like.
What the rectus abdominis can and cannot do
The rectus abdominis is the six-pack muscle. It runs vertically from the pubic bone up to the cartilage of ribs five through seven and the xiphoid process at the base of the sternum. It is a sagittal plane flexor. That means its only job is to bring your ribs and pelvis closer together in the front of the body. Think of a sit-up.
What it cannot do is compress the abdomen from front to back. It cannot pull your waist in. It cannot manage the pressure inside your trunk. Those are different jobs handled by different muscles.
So when someone follows the cue “zip your pubic bone up to your sternum”, or simply tenses their six-pack to look firm, they are shortening the front of the body and creating surface tension. They are not building a cylinder of pressure. The aesthetic looks tight. The function is not there.
The two rib flares
There are two rib flare patterns I see repeatedly, and they have different mechanical causes.
Lordotic flare. The pelvis tips forward (anterior pelvic tilt), the lower back arches, and the ribcage tips up and back to balance the head over the body. The diaphragm and pelvic floor stop being parallel to each other, so they can no longer pressurise against each other. This is the classic stuck-in-extension posture.
Rectus-gripping flare. This one is less obvious but extremely common. When the rectus dominates and the obliques and transverse abdominis stay quiet, the lower ribs lose their lateral support. Ribs eight to ten are floating ribs connected only by cartilage. They are positioned by the obliques and transverse abdominis wrapping around the side of the trunk, not by rectus. Grip the front hard enough and the lower lateral ribs splay outward, because nothing is holding them in. You also tend to get a visible indent below the ribs from a chronically shortened upper abdomen.
Both patterns lift the lower ribs away from the diaphragm. Both compromise the same downstream function.
The canister model of the deep core
A working trunk is a closed cylinder. The diaphragm forms the lid at the top. The pelvic floor forms the base. The transverse abdominis (TVA) and obliques wrap the walls. The rectus is on the front of the wall, but it is not the wall itself.
When you breathe in, the diaphragm descends, the abdominal contents displace in all directions evenly, and the pelvic floor lengthens slightly to absorb the change in pressure. When you breathe out or brace under load, the pelvic floor recoils, the TVA draws inward like a corset tightening, and the diaphragm lifts. Pressure is generated concentrically, from the inside out. The cylinder pressurises like a tin of fizzy drink.
The deep core canister: diaphragm, transverse abdominis and obliques, pelvic floor.
This is where 360 breathing comes in. A functional inhale should expand the trunk in three directions: anterior (the belly comes forward), lateral (the lower ribs widen, what is called bucket-handle motion), and posterior (you can feel the back of the lower ribs press against your hands, or against the wall behind you). If your breath only goes into the front of the belly, or only into the upper chest, you are missing the cylinder.
The Zone of Apposition and why rib flare is a problem
The diaphragm is dome-shaped at rest. The lower edge of the dome sits parallel to the inside wall of the lower ribcage in a cylindrical region called the Zone of Apposition (often shortened to ZOA). This is the area where the diaphragm does its mechanical work as a breathing muscle.
When the lower ribs flare up and out, the dome flattens and the ZOA shrinks. The diaphragm now has less excursion (range of movement) and less mechanical leverage. It stops being primarily a breathing muscle and starts being a postural one. The body then recruits the scalenes, sternocleidomastoid, pec minor, and upper trapezius to drive ventilation. This is metabolically expensive, fatigues quickly, and chronically loads the neck and shoulder girdle.
That is the chain that links a chronically held-in stomach to neck pain, jaw tension, and breathlessness on exertion.
How the ribs are meant to move
Healthy breathing requires the ribs to move. There are two motions worth knowing.
Pump-handle motion happens at the upper ribs (one through five) in the sagittal plane. The front end of the rib lifts forward and up on inhale, like the handle of an old water pump. This increases the front-to-back diameter of the chest.
Bucket-handle motion happens at the lower ribs (six through ten) in the frontal plane. The side of the rib lifts up and out on inhale, like lifting the handle of a bucket. This increases the side-to-side diameter of the chest.
Pump-handle (upper ribs) and bucket-handle (lower ribs) motion on a healthy inhale.
If your lower ribs are already flared at rest, they are stuck near the end of their bucket-handle range. There is nowhere for them to go on inhale. Tidal volume (the amount of air moved with each breath) is reduced. The ability to ramp up ventilation when training is significantly compromised. You will feel out of breath sooner than you should, even when you are fit.
What proper bracing actually looks like
The brace that works under load is not a suck-in, and it is not a six-pack squeeze. It is the canister pressurising.
Stack the ribs over the pelvis. Both should be roughly level rather than tipped forward or back. Breathe in 360 degrees, expanding into the front, sides, and back of the lower ribs. Then either brace against the inhaled pressure (the Valsalva-style brace used in heavy lifting), or exhale through pursed lips while drawing the TVA inward and lifting the pelvic floor (the brace used for endurance work and for pregnancy and postnatal training).
Done correctly, the rectus will feel firm without scrunching. The waist will not pull inward; it will widen slightly as pressure pushes outward against the abdominal wall. The ribs stay set down over the pelvis. The neck and jaw stay quiet, because the diaphragm is doing its own job.
This is the brace that protects your spine when you lift, stabilises your trunk when riding, and lets you breathe at the same time.
How sucking in compromises athletic breathing
Bringing this together, here is what chronic sucking in and rectus-gripping cost the athlete:
• The Zone of Apposition shrinks, so the diaphragm cannot generate adequate pressure or excursion.
• Rib motion is restricted, so tidal volume drops and ventilation cannot scale with effort.
• Accessory neck and shoulder muscles take over breathing, fatiguing fast and causing chronic tension.
• Intra-abdominal pressure cannot build properly, so force transfer through the trunk is weak.
• Pelvic floor co-activation is disrupted, which is a primary driver of stress urinary incontinence in active women.
• The system runs in low-grade sympathetic activation, so heart rate variability drops and recovery slows.
It is also worth knowing that rectus tension during effort actively inhibits the diaphragm. This is one of the mechanisms behind exercise-induced side stitches. The diaphragm cannot move freely against a tense anterior wall, so it cramps.
Other consequences worth flagging
Beyond performance, chronic sucking in is associated with a list of well-documented issues:
• Stress urinary incontinence.
• Increased risk of pelvic organ prolapse.
• Aggravation of diastasis recti.
• Worsening of reflux and hiatal hernia symptoms.
• Hypertonic (over-tight) pelvic floor.
• Neck and jaw pain, headaches, and TMJ-related issues.
• Constipation. The diaphragm normally massages the abdominal organs with each breath; if it is not moving, that gentle motility input is lost.
• Disrupted sleep, through chronically elevated sympathetic tone.
If any of those apply to you, that is a conversation for your GP or a pelvic health physiotherapist, not something I can or should diagnose. What I can tell you is that learning to breathe and brace properly is foundational to almost everything else we do.
The takeaway
Holding your stomach in to look flat is not a neutral habit. It restructures how you breathe, how you brace, how you train, and how your nervous system sits at rest. The flat-but-tight aesthetic that people are chasing is, mechanically, a less functional body, not a stronger one.
Build the canister. Restore the breath. Let the surface tension go. The body that follows is the one you actually wanted in the first place.
References
Bordoni, B. and Zanier, E. (2013) ‘Anatomic connections of the diaphragm: influence of respiration on the body system’, Journal of Multidisciplinary Healthcare, 6, pp. 281-291.
Boyle, K.L., Olinick, J. and Lewis, C. (2010) ‘The value of blowing up a balloon’, North American Journal of Sports Physical Therapy, 5(3), pp. 179-188.
De Troyer, A. and Boriek, A.M. (2011) ‘Mechanics of the respiratory muscles’, Comprehensive Physiology, 1(3), pp. 1273-1300.
De Troyer, A. and Estenne, M. (1988) ‘Functional anatomy of the respiratory muscles’, Clinics in Chest Medicine, 9(2), pp. 175-193.
Hodges, P.W. and Gandevia, S.C. (2000) ‘Activation of the human diaphragm during a repetitive postural task’, Journal of Physiology, 522(1), pp. 165-175.
Hodges, P.W. and Richardson, C.A. (1996) ‘Inefficient muscular stabilization of the lumbar spine associated with low back pain’, Spine, 21(22), pp. 2640-2650.
Hruska, R.J. (1997) ‘Influences of dysfunctional respiratory mechanics on orofacial pain’, Dental Clinics of North America, 41(2), pp. 211-227.
Kolar, P. et al. (2010) ‘Stabilizing function of the diaphragm: dynamic MRI and synchronized spirometric assessment’, Journal of Applied Physiology, 109(4), pp. 1064-1071.
Kolar, P. et al. (2012) ‘Postural function of the diaphragm in persons with and without chronic low back pain’, Journal of Orthopaedic and Sports Physical Therapy, 42(4), pp. 352-362.
Sapsford, R.R. and Hodges, P.W. (2001) ‘Contraction of the pelvic floor muscles during abdominal maneuvers’, Archives of Physical Medicine and Rehabilitation, 82(8), pp. 1081-1088.
Sapsford, R.R. et al. (2001) ‘Co-activation of the abdominal and pelvic floor muscles during voluntary exercises’, Neurourology and Urodynamics, 20(1), pp. 31-42.
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