In short
Posture matters far less for how it looks than for what runs through it.
Inside your spine is a cord anchored at both ends. When you bend forward it cannot move out of the way. It has to take up the difference itself. Held for hours a day, that becomes a load your body has to manage.
So a slouch is not a cosmetic failing. It is a mechanical demand on the one tissue carrying every signal between your body and your brain.
What follows is where that idea came from, what the measurements show, and what they do not.
What did Alf Breig actually discover?
Breig worked where almost nobody else could: inside the open spinal canal, in the anatomy lab and during neurosurgery, watching the cord as the body was moved. What he described was a continuous tract: the cord and its membranes, the meninges, behaving as one elastic sleeve. Crucially, that sleeve is tethered. It attaches at the base of the skull, again around the upper neck, and at the bottom by a fine strand of tissue running down to the sacrum. Anchored top and bottom, it cannot borrow slack from elsewhere: bend, and the tissue itself must take up the difference. Breig named the sustained version of that load “adverse mechanical tension,” argued it could interfere with how neural tissue works, and argued equally that relieving it could restore function. That claim seeded the modern field of clinical neurodynamics.
Does the spinal cord really stretch when you bend?
It does, and by more than most people expect. In 1981 the French anatomist René Louis published measurements in Anatomia Clinica of how the bony canal itself changes shape with movement. Going from full backward bending to full forward bending, Louis found the canal, the tube, lengthens by roughly five to nine centimetres, with the neck and the low back contributing most of it. Everything inside has to accommodate that. The cord manages it in three stages. First it unfolds: at rest the tissue sits slightly rumpled, like a hose with a gentle wave in it, and that wave straightens out for free. Then it glides, sliding lengthways relative to the canal and drawing towards whichever segment is bending. Only when both of those are used up does the tissue itself elongate. Louis described the plumbing, not disease: the measurements show what moves, not that any posture makes anyone unwell.
Why does stretch matter to a nerve at all?
Because nerve tissue is expensive to run and is fed by very small vessels. Nerves carry their own blood supply, and those vessels do not run straight: they spiral along the nerve, coiled precisely so that they can be stretched without tearing. Past a certain point the coil runs out, the vessels flatten, and flow slows: a garden hose with a foot on it. That is the mechanism, and it is a flow problem long before it is a damage problem.
Wall and colleagues put numbers on it in the Journal of Bone and Joint Surgery in 1992. They applied a measured stretch to rabbit nerve and recorded the electrical signal travelling along it. At six per cent elongation, held for an hour, the size of that signal fell by around seventy per cent; at twelve per cent, conduction stopped altogether. Released within the hour, it largely recovered. Be honest about what that is: an animal study, on a surgically exposed nerve, at strains far beyond anything sitting badly produces. What it establishes is the direction and the currency, nerve tissue is sensitive to sustained tension, and the thing that suffers first is circulation, not the nerve fibre itself.
There is a second reason stillness costs something. As David Butler sets out in The Sensitive Nervous System (2000), the inside of a nerve has no lymphatic drainage of its own; fluid leaves along pressure gradients, helped by the nerve being moved. The cord itself sits in cerebrospinal fluid stirred by breathing and motion. Movement is not merely relief from a position. It is how the tissue does its housekeeping.
Why does my neck ache after a long drive?
Hours up the highway and you get out at the servo already stiff, and walking a lap of the car is the best part of the day. Four separate things are happening. A car seat reclines your pelvis, which flattens the curve in your low back; to keep your eyes level with the road, your head slides forward to compensate, taking the whole tract towards the long end of its range. Your hands are out on the wheel, shoulders held forward, adding length to the nerve pathways running down each arm. The car vibrates, gently, continuously. And you barely move: over a long stretch of road you may not take your neck through one full range even once, so nothing unfolds, nothing glides, nothing gets flushed through.
Two free fixes for any car. Put something firm behind your belt line, a rolled towel, a jumper, so your pelvis sits upright and your head can rest back rather than hang forward. Then set your rear-view mirror one notch higher than feels natural. When you sink, you lose the view; the mirror nags you long before your neck does.
Why does reaching to a high shelf feel odd in the arm?
Reaching for the good bowl on the top shelf, you do something quite specific. The shoulder lifts and rolls back, the elbow straightens, the wrist bends back as your fingers hook the edge, and your head tips back and turns away. That is almost exactly the clinical test practitioners use to put a nerve tract from the neck to the hand on full stretch.
Here is why. The nerves supplying your arm leave the neck, ride over the first rib, pass under the collarbone, through the armpit and down to the fingers. Every joint you open along that route adds a little length, and turning your head away adds the last. So a faint pull, a heaviness, or a fizz in the last two fingers as you strain for that bowl is not mysterious. It is a tract arriving at the end of its range with nothing left to give, and usually it means nothing more than that. Two things make it easier: step in close and use a stool, so the shoulder does the work instead of the whole chain, and turn your head towards the reaching arm, which shortens the pathway rather than lengthening it. If the sensation appears much earlier on one side, or lingers after the arm comes down, mention it to your GP or a Chiropractor.
What can I do about it today?
- Change position before it changes you, brief, full, easy movement several times an hour beats one long stretch. The buffer is restored by variety, not by holding a “correct” shape.
- Raise your screens to eye level, so the head is not drawn forward and down for hours.
- Open the front of the body, a few slow backward bends in a doorway counter the day’s forward curl.
- Breathe into the back of your ribs, three slow breaths, widening sideways rather than lifting the chest, move fluid around the cord.
- Reach smarter, step closer, use a stool, turn your head towards the arm you are reaching with.
- Favour ease over rigidity, a forced military posture creates its own tension.
How does Diskin Life approach the tension Breig described?
Breig’s insight sits near the heart of the way Diskin Life works: what matters about posture is the state of the nervous system living inside it. Rather than prescribing a correct shape, care begins by measuring how a system is actually carrying its load: the Life Assessment draws on digital posturography among its seven extraordinary measures, so tension patterns register as measurements rather than guesswork. The instruments take the picture; the person supplies its meaning, what a change would be worth against the life they want to carry it into, and Dr Ari, drawing on more than forty years of experience, interprets picture and meaning together. Gentle Nervous System Adjustments then use light, precise contacts that cue the nervous system to reorganise, letting the body do the work instead of imposing a shape from outside. The Move theme of the 13 Vitality By Design presentations carries the same principle into daily habits. And anyone curious can begin with a free, no-obligation Discovery Session: a conversation with Dr Ari, nothing more.
What is the shape actually telling you?
A body holds itself the way it has needed to. Read that way, posture is not a fault waiting to be corrected but a piece of plain honesty, feedback, not failure, about the load a nervous system has been carrying and the ways it has found to cope. Which is also why ease cannot be imposed on a spine. It can only be invited, gently, and taken up in the body’s own time. Gentle in the hands, nurturing in the heart, attentive in the mind: that is the manner Diskin Life brings to this work, and to the tissue that carries every signal you have.
An honest limitation
Breig’s anatomy is solid; his clinical claims were bolder than his evidence. The 1978 book is argument and dissection, not controlled trials, and some of his surgical conclusions have not held up. The best modern summary of the therapeutic side, the Basson meta-analysis of neural mobilisation in 2017, found benefits for several nerve-related conditions, though the effects were modest and study quality varied widely. More importantly, population research has never shown a particular posture reliably causes a particular problem: plenty of people with visibly forward heads have no pain, and plenty of upright people do. The mechanics are real, measurable and worth understanding. The leap from mechanics to symptoms is where the evidence genuinely thins, and anyone who tells you otherwise is selling something.
Worth remembering
- Louis (1981) measured the spinal canal lengthening by roughly five to nine centimetres between full backward and full forward bending; the cord accommodates it by unfolding, gliding, then stretching.
- Tension reaches nerves through blood flow first, their tiny spiral vessels flatten under stretch, so duration and stillness matter more than any single position.
- The long drive and the high shelf both take a nerve tract near its end range, and both have free, immediate fixes.
- The anatomy is well established; the link between a given posture and a given symptom is not, so weigh confident claims in either direction carefully.
General information only, not a diagnosis or personal health advice. For persistent pain, numbness, weakness, or any neurological symptoms, please see your GP or a relevant specialist promptly.