Feet are muscles. And muscles adapt.
This is the long version — for the people who want the proof, not just the promise. The science of how your feet are built, how modern life quietly switched them off, and exactly how they retrain. Every claim below is sourced.
Educational, not medical advice. Citations are listed at the foot of the page.
An engineering masterpiece you walk on every day
Leonardo da Vinci called the human foot “a masterpiece of engineering and a work of art.” He wasn't exaggerating. Each foot packs 26 bones, 33 joints and more than 100 muscles, tendons and ligaments — roughly a quarter of your entire skeleton lives below your ankles.
Those muscles come in two families. The big extrinsic muscles start up in your shin and pull on the foot through long tendons. The small intrinsic muscles live entirely inside the foot — the local stabilisers that fine-tune the arch and control your toes. In 2015 researchers gave them a name: the “foot core.” Just like the core that braces your spine, a strong foot core stabilises every single step — and the big leg muscles simply can't do its job.
Your arch is a spring — and your big toe is the trigger
The arch isn't a static support. It's a spring. As you load each step the arch flattens slightly, stretching the plantar fascia and storing elastic energy; as you push off it recoils and gives that energy back. Cadaver testing puts it at roughly 17% of the energy of every running stride — free propulsion you'd otherwise have to generate from scratch.
What arms the spring is the windlass mechanism: as your big toe extends at the end of each step, the plantar fascia winds tight around the joint like a cable on a drum, stiffening the arch into a rigid lever for push-off. Which is why a big toe that can move freely — and toes with room to spread — matter so much. A wide, splayed base is simply a bigger, steadier platform to stand and push from.
You were, quite literally, born to move
Step into the volcanic ash at Laetoli, Tanzania and you'll find footprints 3.6 million years old — already upright, already with an in-line big toe built for push-off, long before the first shoe existed. In a landmark 2004 Nature paper, “Endurance running and the evolution of Homo,” Bramble and Lieberman argued that the arch, the short toes and the springy tendons are part of a body shaped to cover long distances on foot.
That heritage is still visible. Born to Run introduced millions of readers to the Rarámuri — “the running people” of Mexico's Copper Canyons — who cover extraordinary distances in thin huarache sandals. As Christopher McDougall put it: “If you don't think you were born to run, you're not only denying history — you're denying who you are.”
We were born to run; we were born because we run.Christopher McDougall, Born to Run (2009)
You've been walking in casts your whole life
Put a healthy arm in a cast for a few weeks and the muscle inside withers — not because anything is broken, but because nothing is being asked of it. Modern footwear does something similar, gently, for decades. Narrow toe boxes squeeze the toes out of their natural splay. Raised heels tip your load forward. Thick cushioning and stiff arch support do the foot's stabilising work for it.
The fingerprints show up in the research. Populations that grow up barefoot tend to have wider feet and more evenly spread pressure than habitually shod ones. And those plush soles come at a sensory cost: the bottom of your foot is a dense sensor array feeding your balance system, and cushioning measurably muffles that signal. None of this is damage. It's disuse.
This isn't ageing. It's disuse — and disuse reverses.
The small muscles of the foot obey the same rule as every other muscle: use them and they adapt; ignore them and they fade. The encouraging half is that they're demonstrably trainable — strength, size and balance all improve with consistent loading, in studies of adults well over 65. Weak feet are not a fixed fate.
The evidence that feet actually retrain
This is the part the skeptic wants. Not vibes — trials.
Strength comes back. Western adults who simply switched to minimal footwear for daily activity raised their foot strength by an average of 57% over six months (Curtis & D'Août, 2021). Eight weeks of minimalist walking grew intrinsic foot muscles about as much as a dedicated strengthening programme (Ridge, 2019).
Stronger feet get hurt less. Runners who did an 8-week foot-core programme had roughly 2.4× fewer running injuries over the following year — and baseline foot strength was the single best predictor of staying healthy (Taddei, 2020).
Balance is trainable — and it matters. Failing a simple 10-second one-leg stand was linked to 1.84× higher mortality in over-50s (Araujo, 2022). Balance is a skill, and skills improve with practice.
Four capacities, four bodies of evidence
Release
Self-massage of the sole improves tissue pliability and flexibility, prepping the foot to load and spring.
Splay
Toe-spread drills fire the abductor hallucis and intrinsics — building a wider, more stable base.
Strengthen
Loaded foot muscles measurably grow in size and strength, just like any other muscle.
Balance
Proprioceptive training sharpens single-leg balance and steadier, more confident movement.
References & further reading
- McKeon PO, Hertel J, Bramble D, Davis I. The foot core system: a new paradigm for understanding intrinsic foot muscle function. British Journal of Sports Medicine. 2015;49(5):290.
- Ker RF, Bennett MB, Bibby SR, Kester RC, Alexander RM. The spring in the arch of the human foot. Nature. 1987;325:147–149.
- Curtis R, Willems C, Paoletti P, D'Août K. Daily activity in minimal footwear increases foot strength. Scientific Reports. 2021;11:18648.
- Ridge ST, Olsen MT, Bruening DA, et al. Walking in Minimalist Shoes Is Effective for Strengthening Foot Muscles. Medicine & Science in Sports & Exercise. 2019;51(1):104–113.
- Taddei UT, Matias AB, Duarte M, Sacco ICN. Foot Core Training to Prevent Running-Related Injuries: A Survival Analysis of a Single-Blind, Randomized Controlled Trial. American Journal of Sports Medicine. 2020;48(14):3610–3619.
- Araujo CG, de Souza e Silva CG, Laukkanen JA, et al. Successful 10-second one-legged stance performance predicts survival in middle-aged and older individuals. British Journal of Sports Medicine. 2022;56(17):975–980.
- Bramble DM, Lieberman DE. Endurance running and the evolution of Homo. Nature. 2004;432:345–352.
- Lieberman DE, et al. Foot strike patterns and collision forces in habitually barefoot versus shod runners. Nature. 2010;463:531–535.
- D'Août K, Pataky TC, De Clercq D, Aerts P. The effects of habitual footwear use: foot shape and function in native barefoot walkers. Footwear Science. 2009;1(2):81–94.
- Hollander K, et al. Growing up (habitually) barefoot influences the development of foot and arch morphology. Scientific Reports. 2017;7:8079.
- Viseux FJF. The sensory role of the sole of the foot: review and update on clinical perspectives. Neurophysiologie Clinique. 2020;50(1):55–68.
- Wei Z, et al. Effect of intrinsic foot muscle training on foot function and dynamic postural balance: A systematic review and meta-analysis. PLoS One. 2022;17(4):e0266525.
- McDougall C. Born to Run: A Hidden Tribe, Superathletes, and the Greatest Race the World Has Never Seen. New York: Alfred A. Knopf; 2009.
The Splay Lab is a training system for foot strength, mobility, balance and comfort. It is not a medical device and is not intended to diagnose, treat or cure any condition, including bunions or flat feet. If you have foot pain or a diagnosed condition, consult a qualified clinician before starting.