The Body in ConversationPart 7: The Abdominal Wall - More Than a Corset
Part 7: The Abdominal Wall - More Than a Corset
If you have ever been told to:
“Pull your tummy in.”
“Engage your core.”
“Brace.”
“Switch on your deep abdominals.”
You could be absolutely forgiven for imagining that the abdominal wall has one solo job.
Tighten and be hard.
Preferably all day.
And so many of us do exactly that.
We grip, pull in, brace and hold our stomachs almost without realising it, and that can have a very real effect on how the rest of the body is able to move, breathe and respond. We’ll get into that a little later in this blog.
But the abdominal wall is far more than just a “wall” to tighten.
Perhaps the word wall is part of the problem.
It immediately takes us into the world of bricks, concrete, rigidity and being tough.
Some people, including me on occasions, have described the abdominal wall as a corset: something that opens around the body and gathers back in again.
But these days even that feels a little too restrictive an image for me.
I think of it more like the bell of a deep-sea jellyfish.
A jellyfish is soft, fluid and incredibly adaptable.
It doesn't have a rigid centre holding everything still.
Yet through coordinated changes in shape and tension, it can move, respond to the water around it and cope with continually changing pressure.
Soft doesn't mean inactive.
Movement doesn't mean unstable.
And strength doesn't have to mean rigid.
Instead of imagining the centre of your body as something that has to be clamped shut, imagine a living, responsive container whose shape is continually changing depending on what is happening inside it and around it.
That is much closer to the abdominal wall I am interested in.
And, just like the diaphragm, it is not working alone.
It is part of a team.
Lengthening.
Shortening.
Rotating.
Transferring force.
Responding to pressure.
Helping you cough, laugh, shout, lift, run and go to the toilet.
And its behaviour changes depending on what you are asking your body to do.
So perhaps the question isn't:
“Is my core switched on?”
Perhaps a better question is:
“Can my abdominal wall respond?”
First, what actually is the abdominal wall?
When we talk about “the abs”, most of us immediately picture the rectus abdominis.
The six-pack muscle.
And when we talk about the deeper abdominal muscles, transversus abdominis is often described as a belt wrapping around the waist.
That image can be useful.
But anatomically it is much bigger, richer and more connected than that.
Across the front and sides of the abdomen we have:
rectus abdominis
external oblique
internal oblique
transversus abdominis
and the connective tissues that link and transmit forces between them, including the rectus sheath and linea alba
And they are not four isolated strips of muscle stacked neatly on top of one another.
They overlap.
Their aponeuroses blend.
Now, if that word has lost you already, stay with me.
An aponeurosis is simply a broad, flat sheet of connective tissue. You can think of it a little like a wide, flattened tendon.
Rather than a muscle ending in one narrow tendon attaching into one small point, an aponeurosis allows muscle forces to spread over a much broader area and blend with other tissues.
So when we talk about the abdominal muscles, we are not only talking about muscle.
We are also talking about these great sheets of connective tissue running between them, wrapping around them and meeting one another.
Their muscular fibres run in different directions.
Some vertical.
Some diagonal.
Some more horizontal.
And their attachments link the ribs, spine, thoracolumbar fascia, pelvis and midline together.
The external oblique, the largest and most superficial of the flat abdominal muscles, attaches into the lower ribs above and the iliac crest and pelvis below, with its broad aponeurosis travelling towards the linea alba.
Underneath it sits the internal oblique, with fibres travelling in a different direction. It links the thoracolumbar fascia and iliac crest with the lower ribs, pubic region and linea alba.
Then we get to transversus abdominis.
And this one is particularly interesting.
It is often drawn as a neat horizontal belt wrapping around the waist.
But it doesn't simply begin at one side of your tummy and finish at the other.
Posteriorly, it has attachments into the thoracolumbar fascia.
And the thoracolumbar fascia is connective tissue too.
It is a large, layered connective tissue structure across the back of the trunk, associated with the spine, pelvis and many of the muscles of the back and abdominal wall.
So already our supposed little “belt” is communicating with the back of the body.
Superiorly, transversus attaches to the inner surfaces of the lower costal cartilages.
Inferiorly, it has attachments along the iliac crest and inguinal region.
And as its muscle fibres travel forwards, they become a broad aponeurosis which contributes to the rectus sheath and ultimately reaches the linea alba in the centre of the abdomen.
So rather than thinking of transversus as simply a belt, imagine something more like a broad muscular and connective tissue sheet stretching from the back of the body, around the sides and towards the midline, with attachments above and below connecting it into the ribcage and pelvis.
And right at its upper border something even more interesting happens.
The costal fibres of the diaphragm and transversus abdominis interdigitate along the inside of the lower ribs and costal margin.
Interdigitate is another fantastic anatomy word that basically means the fibres come together almost like interlocking fingers.
So the diaphragm and transversus are not living in two completely separate muscular worlds.
Their fibres actually meet around the lower ribcage.
I love this anatomically because suddenly the idea of the diaphragm and abdominal wall being in conversation becomes much less abstract.
They are literally meeting one another.
Then at the front we have the rectus abdominis, running vertically between the pubic region below and the xiphoid and lower costal cartilages above.
Again, it connects pelvis to ribcage.
But the rectus isn't simply sitting there by itself either.
Around it sits the rectus sheath.
The rectus sheath is predominantly connective tissue, created by the broad aponeuroses of the external oblique, internal oblique and transversus abdominis as they travel around the rectus muscles.
Those connective tissue sheets then meet and interweave at the midline to help form the linea alba.
And the linea alba is connective tissue too.
It isn't simply the white line that separates the two halves of your six-pack.
It is a strong, layered connective tissue meeting place running down the middle of the abdominal wall, where the aponeuroses coming from both sides interweave.
That means force can be transmitted through it from one side of the abdominal wall to the other.
So even the “six-pack” isn't really standing there on its own.
It is wrapped within, suspended within and connected into a much larger muscular and connective tissue system.
This is why I struggle when we isolate one muscle and give it one job.
“Transversus is your corset.”
“Rectus flexes the spine.”
“Obliques rotate you.”
Yes, those descriptions can help us learn anatomy.
But they are only the beginning.
In a living human, these tissues are physically connected and continually transferring and responding to forces between the ribs, spine, pelvis, abdominal wall and midline.
Which is another reason I think of the abdominal wall less as a collection of individual muscles…
and much more as one adaptable, interconnected muscular and connective tissue structure, with many different fibre directions and many different options.
Some vertical.
Some diagonal.
Some more transverse.
All capable of changing tension and shape depending on breathing, movement, posture and load.
Already, this should give us a clue.
This is not simply a belt designed to pull your stomach flat.
It is multidirectional.
Connected.
Adaptable.
And constantly changing.
And the diaphragm is sitting right above it
In the last few parts of this series we have followed the diaphragm down from the ribs, around its openings and into its relationships with the spine.
Then in Part 6 we looked at pressure.
Because when the diaphragm contracts and descends during an inhale, something has to happen to the contents below it.
They cannot simply disappear.
The abdominal contents shift and the pressure inside the abdominal cavity changes.
One of the visible consequences can be movement of the abdominal wall.
During quiet breathing, the descending diaphragm can contribute to an outward movement of the abdomen.
Notice what I said there.
Can contribute to.
Not:
“Your belly must push out.”
Breathing is three-dimensional.
The ribs move.
The abdominal wall changes shape.
The pelvic floor responds.
The spine, thorax, fascia, aponeuroses and linea alba are involved.
And the exact strategy will vary depending on whether you are lying down, standing, walking, running, talking, lifting a kettlebell or being chased by a humongous bear.
Hopefully that last one is by far the least common.
The abdominal wall has to be able to yield
This is one of the things I think we sometimes miss when we talk about core strength and function.
We become very interested in contraction.
But tissues also need to be able to lengthen, change shape and deform.
As the diaphragm descends during an inhale, the abdominal wall needs enough adaptability to accommodate the changing shape and pressure of the abdominal cavity.
That doesn't mean your tummy suddenly needs to become floppy.
In fact, I really dislike instructions such as:
“Just relax your belly.”
Because that can make it sound as though good function means switching everything off.
It doesn't.
The abdominal wall is not simply either on or off.
Its activity and tension are continually changing.
Sometimes it lengthens.
Sometimes it gathers.
Sometimes it has to become much firmer.
Sometimes it has to yield.
Think of a dimmer switch rather than a light switch.
And think about the difference between a brick wall and a trampoline.
A brick wall is certainly rigid.
But you probably wouldn't want to land on one.
A trampoline can accept load, change shape and then return energy.
For human movement, we generally need some version of that second quality.
Not motionless rigidity.
Adaptability.
What happens when the breath becomes paradoxical?
There is another breathing pattern that is particularly interesting here:
Normally, when you inhale, the diaphragm contracts and descends.
The lower ribcage expands and the abdominal wall usually has some capacity to move outwards as the abdominal contents are displaced.
In paradoxical breathing, that relationship changes.
The chest may expand as you inhale while the abdominal wall actually draws inwards.
Then on the exhale the opposite can happen, with the abdomen moving back out.
So instead of the ribcage and abdomen changing shape together in a reasonably coordinated way, they begin moving in opposing directions.
This is often described as thoraco-abdominal asynchrony - essentially, the chest and abdominal parts of the breathing system are no longer moving in sync.
And I think this is really useful to understand when we are talking about abdominal gripping.
If somebody has spent years being told to:
“Pull your tummy in.”
“Hold your core.”
“Keep everything tight.”
…the abdominal wall may become less available to change shape freely during breathing.
The body still has to breathe.
So it finds another way.
Sometimes that means more movement through the upper chest.
The sternum may lift.
The upper ribs may become much more dominant.
The neck and accessory breathing muscles may begin doing more work.
And in some people you can see the chest and abdomen begin to move in opposing directions.
That pattern is called paradoxical breathing.
Importantly, though, paradoxical breathing can also occur for other reasons.
A very pronounced abdominal paradox can be associated with diaphragm weakness, neurological conditions, airway obstruction or significant respiratory disease, so it is not something we should simply blame on somebody “holding their stomach in”.
But it does beautifully demonstrate something we have been talking about throughout this series:
breathing requires movement between compartments.
The diaphragm needs somewhere to descend.
The ribs need to be able to move.
The abdominal wall needs to be able to change shape.
The pelvic floor needs to respond to the changing pressure above it.
If one part of that system becomes very restricted, the rest of the body has to reorganise around it.
And the body is remarkably good at doing that.
It will find a way to keep you breathing.
But that doesn't necessarily mean it is using the most efficient strategy available.
Which brings us straight back to our abdominal wall.
We don't want it permanently floppy.
And we don't want it permanently braced.
We want it able to yield, gather, strengthen and change shape depending on what the breath and the movement require.
Once again we are looking for - options.
Then the conversation reverses
As we breathe out, the diaphragm relaxes and returns upwards.
At rest, much of normal expiration happens through elastic recoil rather than because you consciously squeeze your abdominal muscles.
But as the demands of breathing increase, the abdominal muscles can become much more involved.
Run up a hill.
Blow up a balloon.
Cough.
Sing loudly.
Lift something heavy.
Now the abdominal wall may contribute much more actively to breathing and pressure generation.
And this is where it gets really super interesting.
Because the muscles don't simply switch on together like four lights connected to one switch.
Your brain is already one step ahead of you
Have you ever wondered how your body manages to stay upright while you reach, pull, throw, walk or suddenly change direction without you consciously organising every muscle first?
Your nervous system anticipates.
In movement science this is often described as feedforward control or an anticipatory postural adjustment.
Imagine you are standing still and reach quickly to open a heavy door.
Consciously, you probably think the movement begins with your arm.
But your nervous system already knows that moving your arm will change the forces acting through the rest of you.
Research has shown that muscles including the diaphragm and transversus abdominis can begin responding in anticipation of some limb movements, rather than simply waiting for the movement to happen and then reacting afterwards.
Which is pretty amazing when you think about it.
Your breathing diaphragm isn't only involved in breathing.
Your abdominal wall isn't only there for sit-ups.
Your body is continually predicting, organising and adapting.
And that response is not identical for every movement.
Different muscles.
Different timings.
Different directions.
Different loads.
Different jobs.
This is why I am cautious about teaching the body that every movement requires exactly the same deliberate brace.
Bracing itself isn't bad.
Sometimes bracing is precisely what the task requires.
If you are about to lift something very heavy, your strategy is going to look rather different from the one you use to pick up a cup of coffee.
The really clever bit is having options.
Through the work I do, I am much more interested in helping people develop breathing, mobility, strength, body awareness and enough variability that their body has a range of strategies available to it.
Not one answer for everything.
Which brings us back to “switch your core on”
What does that instruction actually mean?
I am always asking the questions… 😂
Which muscle?
How strongly?
For how long?
For what task?
And what happens to your breathing while you are doing it?
Because your body does not require the same abdominal strategy to:
pick up your coffee,
deadlift 80kg,
walk the dog,
cough,
or lie in bed breathing quietly.
The nervous system can scale muscular activity according to demand.
At least, that is what we want it to be able to do.
So I am much less interested in whether somebody can hold their abdomen rigidly for 30 seconds than I am in whether their abdominal wall can change its behaviour appropriately when the task changes.
That is a very different idea of core function.
Strength still matters
This isn't an argument against strength.
Far from it.
The abdominal wall needs to be able to generate force.
It contributes to movement of the trunk, helps transfer load through the body and plays an important role when we increase intra-abdominal pressure.
But strength without options can become just another kind of limitation.
Imagine only having one volume setting on your television.
LOUD.
Fine when you're watching an action film.
Less useful when everyone else has gone to bed.
Our muscular system also needs volume control.
Sometimes the abdominal wall needs considerable force.
Other times it requires very little.
Sometimes one area may shorten while another lengthens.
Sometimes it needs to rapidly generate pressure.
Sometimes it needs to allow movement.
The skill is not simply contraction.
The skill is modulation.
Think about a cough
A cough is a fantastic demonstration of this system.
There is a breath in.
Pressure builds.
The airway temporarily closes.
The diaphragm and abdominal muscles participate in generating pressure.
Then the glottis opens and air is expelled rapidly.
The abdominal muscles are not misbehaving because they created pressure.
Creating pressure was exactly what the task required.
The same principle applies elsewhere in the body.
Pressure is not automatically the enemy.
As we explored in Part 6:
Pressure follows the task.
The question is whether your body has enough options to organise that pressure appropriately.
Now add the pelvic floor
And this is why I struggle with talking about the abdominal wall without talking about the rest of the system.
Below it sits the pelvic floor.
Above it sits the diaphragm.
Around it are the ribs, spine and pelvis.
And the abdominal wall forms part of the boundary between them.
I sometimes describe the abdominal wall as a mirror for the spine.
Not because they copy one another exactly, but because movement of the spine requires changes through the tissues around it.
Flex your spine and the abdominal wall changes shape.
Extend.
Rotate.
Side bend.
The relationships change again.
The abdominal wall cannot be separated from the movement happening behind it.
And changes in one part of this system alter the mechanical environment of the others.
That does not mean the diaphragm, abdominal wall and pelvic floor all move identically every time we breathe.
Human movement is much more variable than that.
But it does mean that treating the pelvic floor as though it exists independently of the abdomen makes very little sense.
Likewise, endlessly training the abdomen without considering breathing, rib movement, pressure, spine, pelvis and pelvic floor gives us only a teeny part of the picture.
They are family.
And family members affect one another.
Try this
Place one hand on your lower ribs and one hand somewhere on your abdominal wall.
Don't change anything initially.
Just breathe.
Notice what moves.
Then make your breath slightly bigger.
What changes?
Now gently blow air out through pursed lips as though cooling a spoonful of soup.
Can you feel the abdominal wall beginning to respond?
Now cough.
Very different strategy.
Now stand up.
Reach one arm overhead.
Turn.
Side bend.
Walk.
Notice how the abdominal wall continually changes shape as the rest of you moves.
That is the bit I want you to notice.
Not whether it feels “on”.
Whether it can change.
The body isn't trying to hold you still
For years, fitness and rehabilitation language has sometimes given us the impression that stability means preventing movement.
Lock the pelvis.
Brace the core.
Keep everything neutral.
Don't let anything move.
But human stability isn't the absence of movement. It is the ability to manage movement. And sometimes that movement is tiny.
Even when you think you are standing completely “still”, your body isn't frozen.
There are constant small adjustments happening.
Your ribcage moves.
Your spine moves.
Your pelvis moves.
Your abdominal wall changes shape.
And your diaphragm moves thousands upon thousands of times each day simply because you breathe. A capable body isn't one that has learned to freeze all of this.
It is one that can organise it.
So perhaps we need a different image
Rather than imagining your abdominal wall as a corset that must constantly be tightened…
Imagine something more alive.
Like that jellyfish bell.
A responsive boundary.
Sometimes firm.
Sometimes yielding and giving way.
Sometimes producing movement.
Sometimes resisting it.
Changing shape.
Transferring force.
Responding to the diaphragm above, the pelvic floor below, the spine behind and the rest of your body around it.
It isn't a simple switch that should permanently be turned ON.
It is much more like a dimmer switch.
And actually, probably hundreds of dimmer switches, continually adjusting to what you are doing.
Because a clever abdominal wall doesn't have one setting.
It has options.
And next, we are going to follow one of the most fascinating parts of this whole conversation, I mean I say that about all of this!!
How does the diaphragm know when to move in the first place?
Because for that, we need to meet the nerve that keeps this extraordinary muscle breathing.
The phrenic nerve.
