Posture guide
Rib flare is when the lower ribs at the front stick out more than the chest above or the tummy below, on one side or both. It isn't a medical diagnosis, and no study has measured how common it is. What is known: women's ribs slope more steeply than men's, the lower rib cage widens in pregnancy, and doctors describe lower ribs that flare on their own, with no other chest problem.
No study has shown that rib flare comes from weak abs, or that breathing exercises pull the ribs back in, though strength and breathing work can help you feel and move better. Ribs that stick out on one side, with a hump when you bend forward, should be checked for scoliosis, and a sunken or pushed-out breastbone by a GP.
This guide covers what's known about rib cage shape, pregnancy and children, the moves that help with 3D demos, and when to get checked.
Rib flare means lower ribs at the front that stick out more than the chest above or the tummy below, on one side or both. No study has measured how common it is. In medicine the term mostly describes the lower ribs in chest wall conditions, and an X-ray measure in scoliosis.
Women's ribs slope more steeply than men's, the lower rib cage widens in pregnancy, and babies' ribs sit more horizontally until about age 2.
The tummy muscles pull the ribs down only when you breathe out hard. In pregnancy, when the lower ribs widen most, the breathing muscles keep their strength. We found no study linking the position of the lower ribs to tummy strength.
We found no trial measuring whether breathing or core exercises move the lower ribs. The best-known method, balloon breathing, is published as a clinical suggestion. Strength and breathing work can still help you feel and move better.
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Ribs that stick out on one side, with a hump when you bend forward, can be scoliosis, and a sunken or pushed-out breastbone is a difference in the chest wall. A GP can check both.
The lower edge of the rib cage at the front (the costal margin) looks prominent. People notice it lying down, arching the back, reaching overhead, after pregnancy or when they're lean.
Doctors use 'rib flare' or 'costal flaring' mostly for lower ribs that stick out alongside a sunken or pushed-out breastbone, on one side (typically the left) or both. A review notes that flaring can also appear on its own, with no other chest problem. Researchers have also started measuring a 'rib flare distance' on X-rays of teenagers with scoliosis.
The angle where the two sides of the lower rib cage meet under the breastbone is called the subcostal angle. It widens in pregnancy, from about 68.5 degrees early on to 103.5 degrees at the end.
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There's no validated home or clinic test for rib flare on its own, and the popular check that your thumbs along the lower ribs should form a right angle has no source we could find. A clinician looks at whether one side sticks out with a hump on bending forward (scoliosis), at the shape of the breastbone, at signs of rickets in a young child, and at breathing effort in a baby.
In 40 healthy adults, women had smaller rib cages for their height and more steeply sloping ribs than men. The authors suggest this shape suits the extra room needed in pregnancy.
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The lower rib cage widens: the angle under the breastbone goes from about 68.5 to 103.5 degrees, and the width and lower circumference of the rib cage are larger late in pregnancy than after the birth. In 18 women followed through pregnancy, the rib cage changed shape but not volume.
In 66 children, babies' ribs sat more horizontally and their chests were rounder. Most of the change towards the adult shape happened in the first 2 years.
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On a deep breath in, muscles between the ribs and in the neck lift the rib cage, and breathing out lets it settle. Only one study has measured how the ribs turn as you breathe in living people.
The edge of the rib cage is easier to see with less fat over it, and raising your arms or arching your back lifts the front of the rib cage (our editorial observation).
We found no study measuring how common rib flare is in healthy people, and no agreed definition outside chest wall and scoliosis research. A review of chest wall conditions describes flaring that appears on its own, with no other abnormality.
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The diaphragm is the main muscle for breathing in. The tummy muscles, with the inner muscles between the lower ribs, pull the rib cage down when you breathe out hard. In pregnancy, breathing-muscle strength stayed normal even though the chest wall changed shape, and the diaphragm's contact with the lower ribs increased.
As the bump grows, the tummy muscle fibres lengthen by up to 15%, which reduces the force they can produce. That's a reason to rebuild strength after the birth, not proof that rib flare comes from weak muscles.
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We found no trial measuring whether breathing or core exercises change rib position or the angle under the breastbone. Balloon breathing comes from a 2010 clinical suggestion: its authors proposed that breathing out against a balloon makes the tummy muscles pull the lower ribs down and in, but they didn't test it.
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A sunken breastbone (pectus excavatum) or a pushed-out one (pectus carinatum) affects about 1 in 100 children, and both are 3 to 5 times more common in boys. Rib flare is often seen with a sunken chest, and both shapes tend to become more obvious in the growth spurt. A review found 'no clear consensus' on what exercise does for them.
Ribs that stick out on one side, most obvious when bending forward, are a recognised sign of scoliosis, which most often starts between 10 and 15. The NHS says scoliosis isn't linked to bad posture, exercise or diet.
The lower rib cage is wider late in pregnancy than after the birth, so it narrows again. We found no study tracking how fully the angle under the breastbone returns.
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The two long tummy muscles often separate in pregnancy, usually by about 2 finger widths, and the NHS says the gap usually goes back to normal by the time your baby is 8 weeks old. In 300 first-time mothers in Norway, 60% had a gap 6 weeks after the birth, 45% at 6 months and 33% at 12 months. An NHS trust leaflet calls a gap of 1 to 2 finger widths usual.
In 175 first-time mothers, a weekly exercise class with daily pelvic floor training didn't reduce how many had a gap. A 2026 review of 9 trials (450 women) found exercise narrowed the gap by about 8 mm, without better function. Expect stronger muscles rather than a closed gap.
Pelvic floor and deep stomach exercises, standing tall, and avoiding sit-ups, planks, high-impact exercise, straining on the toilet and heavy lifting to start with. Check the gap regularly, and see a GP if it's still obvious 8 weeks after the birth. Our diastasis recti guide covers the check and the exercises.
Signs include the ribs sticking out on one side, a hump on one side of the back when bending forward, uneven shoulders, a shoulder or hip sticking out, leaning to one side, and clothes that don't fit well. The NHS says it's unlikely there's anything seriously wrong, but it's best to get it checked. NHS Lothian's guidance for GPs says no exercise will make scoliosis worse, and swimming may help. The scoliosis guide covers the rest.
With a sunken or pushed-out breastbone, the lower ribs may flare on one side, typically the left, or on both, and the chest can look lopsided. A GP can refer you to a specialist if the shape bothers you or comes with symptoms.
Babies' ribs sit more horizontally and their chests are rounder, which can look like flaring. Most of the change towards the adult shape happens by about age 2.
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A baby or child whose tummy sucks in under the ribs while they breathe fast or grunt is working hard to breathe. That's a reason to call 999, not rib flare.
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Rickets, usually from too little vitamin D or calcium, can show as bumps where the ribs meet the cartilage at the front (felt to the side of the nipple line), swollen wrists and ankles, and bowed legs. See a GP if you're worried.
Scoliosis most often starts between 10 and 15, and a pigeon chest usually appears in the growth spurt around puberty. A new one-sided rib bump or a change in chest shape in a teenager is worth a calm GP check. A chest wall difference that's obvious early in childhood may lead doctors to check for a connective tissue condition.
If your lower ribs stick out on both sides, nothing hurts and you have none of the warning signs below, there's no evidence that anything needs correcting: we found no study of rib flare on its own (our editorial reading). The moves below are for strength and comfort.
Dead bugs, 2 to 3 sets of 6 to 8 each side, or the easier heel taps; knee planks, 3 to 5 holds of 15 to 30 seconds; the half-kneeling Pallof press, 2 to 3 sets of 8 to 10 each side (our editorial starting points). After a birth, start with the side-lying tummy draw-in at the move page's dose, which is the NHS's: hold for up to 10 seconds, up to 10 times.
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Lateral breathing (5 to 8 breaths at the start of every session), crocodile breathing (5 minutes of easy nose breathing, about 4 seconds in and 6 out) and slow breathing (at least 5 minutes, done regularly), all at their move pages' doses. A long, unhurried breath out is a comfortable cue, but none of this has been shown to change rib shape.
For ribs that flare mainly when you reach overhead: band rows at the move page's dose (3 sets of 10 to 15), foam roller thoracic extension at the move page's dose (5 to 8 slow breaths at each of 3 or 4 spots) and wall angels, 8 slow slides (editorial). Clear the foam roller first if you have osteoporosis.
Pelvic floor exercises at the move page's dose (start with 8 slow holds of up to 10 seconds and 8 quick squeezes, three times a day), the side-lying draw-in, and heel slides at the move page's dose (10 slow repetitions each side, once or twice a day), which are also in an NHS trust leaflet. Avoid sit-ups, planks and high-impact exercise to start with, as the NHS advises.
Braces for a pigeon chest are usually worn for at least 20 hours a day, and specialist clinics use a suction device (a vacuum bell) for a sunken chest. A review found no clear consensus on exercise, so use it for strength and posture, and leave the chest shape to a specialist.
The move page's dose: 5 to 8 breaths at the start of every session; no trial has tested this breath on its own. Stop and breathe normally if you feel dizzy or light-headed.
See the movement on the 3D figure: Lateral breathing (Pilates breathing)
At the move pages' doses, for comfort and relaxation. None of these has been shown to change rib shape.
Two or three times a week, at the doses above. In the early weeks after a birth, start with the draw-in, pelvic floor and heel slides, and leave planks until later, as the NHS advises.
3D demoDead bugBeginner · No equipment
3D demoDead bug heel tapsBeginner · No equipment
3D demoSide-lying tummy draw-inBeginner · No equipment
3D demoPelvic floor exercise (Kegel)Beginner · No equipment
3D demoSupine heel slideBeginner · No equipment
3D demoKnee plankBeginner · No equipment
3D demoHalf-kneeling Pallof pressBeginner · A band + An anchor pointBand rows and the foam roller at their move pages' doses; wall angels, 8 slow slides, keeping your lower back's gentle curve (editorial).
For comfort and strength: none of these is a rib flare fix. After a birth, the postnatal and pelvic floor routines come first.
A 6-minute breathing routine: slow breathing, crocodile breathing, alternate nostril breathing, box breathing and 4-7-8 breathing.
6 minBeginner5 movesNo equipmentA 15-minute beginner core workout on the floor: dead bugs, bird dogs, knee planks, side planks and curl-ups.
15 minBeginner6 movesNo equipmentA gentle 25-minute routine for the first weeks after birth: pelvic floor, breathing, tummy and hip exercises on the floor, sit-to-stands and a walk.
25 minBeginner12 movesA bench or box, Cardio machineA 5-minute daily pelvic floor workout for women and men: slow holds and quick squeezes, three times a day, with how to find the right muscles.
5 minBeginner2 movesNo equipmentA 25-minute low-load routine for hypermobile joints: hip, trunk and shoulder control plus balance, done slowly in the middle of your range.
25 minBeginner15 movesA bench or box, A wallA 12-minute routine for a stiff upper back and rounded shoulders: chin tucks, wall angels, Y-T-W raises and open books.
12 minBeginner8 movesA foam roller, A wallThis is effortful breathing, not rib flare.
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Get it checked if you notice:
A sunken or pushed-out breastbone, especially one that's getting more obvious in a growth spurt, or that comes with breathlessness, chest pain or tiring quickly on exercise.
A tummy gap that's still obvious 8 weeks after the birth: see a GP, who can refer you to a physiotherapist. An NHS trust leaflet suggests seeing a physiotherapist for a gap wider than 2 finger widths with a visible bulge.
Bowed legs, swollen painful wrists, pain in the back, ribs, pelvis or legs, or not wanting to walk much: see a GP, who can check for rickets.
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Pain where the ribs join the breastbone, difficulty expanding your chest on a deep breath, and back stiffness that's worse in the morning can be ankylosing spondylitis. See a GP.
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Our rib pain guide covers painful, clicking or moving lower ribs, and when they need urgent help.
We found no study showing it. Rib cages differ between women and men and widen in pregnancy, breathing-muscle strength stays normal in pregnancy, and the tummy muscles pull the ribs down only when you breathe out hard.
We found no trial measuring it. Balloon breathing comes from a clinical suggestion built on theory. Breathing practice can feel good, but it isn't a proven way to change rib shape.
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Ribs that stick out on one side with a hump on bending forward can be scoliosis, which isn't caused by posture, and a sunken or pushed-out breastbone is a difference in the chest wall.
In pregnancy, when the lower ribs widen most, the breathing muscles keep their strength and the diaphragm's contact with the lower ribs increases. We found no study showing harm from rib flare on its own.
The NHS advises avoiding sit-ups and planks at first, and trials haven't shown that exercise closes the gap, though it does build strength.
It's when the lower ribs at the front stick out more than the chest above or the tummy below, on one side or both. It isn't a medical diagnosis. Doctors use the term mostly for the lower ribs in chest wall conditions, and in scoliosis research.
Nobody has measured how common it is. Rib cages do differ: women's ribs slope more steeply than men's, the lower rib cage widens in pregnancy, and doctors describe lower ribs that flare on their own with no other chest problem. If both sides look alike, nothing hurts and you have none of the warning signs, there's no evidence it needs correcting.
It can come from the shape of your rib cage, and pregnancy widens the lower ribs. It can also come with a chest wall difference (a sunken or pushed-out breastbone), scoliosis (ribs sticking out on one side) or, in young children, rickets. Nobody has measured how often each applies.
We found no study showing that. The tummy muscles pull the ribs down only when you breathe out hard, and in pregnancy, when the lower ribs widen most, the breathing muscles keep their strength. Strong tummy muscles are worth having, but they haven't been shown to reshape the ribs.
We found no trial testing it. The best-known method, balloon breathing, is a clinical suggestion rather than a tested treatment. Exercise builds trunk strength and control, and breathing practice can help you relax, but neither is a proven way to change rib shape.
A sunken or pushed-out breastbone can make the lower ribs flare on one side, typically the left. If the ribs stick out on one side with a hump when you bend forward, or your shoulders or waist look uneven, see a GP to check for scoliosis. The NHS says it's unlikely to be anything serious, but it's best to get it checked.
The lower rib cage is wider late in pregnancy than after the birth, so it narrows again, but we found no study tracking how fully it returns. A gap between the tummy muscles usually goes back to normal by 8 weeks; see a GP if it's still obvious then.
Both are common after pregnancy, and the tummy gap can run up towards the ribs. In one study of first-time mothers, 60% had a gap 6 weeks after the birth and 33% at 12 months. Our diastasis recti guide covers the check and the exercises.
Rib flare on its own hasn't been shown to cause pain. Painful or clicking lower ribs, or pain where the ribs meet the breastbone, have other causes, which our rib pain guide covers. In a young adult, chest-wall pain with morning back stiffness can be ankylosing spondylitis, so see a GP.
No, but they often come together: rib flare is often seen with a sunken chest. Chest wall differences like this affect about 1 in 100 children and often become more obvious in the growth spurt. A GP can refer you if the shape bothers you, or if you get breathless or have chest pain.
Babies' ribs sit more horizontally and their chests are rounder until about age 2, which can look like flaring. A baby whose tummy sucks in under the ribs while breathing fast or grunting needs 999. Bowed legs or swollen wrists need a GP check for rickets.
Surgeons sometimes correct lower-rib flaring as part of an operation for a sunken chest. For a pigeon chest, specialist clinics use braces worn for at least 20 hours a day. A GP can refer you if the shape of your chest bothers you.
Exercise education, not a diagnosis or treatment plan, and clinical review of these guides is pending. Get a curve or hunch that is new or getting worse checked, above all in a growing child or after a fall, and get urgent help for numbness or weakness in the legs or a change in bladder or bowel control. Health disclaimer.
