Specialist article: body and posture
Shoe insoles and leg length discrepancyWhy the insole does not change the control
One leg is said to be shorter, and now there are insoles in your shoes? Here you will learn why legs of unequal length are the norm, what insoles do and do not achieve, what studies show and why, in our view, the body’s statics begin at the head, with breathing, swallowing and head balance.
Does this sound familiar?
One leg too short, and now there is something in your shoe?
What applies to you?
Tap whatever applies to you.
If several points apply, it is worth looking beyond the feet. In our view, the body usually aligns itself according to head balance, which is coupled with breathing and swallowing. This pattern can be trained.
What studies on leg length showWhy the head sets the paceThe key points at a glance
- Almost nobody has two legs of exactly the same length. In studies, people with and without back pain had differences of the same size on average.
- Insoles support, cushion and distribute load. They do not change the movement pattern that the body has learned over years. For back pain, the body of studies shows no preventive benefit. Our goal is for the foot to do its work itself again and for the insole to become unnecessary step by step.
- In our view, the body’s statics usually begin at the top, with head balance, which is coupled with breathing and swallowing. That is why we train these three functions together instead of only compensating at the bottom.
Video
Shoe insoles and leg length discrepancy: what do orthopaedic insoles achieve?
Das Video lädt erst nach dem Klick. Dann werden Daten an YouTube (Google) übertragen.
No body is a mirror image: unequal legs are the rule
When buying a jacket, you sometimes notice it in the sleeves. One arm is slightly longer than the other. That is not the jacket’s fault.
The two halves of our body do not grow as mirror images. Ears, eyes, hands and feet differ, and so do the arms. The legs are the longest bone chains in the body. It would be astonishing if, of all things, they were identical in length to the millimetre. The measurements show the opposite: almost everyone has a small leg length discrepancy.
of people had legs of unequal length in X-ray measurements, compiled in a review from the USA1
was the average difference, i.e. about half a centimetre1
from around this size, the review considers a difference clinically significant for most people1
A leg length discrepancy of a few millimetres is therefore a normal variant of body build, not a defect. It is different when one leg is clearly shorter after an accident, a growth disorder or a joint replacement. Then the gait pattern may be disturbed, and a compensation in the shoe has its place. This article is not about these cases.
Try it yourself
When standing, you are constantly compensating
Leg length is often measured lying down or standing straight. In everyday life, however, you rarely stand like that.
Stand up and shift your weight from your left leg to your right without taking a step. The loaded leg straightens, the other gives slightly at the knee, and the pelvis tilts along with it. Even this small movement changes the effective leg length by more than a typical insole compensates. When walking, a single leg carries the load for much of the time anyway.
How are you standing right now, while you read this?
Only someone standing rigidly to attention for hours, like a guard of honour, would need two legs of exactly the same length. Everyone else moves with a body that continuously compensates for differences between left and right. That is not a weakness but an achievement of the nervous system.
Research
Leg length discrepancy and back pain: what studies show
That a shorter leg tilts the pelvis and thus causes back pain sounds plausible. It has been tested several times.
In Finland, leg length was measured on X-rays in 247 adults aged between 35 and 54. People who had never had back pain were compared with people who had suffered severely disabling low back pain in the previous year.
was the average leg length discrepancy among the 53 people who had never had back pain, with values up to 20 mm3
was the average among the 78 people with severely disabling low back pain, with values up to 17 mm3
So the groups did not differ. The authors therefore consider an association between mild leg length discrepancy and low back pain questionable3. A case-control study from England, published in The Lancet, likewise found no association between unequal leg length and chronic low back pain4.
People without pain have the same differences as people with pain.A measurement that turns out the same in healthy people as in those affected cannot explain the symptoms.
Finding and cause
When a leg only appears shorter
Often the difference is not measured on an X-ray but compared lying down or read from the position of the pelvis. It is then often unclear what has actually been measured.
The review already cited distinguishes precisely these two forms. The functional discrepancy is described as a phenomenon in its own right, possibly due to increased tension in the muscles above the pelvis. The author recommends resolving it before an anatomical discrepancy is treated2. In other words: first clarify the tension, then consider a compensation.
Head balance deviates
Over a long period, the head sits in front of the body or tilted to one side, often together with mouth breathing and a low-lying tongue.
The body compensates
To keep the centre of gravity over the feet, trunk and pelvic muscles tense more strongly on one side. The nervous system stores this solution.
The pelvis tilts
The uneven tension pulls one side of the pelvis higher. One leg appears shorter, even though the bones hardly differ.
The finding develops
A leg length discrepancy is measured, and a compensation in the shoe is prescribed. The tension that tilts the pelvis remains as it is.
In our view, a measured leg length discrepancy is therefore usually more a reflection of the body’s statics than their cause, measured at the lower end of the system. This does not apply to genuine bony differences, but it does to many of the small differences that are compensated with insoles.
Passive support
What an insole does: support, cushion, distribute load
Apart from length compensation, insoles are mainly common for fallen arches, flat feet with inward-tilting heels, splay foot or flat foot. They are meant to support the arch of the foot so that the foot does not adopt the deviating position in the first place.
Almost every foot deviates from the textbook shape, just as hands and ears differ. A deviation is initially a finding and not yet a disease. It becomes in need of treatment through complaints or structural damage, not through the measurement image. In children, the authors of a Viennese study considered more than 90 % of insole prescriptions to be unnecessary7.
The foot is a mobile system of many small bones, joints, muscles and ligaments. It is built to compensate for unevenness with every step, to deform and to straighten up again.
An insole gives it a predetermined shape. It supports the arch, beds the foot and redistributes pressure. That can feel comfortable, with less pressure pain and more support. It does not change the control that moves the foot.
That an insole feels good is no evidence that the problem has been solved. It takes pressure off the foot as long as it is worn, similar to how a painkiller dampens a headache without clarifying where it comes from. If the complaints return as soon as it is removed, it has alleviated the symptom and not changed the cause.
An insole distributes load. Whether this changes the motor pattern is another question.As long as the aid is in effect, the body works under changed conditions. That does not yet mean it performs the function better by itself afterwards.
Like a crutch
A crutch relieves an injured leg, and that is a good thing. The bone itself has to heal. We see the insole in the same way, and this is not meant disparagingly. It takes work off the foot. But the muscles and the control that are actually supposed to do this work are not given a new task as a result. That is why, as a rule, you do not get rid of insoles as long as nothing changes in the control.
The body continues to compensate around the aid. The nervous system learns to walk with the insole; the old pattern is not overwritten but supplemented. Often the compensation finds another route, in the knee, the hip or the back.
Our goal is therefore for the foot to be able to do its work itself again and for the insole to become unnecessary over time. This happens step by step and together with your practice, not on your own. In cases of genuine indications such as a marked skeletal difference, diabetes or severe malpositions, the insole stays.
Evidence
Insoles for back pain: the evidence
Insoles are prescribed not only for the feet but often also in the hope of relieving the back, hip or knee. There is a review by the Cochrane Collaboration on this.
with random allocation were evaluated in the Cochrane review on insoles and back pain5
took part in the three prevention studies. The authors see strong evidence that insoles do not prevent back pain5
specifically examined the treatment of existing back pain. The data do not allow any conclusion about the effect as a therapy5
Insoles to compensate for a leg length discrepancy were excluded from this review. For them, what the measurements further above show applies: a small difference is found equally in people with and without back pain. Newer forms also have a hard time. So-called sensorimotor insoles are meant to provide stimuli via pads and elevations and to activate the muscles from below.
On 12 June 2025, the German Federal Social Court ruled that German statutory health insurance funds may not pay for them. They are considered a new treatment method without a positive recommendation from the Federal Joint Committee. Their medical benefit has not yet been demonstrated6.
Genuine bony difference
One leg is clearly shorter after an accident, growth disorder or joint replacement, from about 2 cm.
Diabetic foot
Pressure points must be avoided. Here, relief through a fitted insole is important.
Existing damage
With a heel spur, pronounced splay foot or painful misalignments, an insole can relieve pressure.
Congenital or neurological causes
With severe misalignments, for example after paralysis, insoles or orthopaedic shoes are often indispensable.
In these cases, an insole has its firm place, as relief. Training the basic functions can be combined with insoles.
Body statics
Head balance as the starting point of the body’s statics
Behind many insoles lies the idea that a faulty foot makes the whole body unstable. In our view, the chain usually runs the other way round.
The body is often compared to a tower that above all needs a solid foundation. In the Taipei 101 skyscraper in Taiwan, the engineers solved stability differently. In the upper part of the tower hangs a movably suspended steel sphere weighing many tonnes.
This sphere, a so-called tuned mass damper, swings against the movements of the building during storms and earthquakes. The tower is thus stabilised from above. For us, the head is this sphere.
The head houses the eyes and the organ of balance. As early as the 1920s, the physiologist Rudolf Magnus in Utrecht described how righting reflexes first align the head, and the neck, trunk and pelvis follow it. Accordingly, the Cranio-Cervical Functional Model, CCFM for short, the working model of Sabine and Klaus Berndsen, states: the position of the head aligns the line of gravity.
If the head drifts forward or tilts to the side, the body below has to compensate, with the neck, shoulders, spine and pelvis, all the way down to the knees and feet. In this picture, a fallen arch or flat foot with an inward-tilting heel can also be a consequence, a sign that the system is compensating from above.
You can find more about forward head posture, text neck and the paths from the neck into the back in the article on neck pain and back pain.
The foot is the end of the chain, not its beginning.In our view, anyone who only compensates at the bottom is treating the finding at the wrong end of the system.
The triad
Breathing and swallowing help carry the head
Why can’t you simply resolve to stand up straight? Because head balance is not an act of will but a basic function that is coupled with two others.
Breathing
If the nose is narrow or the mouth open, the body pushes the head forward to widen the airway. The muscle chain in front of the neck loses its pull.
Swallowing
After every swallow, the tongue settles against the palate. If it rests in the tongue reference position, the front neck muscles stabilise the head. If it lies low, this support is missing.
Head balance
If the head is balanced above the cervical spine, it is carried rather than held. The neck, back, pelvis and feet do not have to readjust.
Try it out. Place the tip of your tongue on the small ridge behind your upper front teeth. Swallow once, leave the tip of your tongue there and then hold the tension. Feel with your fingers on your neck how your throat and the back of your neck change.
This is the muscle chain that stabilises the head from the front. You swallow many hundreds to a thousand times a day. If your tongue rests in its reference position while doing so, each swallow also trains this chain.
The three functions reinforce each other. If the head moves forward, the mouth opens more easily. If the mouth is open, the tongue sinks and the air takes the route through the mouth. If support is lacking when swallowing, the head drifts further forward. You can find more on the tongue under tongue reference position, and on the role of breathing during sleep under snoring and sleep apnoea.
In our view, this triadic functional circuit of breathing, swallowing and head balance stands at the beginning of many causal chains that reach down into the back, pelvis and feet. It extends into the pressure chamber formed by the diaphragm and the pelvic floor. Muscles that are not involved in their function are not used and lose tension. Once involved, they regain it.
Children
Children’s feet: observe and move
Children in particular are often given insoles because their feet look flat. Yet a flat foot in the first years of life is a stage of development.
of three-year-old children had flat feet in a Viennese study of 835 children; among six-year-olds, it was still 24%7
of flat feet were pathological; the rest were flexible and part of normal development7
of children wore insoles. The authors considered more than 90% of the treatments unnecessary7
The arch of the foot forms during childhood through use. Walking barefoot on varying surfaces, climbing, balancing and jumping challenge the small foot muscles. In our view, the same applies to children’s feet as to any other function: what is used develops. What is constantly supported has to do less.
With children, it is also worth looking upwards. If the mouth is often open, the child snores or holds its head tilted forward, precisely the functions from which posture originates are affected. More on this under FaceFormer for children.
If a child’s foot is stiff, painful or markedly altered on one side, it should be examined by a paediatric orthopaedic specialist.
Active rather than passive
Training instead of supporting: from foot to head
If a support does not change the control, something is needed that addresses the control. That is training, at the foot as well as at the basic functions.
The foot is an organ of movement and not a support. If it is constantly in a shoe that dictates its shape, this takes work off it, and the small foot muscles can become weaker as a result8. If an insole is added, in our view it becomes a crutch for the crutch. This explains why many mild foot malpositions do not improve with supports. What challenges the foot, on the other hand, makes it stronger.
For the foot itself, there is a randomised study from the USA. For eight weeks, 57 runners either walked increasingly in minimalist shoes, did targeted foot exercises or changed nothing.
In both active groups, the foot muscles became larger and stronger, but not in the comparison group. Walking in minimalist shoes was as effective as the exercises8. Walking barefoot on grass or sand challenges the foot in a similar way.
Passive support
- Insole, wedge or shoe raise
- Works as long as it is worn
- Changes shape and pressure distribution
- The control pattern stays as it is
Active training
- Foot, breathing, swallowing and head balance
- Addresses the control
- Requires repetition over months
- The goal is a pattern that runs by itself
The two are not mutually exclusive. The training can be started with an insole, which is then needed less and less step by step.
FaceFormer therapy starts at the top. In the basic exercise, the FaceFormer sits in the oral vestibule. Straighten your head, lengthen your neck, tip of the tongue to the palate, breathe through your nose. Then you press the lip wedge, bite down briefly and swallow.
Later, the pull exercise and the head balance rotation are added. This way, you practise breathing, swallowing and head balance in the same sequence.
- From day 1
Basic exercise
Three times a day for a few minutes with the FaceFormer ZERO.
- After a few weeks
Pull exercise and night
The pull exercise is added, and at night you wear the FaceFormer ZERO.
- After a few weeks
Switching to the ONE
During the day the FaceFormer ONE, the same size as the ZERO, just made of firmer material.
- Further on
Head balance rotation
Turning the head connects the training with the neck muscles.
- Over 6 to 12 months
The pattern runs by itself
This is followed by maintenance training.
The free FaceFormer app guides you through the basic exercises; you will find all modules on the exercise pages. There is as yet no randomised study on FaceFormer therapy for leg length discrepancy or foot misalignments. The absence of a study does not mean that the connection does not exist, but that it has not been tested. All our own work is listed under Studies and science.
Everyday life
Challenge your feet, balance your head: ideas for everyday life
Go barefoot more often
Walk barefoot at home, in the garden or on the beach. Uneven ground challenges the small foot muscles with every step.
Switch your standing leg
When standing, it is fine to turn one leg out. Just switch sides more often instead of always loading the same leg.
Shoes with room
Shoes with enough room for the toes and a flexible sole let the foot do its work.
Lips closed, nose open
The lips rest loosely together, the tip of the tongue on the palate behind the upper front teeth. This helps the head into balance.
Look straight ahead
Place your screen and laptop at eye level and raise your phone instead of lowering your head.
Discuss your insoles
If you wear insoles, talk to your practice about what they are intended for and whether, alongside the training, you can gradually wear them less often.
Questions
Frequently asked
Is a leg length discrepancy normal?
Yes. In X-ray measurements, around 90% of people have legs of unequal length, on average by about half a centimetre. For most people, a difference is only considered clinically significant from about 2 cm. Smaller differences are a normal variant of body build.
When should a leg length discrepancy be compensated?
With a genuine bony difference, for example after an accident, a growth disorder or a joint replacement, and from about 2 cm, a compensation in the shoe can improve the gait pattern. With just a few millimetres, in our view the first question is whether the leg only appears shorter because muscle tension and pelvic position have changed.
Can a leg length discrepancy cause back pain?
For small differences, this has not been demonstrated. In a Finnish study, people without back pain had on average the same leg length discrepancy as people with severe low back pain, and an English case-control study also found no association. In our view, the cause usually lies in the body’s statics, which start from head balance.
Do insoles help against back pain?
A Cochrane review of six randomised trials found strong evidence that insoles do not prevent back pain. For the treatment of existing back pain, the data do not allow any conclusion. Insoles can feel comfortable, but they do not change the movement pattern.
What did the Federal Social Court decide on sensorimotor insoles?
On 12 June 2025, the German Federal Social Court (Bundessozialgericht) ruled that German statutory health insurance funds may not pay for sensorimotor insoles. They are considered a new treatment method without a positive recommendation from the Federal Joint Committee (Gemeinsamer Bundesausschuss); their medical benefit has not yet been demonstrated.
Do children with flat feet need insoles?
According to the Vienna study, usually not. In a Vienna study, more than half of three-year-olds had flexible flat feet, and just under a quarter of six-year-olds still did; fewer than 1% were pathological. Movement and walking barefoot challenge the foot. If a child’s foot is stiff or painful, it should be examined.
Should I simply stop wearing my insoles?
Not on your own. But our goal is for the foot to be able to do its work itself again and for the insole to become unnecessary over time. This happens step by step and together with your practice, while you train your feet and basic functions. In cases of genuine indications such as a marked skeletal difference, diabetes or severe malpositions, the insole stays.
More articles from the knowledge section
Where to go next
Sources
- Knutson GA (2005). Anatomic and functional leg-length inequality: a review and recommendation for clinical decision-making. Part I, anatomic leg-length inequality: prevalence, magnitude, effects and clinical significance. Chiropractic & Osteopathy 13:11. PMID 16026625. Source
- Knutson GA (2005). Anatomic and functional leg-length inequality: a review and recommendation for clinical decision-making. Part II. The functional or unloaded leg-length asymmetry. Chiropractic & Osteopathy 13:12. PMID 16080787. Source
- Soukka A, Alaranta H, Tallroth K, Heliövaara M (1991). Leg-length inequality in people of working age. The association between mild inequality and low-back pain is questionable. Spine 16(4):429-431. PMID 1828627. Source
- Grundy PF, Roberts CJ (1984). Does unequal leg length cause back pain? A case-control study. The Lancet 2(8397):256-258. PMID 6146810. Source
- Sahar T, Cohen MJ, Ne’eman V, Kandel L, Odebiyi DO, Lev I, Brezis M, Lahad A (2007). Insoles for prevention and treatment of back pain. Cochrane Database of Systematic Reviews (4):CD005275. PMID 17943845. Source
- Bundessozialgericht (German Federal Social Court), judgment of 12.06.2025, ref. B 3 KR 12/23 R (sensorimotor insoles, provision of medical aids). Source
- Pfeiffer M, Kotz R, Ledl T, Hauser G, Sluga M (2006). Prevalence of flat foot in preschool-aged children. Pediatrics 118(2):634-639. PMID 16882817. Source
- Ridge ST, Olsen MT, Bruening DA, Jurgensmeier K, Griffin D, Davis IS, Johnson AW (2019). Walking in Minimalist Shoes Is Effective for Strengthening Foot Muscles. Medicine & Science in Sports & Exercise 51(1):104-113. PMID 30113521. Source
Get started
Ready for the training?
The free FaceFormer app guides you through the basic exercises, counts along and reminds you of your sessions. If you wish, a practice from the practitioner directory can support you.
FaceFormer ZERO + ONE
Both material hardnesses for getting started, day and night. The set for adults.
FaceFormer ZERO
The softer FaceFormer for getting started, for children and for the night.
FaceFormer ZERO Children’s Set
ZERO with hygiene box, plush bag and success book with stamp.
FaceFormer training aims to restore the physiological setting of the basic functions of breathing, swallowing and head balance, with lip closure and the tongue reference position, thereby creating the conditions under which symptoms can improve. It does not replace a medical assessment. You can find practitioners near you in the practitioner directory.
