Flat Feet and Running: Why They're Probably Not Your Problem

If you have flat feet and you run, someone has probably told you it is a problem. A shoe-shop assistant, a physio, a friend, a running blog. Motion control shoes, orthotics, arch support — an entire category of products exists on the assumption that a low arch needs fixing before it hurts you.

The research on runners does not support that assumption.

What the injury studies found

In 2022, a systematic review and meta-analysis pooled 30 prospective studies covering 3,404 runners — studies that measured foot posture first and then followed people forward to see who got hurt. Foot posture type was not associated with injury rates.¹

That finding is not new. A 2002 prospective study of 196 athletes found that pes planus did not predict lower-extremity injury; sex and contact-sport participation did.² An earlier 2013 meta-analysis did report a weak association between non-neutral foot types and injury, but mixed cross-sectional studies with prospective ones, and its authors noted the result depended heavily on how "flat foot" was defined.³

Clinically, flexible flat feet without symptoms have long been described as a benign variant with no justification for intervention.⁴ Somewhere between 15% and 30% of adults have them, depending on the study and the definition, and most of those adults are fine.

When flat feet do matter

"Usually not a problem" is not "never a problem." Three situations are different, and all three are a clinician's call rather than a product's:

• Pain. A flat foot that hurts — arch, inner ankle, heel — is symptomatic, and symptomatic pes planus is treated differently from the painless kind.
• Rigid flatfoot. About 1% of people have an arch that does not change between sitting and standing. That is a structural condition with its own causes.
• An arch that has recently dropped. In adults, a newly acquired flat foot — particularly on one side — can signal posterior tibial tendon dysfunction and should be assessed.

If any of those describes you, see a podiatrist or sports physician before you buy anything, including from us.

What foot training actually does to an arch

Here is the part that is real, and it is narrower than the marketing.

Training the small muscles inside the foot measurably changes how the arch behaves. A 2023 meta-analysis of 13 randomized trials found that intrinsic foot muscle training significantly reduced navicular drop — a standard measure of how far the arch collapses under load.⁵ In runners specifically, eight weeks of foot-core training reduced how much the medial longitudinal arch moved through the stance phase of running.⁶ A 2022 meta-analysis that included three studies in people with pes planus found improved dynamic balance.⁷

So: foot training makes a low arch behave more stiffly under load. That is a measured effect. What it is not is a cure for flat feet, a treatment for foot pain, or a proven way to prevent running injuries in flat-footed runners. The trials measured arch mechanics and balance, not those outcomes. The same 13-trial meta-analysis found no significant improvement in pain.

Where Toe-Rx fits

Toe-Rx is a tool for the training above. It holds the toes open wider than you can unassisted and gives them something to close against. In the one trial that isolated it, wearing a spacer alone changed nothing over eight weeks; adding the active movement changed everything measured.⁸ Ten minutes, sitting down, every other day. How to use it is here.

It does not cure flat feet. We said that in the previous version of this article too, and it was the one sentence worth keeping. What we have added is the rest of the picture: that your flat feet are probably not hurting your running, that foot training changes arch mechanics rather than arch shape, and that if your foot hurts, the answer is a clinician.

For what actually reduces running injuries — a year-long randomized trial of foot strengthening in runners, and what it does and doesn't prove — see the runners' page.

Choosing a size

Toe-Rx is not one-size-fits-all: three sizes, two firmnesses. Wearing the wrong size is uncomfortable and can cause injury. Start from your everyday shoe size and the Soft type, and check the sizing guide. If it pinches or slips, we will exchange it.

*These statements have not been evaluated by the FDA. This product is not intended to diagnose, treat, cure, or prevent any disease.

References

1. Systematic review and meta-analysis of foot posture and running-related injury, 30 prospective studies, n = 3,404 runners. 2022.
   CITATION INCOMPLETE — see notes. Load-bearing for this article.
2. Michelson JD, Durant DM, McFarland E. The injury risk associated with pes planus in athletes. Foot & Ankle International. 2002;23(7):629–633. PMID: 12146774. Read it
   Prospective, 196 athletes, 227 lower-extremity injuries.
3. Tong JWK, Kong PW. Association between foot type and lower extremity injuries: systematic literature review with meta-analysis. Journal of Orthopaedic & Sports Physical Therapy. 2013.
   Found a weak association; mixed study designs; result depended on how flat foot was defined. Confirm volume and pages.
4. Staheli LT. Planovalgus foot deformity: current status. Journal of the American Podiatric Medical Association. 1999;89(2):94–99.
   Cited via Banwell et al. 2012 (J Foot Ankle Res). Confirm the original before publishing.
5. Jaffri AH, Koldenhoven R, Saliba S, Hertel J. Evidence for intrinsic foot muscle training in improving foot function: a systematic review and meta-analysis. Journal of Athletic Training. 2023;58(11–12):941–951. doi:10.4085/1062-6050-0162.22. PMID: 35724360. Read it
6. Matias AB, Watari R, Taddei UT, et al. Effects of foot-core training on foot-ankle kinematics and running kinetics in runners: secondary outcomes from a randomized controlled trial. Frontiers in Bioengineering and Biotechnology. 2022. doi:10.3389/fbioe.2022.890428
7. Wei Z, Zeng Z, Liu M, Wang L. Effect of intrinsic foot muscles training on foot function and dynamic postural balance: a systematic review and meta-analysis. PLOS ONE. 2022;17(4):e0266525. doi:10.1371/journal.pone.0266525. Read it
   16 studies; three in pes planus (n = 75).
8. Kim MH, Yi CH, Weon JH, Cynn HS, Jung DY, Kwon OY. Effect of toe-spread-out exercise on hallux valgus angle and cross-sectional area of abductor hallucis muscle in subjects with hallux valgus. Journal of Physical Therapy Science. 2015;27(4):1019–1022. doi:10.1589/jpts.27.1019. Read it