FLAT FEET, FALLEN ARCHES AND PRONATED FEET

Much of what is said about flat feet and fallen arches is confusing and wrong.

The term ‘flat feet’ has been used for hundreds of years and was first commented upon by the Greek physician, Galen (c.130-210 AD). However, the foot does not really have an arch that can ‘fall’. Instead, feet have an elastic vault profile that should squash down and then recoil back in a spring-like manner. This is quite unlike an arch built for static stability, as shown in Fig. 1.

Figure 1. Looking side on, feet look like they have an arch with a distinct span distance and a radius of curvature. However, they are built more like an asymmetrical vault that can be squashed down and recoil in a like-spring manner.

A rough guide to effective foot function

During walking, the heel usually makes ground contact before the forefoot and toes. This creates two separate impacts. By doing this, the collision between the foot and the ground is broken into two events that create smaller forces than would one big impact. This distinct two-part ground contact is more pronounced because of the ‘hollow ‘area under the foot that separates the heel from the forefoot. This hollow is what is termed the ‘arch’. However, it is more of an asymmetrical vault shape that involves a range of interlinked continuous curves (see Fig. 2).

Figure 2. Although the foot is commonly said to have an arch, it has many variable but continuous arched profiles The highest profile is noticed most on the inside of the foot (A), but others lie along the outside (B), horizontally running behind the toe joints (C) and transversely across the foot (D). The hashed lines in image C mark the location of the anatomy shown in the curve of D. It is important to stress the continuum of all the cures with each other.

For more about the vault of the foot, click here.

As the heel touches down, muscles pull and compress the foot into a higher profile before the forefoot contacts the ground. Once the entire foot makes ground contact, its vault profile starts to change shape lowering relatively rapidly as muscles relax. This flattening of the foot provides shock absorption, as the shape change is resisted by elastic soft tissues that hold the foot bones together. This makes the foot act like a shock-absorbing spring.

The overall effect of lowering the profile is to create a flatter foot from front to back as it lengthens and widens. This action increases the sole’s surface area in ground contact. Flattening and expanding surface area lowers the peak pressures generated on the sole of the foot. Pressure is force over area. Increasing the foot’s surface in contact with the ground spreads out forces so that peak pressures on tissues are kept to a safer range. Thus, dynamic spring-loaded foot-flattening helps avoid damaging the skin and the deep tissues within the foot.

The foot is easier to ‘squash down’ at the start of bodyweight loading. However, flattening the foot becomes harder the greater and longer it is compressed. This is due to foot flattening creating increasing tensions across the ligaments and tendons that hold the foot bones together. Foot flattening continues as the ankle rotates forward but the foot should become increasingly stiffer as muscle activity increases during this action. Both the flattening of the foot and increasing muscle activity cause the mild curvature running from left to right across the forefoot, to increase. This stiffens the foot and limits how flat the foot can become before the heel lifts.

At heel lift, the foot acts as a semi-stiffened lever to propel forward upon, rotating at the toes. Lifting the heel is something that should only happen after the body’s weight has moved over the forefoot and is moving towards the toes, ready to transfer weight onto the next footstep. Body weight moves off the rearfoot, allowing the Achilles tendon to spring upwards and forward. At the moment of the heel lift, the foot is at its flattest, but it has also become much stiffer and elastic. This results from a combination of increased ligament tensions, greater muscle activity, and by becoming more curved width-wise. At this moment, the other foot is still swinging forward and it should not contact the ground until heel lift occurs on the trailing foot, as shown in Fig. 3.

Figure 3. The weight-bearing foot is usually flattest and stiffest just as the heel lifts, an act that makes the swing foot drop to the ground, as shown in the first two images. As weight transfers onto the next step, the profile of the trailing foot springs back up. However, stiffness now decreases as it does so.

Once the other foot rapidly starts loading, forces on the trailing foot decrease rapidly and the vault profile starts to reform. As body weight forces unload at the end of a step, the foot can spring back into shape. This action sets up cycles of profile flattening and rising, as shown in Fig. 4.

Figure 4. The foot deforms when loaded by body weight, stretching out the soft tissues that hold the foot. As bodyweight offloads, the foot can start to spring back towards its relaxed unloaded shape with the assistance of important muscles located within the calf and under the foot.

The power to lift the heel off the ground towards the end of a step arises from the Achilles tendon. The Achilles is stretched as the ankle rotates forward with the body passing above and over the flattening foot. The stretched Achilles tendon is so full of elastic power towards the end of a footstep as a result, that it wants to pull the heel away from the ground. This becomes easier as body weight moves away from the heel and forward towards the forefoot and toes.

To achieve an efficient heel lift, the foot needs to be semi-stiffened. A stiffer foot means the forefoot can easily push against the ground as the heel lifts, without buckling the foot in the middle. The foot can now pivot around the big (1st), 2nd, and 3rd toe joints as shown in Fig 5.

Figure 5. After the leg has functionally lengthened through hip and knee extension by the middle of single-limb support the foot becomes increasingly stiffer. Ankle rotation is slowed by calf muscle power as body weight (black spot) falls forward. This action stretches and tensions the Achilles elastically. Once body weight has moved over the forefoot, the heel ‘pops up’ off the ground under the recoil power of the Achilles, rotating the foot at the toe joints.

Calf and foot muscles control the rate and extent of foot flattening and stiffening during each step. This activity is aided by changing the curves across the foot vault, which affects how easy it is to stiffen the foot.

Adaptability in stiffness is necessary because different surfaces under the foot require different degrees of foot flexibility. A permanently solid or floppy high-arched or low-arched foot could not provide the required variability. Controlling stiffness across the vault appropriately, avoids ligament, tendon, and joint damage that could result if the foot squashes down too much or insufficiently.

The foot is essentially a squashable spring that can be stiffened or made more flexible by changing its shape and muscle power. That’s basically how a foot works!

The issue

The foot flattens its vault to make it more flexible for shock absorption and to reduce peak pressures under the foot. However, the foot must be stiffer at the point the heel leaves the ground, just when the foot is at its flattest. Therefore, the foot needs to flatten but not by too much.

The solution arises from the action of flattening the foot which also widens and lengthens it. This stretches ligaments and tendons under the forefoot which raises the tensions that stiffen it. By flattening lengthwise, curvatures between the long metatarsal bones across the forefoot increase. So, despite the flattening of the foot lengthwise, width-wise the foot becomes more curved and stiffer. This process is largely achieved by activating muscles under the foot at this time. The foot is therefore supplied with increased stiffness by becoming more curved within the forefoot and compressed together across its joints.

However, if the foot is unable to increase curvature width-wise, it is harder to provide sufficient stiffness to prevent the foot buckling in the middle as the heel lifts, as illustrated in Fig. 6.

Figure 6. Normally, most rotational motion (star in the circle) occurs between the leg and the foot at the ankle while the foot is flat on the ground (A). At this time the Achilles stretches (yellow arrows). However, joints in the middle of the foot also rotate and glide (circle) to flatten the foot as the ankle rotates forward. At heel lift (B), the Achilles elastically shortens and most rotation occurs at the toe joints, significant amounts at the ankle joint, and some within the middle of the foot. Midfoot motion now raises the foot’s profile. If the muscles and soft tissues under the foot are weak or damaged, excessive motion within the middle of the foot will flatten it (C). In these situations, during the start of heel lift, the rearfoot rotates forward and upwards mostly at the midfoot, further flattening the foot profile (D).

Feet that flatten too quickly or excessively, that fail to stiffen sufficiently before heel lift or that remain too stiff throughout a step are those considered to be a problem.

Issues with flat feet, fallen arches, pronation and all that….

So, what are flat feet, fallen arches, dropped metatarsals, and pronated feet?

Human foot shapes exist on a continuum with some rather high-vaulted and others, rather low-vaulted. Most are somewhere in the middle.

None have a perfect profile that makes the foot work best on every single step.

Each differently profiled foot tends to work slightly differently.

Lower vaulted feet tend to be more flexible and higher ones, stiffer. However, the difference in behaviour also depends on the health of the ligaments and the power of the muscles supplying them.

Foot vaults constantly change shape as we walk.

There are times when we need a more flexible foot and other moments when we require a stiffer foot. The processes of stiffening or allowing flexibility are used to manage forces across the foot. Interestingly, habitual barefoot populations tend to have feet that are more adaptable than shod populations. Compared to habitually shod populations, barefoot people appear to demonstrate a higher-than-average static foot profile but utilise flatter-looking feet during walking. However, their feet appear higher arched during running than habitually shod peoples’ feet. This clearly indicates that feet cannot be assessed purely by how they look! It is all about how they function.

Old ideas of classifying feet by their arch profile alone are not appropriate.

Terms like ‘flat feet’, ‘fallen arches’, ‘dropped metatarsals’, and ‘pronated feet’ are still commonly used to explain the development of aches and pains within the feet.

However, these terms make little sense because feet should variably and controllably, lower during every step. Each foot should also appear flatter before the heel lifts from the ground. Metatarsals can be positioned badly, or the soft tissues under them can move out of place, but the metatarsals themselves do not ‘drop’.

Finally, all feet are pronated. Having ‘pronated feet’ might seem like a technical medical term for a serious foot problem, but it is not.

Pronation means to take up a prone position.

When used in reference to the foot, it means that the whole sole faces the ground. So, when standing, the human foot is naturally pronated. During walking and running, the periods when the sole is in full ground contact are the times when the foot is pronated. Pronation is at a peak when the foot is flattest, which should be just before the heel lifts from the ground. Because a foot undergoing motions of pronation is flattening, pronation is a term often used erroneously as a pseudonym for flat feet.

Pronated foot posture is essential to the way humans walk to provide stability. When the foot flattens it increases the sole’s surface contact area, giving us a bigger base of support. When the vault is higher, the foot is less pronated because the foot surface is less prone to the ground. These less pronated foot positions are often called supinated, meaning supine. However, only feet held upside down are truly supine. However, during a step,then the foot is less pronated at heel strike and forefoot contact. It then becomes increasingly pronated until the heel lifts, when it rapidly starts to decrease its pronated posture.

Sometimes feet flatten excessively and start to roll inward unstably. This makes the foot become excessively prone which causes the foot difficulties in creating a stiffer foot to accelerate forward from. If this occurs on every or most steps, this excessive pronation is known as over- or hyper-pronation.

Are flatter feet the source of pain?

Flatter than average feet can be associated with problems, but most foot problems do not relate directly to flat feet.

It is true that some people allow their foot vault to lower excessively or at an inappropriate time. This can be a result of injury or weakness within the feet. However, many flat-looking feet work perfectly well.

Weak muscles that support the foot’s vault often permit too much pronation/flattening, leading to inappropriate foot motion and excessive flexibility at certain joints. This can lead to highly stressed areas within the foot that can become injured.

Feet that pronate/flatten excessively are often referred to as flat feet, pes planus, or pes valgo planus. However, lower profiled feet that work perfectly well are also often called flat feet or pes planus! Feet that have become flatter are usually expressing problems, but feet that have always been flat can function well. Therefore, having ‘flat feet’ might be associated with problems or not.

High-arched feet that do not squash down sufficiently to act as shock absorbers, can also be a problem. They also demonstrate higher pressures on their more limited weight-bearing surfaces on the heel and forefoot. These high-profiled feet are often called pes cavus or cavoid feet and they are usually stiffer feet. Most cavus feet are developmental variations that are often found in shod populations. However, some cavus feet develop due to neurological abnormalities. Feet that start increasing their profile should always be investigated because these feet are likely to be caused by neurological disease.

Generally, feet that flatten too early, too rapidly, excessively or insufficiently are the more likely to be linked to pains and injuries. For a quick summary, see Fig. 7.

Figure 7. Feet are classed into 3 types but in reality, they are all part pf a continuous variation across populations. Most feet have a profile sitting somewhat between the extremes of higher and lower profiles, making it easier to provide changes in stiffness and flexibility. High-arched feet are often stiffer and make poor shock absorbers. Flatter feet are generally more mobile, and if muscles are weak or ligaments lax, they can be too unstable for comfortable walking.

However, feet that appear otherwise normal in shape and motion are not immune from problems. Other causes of foot pain relate to either increases in exercise levels too quickly, poor footwear selection or just the unfortunate consequences of injury, age, and diseases.

How to assist painful flat/pronated feet and falling arches

Rather than considering feet to be too flat, it is more important to consider if they are functioning correctly. Healthy feet easily control the changes in their shape during every step.

It is in consideration of the ability to function that an insole should be selected.

If you just wish to give your feet help and assistance in the long term, consider using Healthy Step insoles in those shoes you are most active in. The Arch angel particularly, is a great extra help for getting the best out of your foot vault’s clever mechanical properties when muscles are at risk of becoming tired.

If you have recently developed some discomfort and aching in your feet, the X-Line Standard or the Arch Angel are the perfect options (see Fig. 9). These are the perfect choices if you have not worn supportive insoles before.

Figure 9. Make sure you pick the right insole for the correct task. The X-Line standard (right) and Arch Angel (left) are the ideal insole for ‘first-time’ mildly painful, achy or tired feet.

If you have had achy, tired, or pain in your feet before and now they are staring again or if you have had foot pains for over 12 months, the X-Line RIF is likely to be the best choice of insole. Many foot and ankle discomforts derive from simple issues that cause muscle fatigue and excessive soft tissue strains. They result in the loss of good control of the foot to change its mechanical properties as we walk. Healthy Step offers a great range of insoles that provide foot function assistance (see Fig. 10).

Figure 10. The X-Line RIF (left) is a long lasting firmer supporting insole. The X-Line ¾ length (middle) enables the use of a vault-supporting insole in footwear with less toe space. while the X-Line. Pressure perfect (right) is soft and cushioning for high-impact activities or more sensitive feet.

Feet that remain too stiff will need some extra help with their ability to shock absorb. Stiffer feet also include the feet of diabetics and those with arthritic feet. High-ached feet also benefit from the addition of extra cushioning. Healthy Step offers the X-Line Pressure Perfect insole for these foot types.

Specific injuries, such as Achilles tendinitis (tendonitis), plantar fasciitis, big toe osteoarthritis (degenerative joint disease), and tibialis posterior dysfunction, require specific features within an insole to assist them improve. This is why Healthy Step has a range of X-Line Condition Specific Insoles. Achilles tendinopathy and calf injuries require the AT insole, plantar fasciitis the PF insole, big toe joint degeneration the DJD insole, and tibialis posterior injuries, the TPD insole (see Fig. 11).

Figure 11. Healthy Step’s clinical experts have designed a range of insoles that assist specific injuries around the foot and ankle. From left to right, the AT is for calf and Achilles problems, the PF for plantar fasciitis (plantar heel pain), the DJD for big toe joint arthritis and pain, and the TPD for problems with the tibialis posterior muscle/tendon and very weak feet.

Not all problems relate to a clear injury. Walking on hard flat surfaces in shoes restricts natural foot motion. This problem, known as an environmental mismatch, seems to be the source of a lot of minor foot ailments through the weakening of the muscles and the sensory nerve supply that provides the controls over foot motion. Many feet require assistance because of the weaknesses developed from footwear use. Using TOETOE® socks offers a simple way to improve your toe function, and can be used in combination with insoles (See Fig. 12).

Figure 12. TOETOE® socks are a great way to spread your toes, just as nature intended.

When using insoles and also for general foot health, Healthy Step recommends using foot and ankle strengthening and mobility exercises frequently. Click here

Exercises greatly improve the situation for your feet in the long term.

The best shoes

We advise the use of lace-up shoes with removable insoles/in-socks for fitting our Healthy Step range of insoles.

However, we appreciate that it might not be possible to fit Healthy step insoles in all shoes. Rather than make your shoe too tight around your toes, consider the X-Line ¾ length when your shoe space is more limited (see Fig. 10).

We also offer support for sling-back sandals with our unique Sandal Saviour and can also help reduce forefoot pains and burning feet, developed from wearing high heels by using Heavenly Heels for dancing or for those formal occasions where nothing else will do (see Fig. 13).

Figure 13. Healthy Step’s clinical designers appreciate that comfortable lace-up shoes cannot be worn all the time. Heavenly Heels (left) and Sandal Saviours (right) give added comfort in the most difficult of footwear.

Sources of Information

The information provided here was sourced from the two medical textbooks written by Healthy Step’s Research and Development Consultant and Product Designer. Both books are extensively referenced from peer-reviewed medical and scientific literature and are published by Academic Press, an imprint of Elsevier.

Clinical Biomechanics in Human Locomotion: Origins and Principles.

Andrew Horwood, with contributions from Nachiappan Chockalingam

ISBN 978-0-323-85212-8

Clinical Biomechanics in Human Locomotion: Gait and Pathomechanical Principles.