Flat Feet and Running: What Actually Helps

Few orthopaedic diagnoses trigger such a reliable chain of consequences as flat feet: insoles, stability shoes, treadmill gait analysis, cutting back on long runs. Very few of those measures are supported by the evidence. A low arch is first of all an anatomical variant — common, mostly symptom-free and present in a large share of the population. It becomes a problem only when it produces pain, and even then the cause lies less often in the arch itself than in what the foot is asked to do every day.

What flat foot is — and what it is not

In flat foot, medically pes planus, the medial longitudinal arch sits flattened against the ground. Two forms are distinguished, and the difference matters in practice. The flexible flat foot is flattened when standing but re-forms on tiptoe or during roll-through — this is the normal case and as a rule causes no trouble. The rigid flat foot stays flat on tiptoe too, often combined with limited mobility in the lower ankle joint; it should be assessed, because a bony deformity or a fusion may sit behind it.

Prevalence is reported at 15 to 25 percent of adults in studies, depending on definition and measurement method. In running cohorts the share is similarly high. That alone gives the most important context: a trait that one in four runners has cannot automatically be a cause of injury. There is no reason to restrict training because of a flexible flat foot.

Pronation is not a design flaw

Pronation — the slight inward roll of the foot after first ground contact — is a cushioning movement, not a malfunction. It spreads the impact forces over time, unloads the ankle joint and can be measured in every runner. Runners with a low arch often pronate more and for longer, but the boundary between "normal" and "excessive" has never been cleanly defined in research. There is no generally accepted threshold in degrees or millimetres.

The biomechanist Benno Nigg pursued this point over decades and formulated the provocative consequence: pronation follows no ideal image, and trying to force it towards a norm via shoe or insole does not lead to fewer injuries. His work shows that the foot's individual preference — what feels comfortable — is a better predictor of staying symptom-free than any deviation from a theoretical ideal line.

Why flat feet alone rarely hurt

The evidence here is surprisingly clear. Reviews that set arch height against injury rates in runners find no robust association between a low arch and the occurrence of overuse injuries. A systematic review across several thousand runners concluded that foot shape is unsuitable as a screening criterion — neither sensitivity nor specificity is sufficient to derive training recommendations from it.

What does correlate robustly with symptoms is unspectacular: too rapid an increase in volume, a sudden change of shoe or surface, missing strength in calf and foot musculature, too little sleep and a chronically too-fast everyday pace. In these cases the flat foot acts as an amplifier, not a cause: a foot whose muscles have to stabilise 40 kilometres a week without ever being trained for it will eventually complain — regardless of how high its arch is.

Shoes: what the data says about stability models

Stability shoes with anti-pronation elements were the standard recommendation for low arches for two decades. The evidence for it is thin. The largest randomised trial on the subject — more than 900 runners, 12 weeks of observation — found no difference in injury rates between stability and neutral shoes. A later study with over 1,500 runners reached the same conclusion, regardless of how pronounced the pronation was.

In practice that means: the shoe has to fit the foot, not the diagnosis. Three criteria have proven useful:

• Fit before category. No pressure on the inside of the midfoot, no pinch in the forefoot, roughly a thumb's width of space in front of the longest toe. A shoe that presses on the medial side worsens the very symptoms it is meant to prevent.
• Not too soft. Very soft cushioning sounds pleasant but costs stability during roll-through when the arch is low. A medium level of cushioning with a firmer heel counter works better for most runners than maximum cushioning.
• No abrupt switch. Moving from an old, worn-out pair to a new shoe with a different drop is one of the most common causes of Achilles and plantar symptoms. Alternating the two for two weeks is usually enough.

More on shoe choice in general is in Buying running shoes and Breaking in running shoes. If you want to know how your foot actually rolls through, the methods are in Gait analysis — with the caveat that a one-off video analysis in a shop says less than what the foot reports after 20 kilometres.

Insoles: when they help and when they don't

Insoles are not nonsense — they are just often the wrong first measure. What the studies show is a clear time course: in the short term, over four to eight weeks, orthopaedic insoles measurably reduce pain in the sole and the shin. In the medium term the advantage disappears. After twelve weeks, the results of a simple foot strength programme are at least equivalent, and in several studies better.

That is logical once you consider what an insole does: it takes over support work the foot could do itself. If it is worn permanently without the musculature working alongside, you end up with exactly the state you wanted to avoid. Insoles therefore make sense in three situations:

• Acute phase. When walking and running are barely possible because of pain in the plantar fascia or the inner ankle, an insole bridges the time until training takes effect.
• Rigid deformity. When the arch is structurally no longer correctable, passive support is permanently justified.
• Underlying disease. With rheumatological conditions, neuropathies or after fractures, different rules apply — that belongs in orthopaedic care.

For a flexible flat foot without comorbidity the order is therefore: strength and load management first, the insole as a tool for the transition period, not as a permanent solution. To separate this from other foot complaints, see Plantar fasciitis and Foot strength for runners.

The training that actually stabilises the foot

The musculature that actively holds the longitudinal arch can be trained: the toe flexors, the tibialis posterior on the inside of the lower leg and the short muscles of the foot. A programme addressing these three groups needs three sessions of 10 to 12 minutes per week. Four exercises are enough:

• Heel raise with emphasis on the big toe. Slowly up, hold for two seconds, slowly down. Three sets of 12 repetitions, barefoot. The point is not the height but the controlled lowering phase — it trains exactly the phase in which the arch gives way.
• Towel scrunching. Pull a towel across the floor with your toes, 30 seconds per foot, three rounds. Sounds like little, but hits the short toe flexors directly.
• Posterior tibialis exercise. Sitting down, place a resistance band around the forefoot and guide the foot inwards against the pull, three sets of 15 repetitions. In a low arch this muscle is often the weakest link.
• Single-leg stand with eyes closed. Three times 30 seconds per side. Not a foot exercise as such, but the ankle control that keeps the foot from rolling over uncontrolled.

Add progressive loading in everyday life: go barefoot wherever possible — grass, home, park. The stimulus is not barefoot romance but the wider range of motion a shoe prevents. Anyone considering barefoot running should know the rules in Barefoot running: start with minimal distance and increase volume over months, not weeks.

None of this is a detour from running economy. A foot that rolls through in a controlled way loses less energy in the cushioning phase — the same logic behind Running economy and Improving running technique. Cadence is a useful indicator here: runners well below 160 steps per minute often have a long ground contact time with strong pronation. Raising it by five percent — no more — shortens contact and reduces peak load. Details in Running cadence.

Manage the load instead of correcting the arch

The most effective lever for foot complaints is undramatic: slow the increase in volume and dose the hard sessions. The rule of no more than ten percent per week is crude, but the direction is right. More informative is the ratio of acute to chronic load — the last seven days compared with the last 28. If it stays above 1.3, injury risk rises clearly. How to calculate it is in ACWR and training load.

With an acute flare-up in the sole or inner ankle, the usual staging applies: unload for two to three days but do not stop completely — cycling, swimming and strength work maintain fitness. Then return with short, slow runs on soft ground, every other day, and only rebuild volume after a symptom-free week. The full step-by-step plan is in Return to running after injury and The pain traffic light.

One point that is often missed: flat foot is also a question of the whole leg chain. A knee collapsing inwards, weak hip abduction and limited ankle mobility all amplify pronation from above. That is why hip and glute work belongs in every programme for runners with foot complaints — not as an add-on but as part of the solution. Background in Gluteal amnesia and Balance training for runners.

When to see a doctor or physiotherapist

Most flat-foot complaints can be solved with training and patience. Five situations, however, belong in professional assessment:

• Rigid flat foot. No arch on tiptoe, limited mobility — bony causes or a tendon disorder of the posterior tibialis may sit behind this.
• One-sided flat foot. A sudden change in just one foot always warrants assessment, because it can indicate nerve damage or a tendon rupture.
• Pain at the inner ankle. Posterior tibial tendon dysfunction is its own condition with its own treatment and must not be dismissed as "just flat feet".
• Symptoms beyond eight weeks. If a structured strength programme has changed nothing after two months, either the diagnosis or the approach is wrong.
• Neurological symptoms. Numbness, tingling, loss of strength — that needs prompt assessment, not training.

The reverse also holds: a flexible flat foot without pain is not a case for treatment. Anyone who gives up intervals or long runs because of it loses training quality for nothing in return.

How Peakora handles it

Peakora is not a medical tool and does not make diagnoses. What the engine does is manage load: when you come back from a foot episode with reduced volume, the system works with CTL, ATL and TSB and rebuilds the week accordingly instead of throwing you back into the old structure. Session types can be adjusted when less running pace is sensible for a while. The terms are explained in the glossary; for the recovery logic behind it, see Recovery in endurance sport.

The honest closing sentence: a low arch is a property, not a disease. What makes a foot stable is strength, a shoe that fits and a load that can increase without the tendons falling behind. That is less spectacular than the right insole — but it lasts longer.

Frequently asked questions