Do You Actually Need Shoe Insoles? Short Answer: No.

What you actually need is a shield against flat ground. Not something that pads your foot, not something that props it up — something that changes what your foot is standing on.

That's a different category than everything in the pharmacy aisle, and the difference is a simple one: most insoles are a bandage. They manage a foot that's already reacting badly to something — the way a cast manages a bone that's already broken. A shield works upstream of that. It removes what's causing your ligaments, tendons, and joints to overwork in the first place: a foot built for uneven ground, standing on flat, hard ground all day, every day. One manages the symptom. The other removes the cause.

Every pharmacy has that aisle: a dozen boxes of insoles, most claiming some version of "support" or "comfort" without naming a mechanism you could check. There's also a barefoot-shoe camp arguing you shouldn't wear anything between your foot and the ground at all. Neither is right, and here's the mechanism that explains why — plus the evidence for it.

The ground changed. Your anatomy didn't.

The human foot evolved moving over dirt, gravel, and uneven natural terrain — surfaces firm enough to load against, but irregular enough to deform slightly and let the ankle's joints move through their full range. Most walking surfaces today are flat, rigid, and unyielding: concrete, tile, warehouse decking, asphalt. That shift happened for practical reasons — concrete paving spread through American cities roughly between 1890 and 1930 because it outlasted dirt, wood, and loose stone, not because anyone studied what it would do to the joint below your ankle.

A body built for one environment, dropped into a very different one, with health costs attached — that pattern has a name in evolutionary biology, "evolutionary mismatch," most associated with Harvard's Daniel Lieberman (The Story of the Human Body, 2013), who lists flat feet alongside conditions like type 2 diabetes and lower back pain as examples. It's a framework, not a controlled trial with feet as the variable — Lieberman's own supporting examples (diet, sitting, artificial light) are separate literatures, each with their own evidence base. This is the environment Protalus is designed against: not your foot, the floor.

Why the ankle doesn't move in a straight line

Every step you take, your shin bone twists a little — more on uneven ground. The joint right where your leg meets your foot is basically a hinge: it moves your foot up and down, and it's not built to handle that twist. One joint below it — the subtalar joint, or STJ, just under your ankle — is. Its bones meet at a diagonal, not a straight line: about 42° one direction, 16° another, first mapped out in 1941. That angle is what lets it take a twisting force and turn it into foot motion, and take load coming up from the ground and turn it back into a twist your leg can absorb. Nothing else in your foot does that job. If it can't happen there, the twisting force doesn't disappear — it backs up into your knee.

A flat, symmetric floor asks that joint to sit straight, like its axis ran vertically. It doesn't. The diagonal angle above — and what it means for how the foot rolls in and out as force moves through it — is documented anatomy (Manter, 1941; Kirby, JAPMA 1989 and 2001), not a Protalus theory. Protalus's heel cup is asymmetric — shaped to match that angle, rather than flat or wedged in one direction — as an engineering response to that geometry. Whether an asymmetric heel cup is the one correct way to address it, versus one valid way among others, hasn't been settled by a study that tests shapes against each other; it's a design conclusion drawn from the anatomy above, not itself a separately measured result.

Only your own neuromuscular system can actually do the STJ's job in real time — no external device does that job for you. What a device can do is set the boundary the joint operates inside of. That's the difference between "support" and what Protalus calls guiding motion: a rigid wedge fixes the joint's position and blocks that job outright, which is what the atrophy data below is evidence of. A heel cup shaped to the joint's angle is intended to work differently — as a boundary the joint can't rotate past, not a position it's locked into. The joint still does its own work; the range it's allowed to do that work in is what's being controlled. That's a meaningful mechanical distinction, but it rests on Protalus's own design intent — no independent study has measured whether the heel cup behaves as a boundary versus a lock in practice.

The insole aisle, categorized

"Insoles" and "inserts" mean the same thing. They're not all solving the same problem, though.

Cushioned insoles (foam, gel) absorb shock. They don't change how your foot is aligned — they pad it. Foam also compresses under repeated load, so the padding itself degrades over weeks.

Rigid arch supports don't guide the STJ — they block it. A hard wedge under the arch fixes the foot's position outright rather than letting that joint do the twist-absorbing job explained above. A 2020 study in Clinical Biomechanics followed 18 adults with flexible flatfoot through 12 weeks of custom rigid orthotic use and found a measurable decrease in the size of several intrinsic foot muscles — the flexor digitorum brevis, abductor digiti minimi, and abductor hallucis — consistent with disuse atrophy, while muscle activity during gait stayed the same. That's consistent with what you'd expect if a device took over work the muscles and joint used to do themselves: the study covered rigid orthotics as a category, not any specific branded product, but it's real evidence for a real mechanism, not a marketing assertion.

Custom orthotics, molded by a podiatrist, are the most individualized option and work well for many people — but they run a few hundred dollars and can feel rigid for anyone training or playing sport.

Single-plane corrective insoles, like PowerStep's Pinnacle Maxx line, use a medial post — a wedge that tilts the heel platform in one direction. This is a legitimate, decades-old approach in podiatric orthotics. It corrects one direction of tilt. Because the STJ's axis runs on a diagonal, not a straight line, fully correcting it involves motion in more than one direction at once — though no independent study has directly compared the two approaches head-to-head.

What the lab data actually shows

In 2019, Protalus commissioned an independent biomechanics lab, BioMechanica LLC (Dr. Martyn Shorten, PhD), to measure rearfoot alignment during gait across 31 subjects wearing different insoles. It was commissioned by Protalus and has not been peer-reviewed or published in a journal.

The measurement: how many of the 31 subjects landed within the biomechanically correct subtalar joint range while wearing each product.

Product	Subjects in correct range (of 31)
Protalus M-100	28
Protalus T-100	19
Superfeet	6
Standard EVA insole	3

That's the subject count Protalus reports, not a converted percentage.

Some limits on all of this

• The literature doesn't support cushioned insoles as a cause of bunions; the research points to narrow toe boxes, heel elevation, and genetics instead. The disuse-atrophy finding above is about rigid orthotics, a different category.
• No study has measured Protalus against a stopwatch or force plate for running economy or power output. The plantar fascia and arch do store and return elastic energy during gait (Ker et al., 1987, Nature; Behling et al., 2023, Biological Reviews), and the inference that unrestricted arch motion preserves that function is drawn from that mechanism — it hasn't been tested as a performance claim for this product.
• Protalus is FDA registered. Insoles are FDA Class I, the lowest device-risk category, where registration is a listing requirement rather than a premarket safety review. That's a different thing than "FDA approved" or "FDA cleared."

So, no — you don't need insoles. You need a shield.

Before buying anything in that aisle, ask what it's actually doing to the joint that has to do this work — not just whether it feels supportive. "Support" that blocks the STJ's motion outright is solving the wrong problem: your body is the only thing that can actually manage balance and rotation transfer. A rigid device that takes that job away from it isn't neutral, it's a trade-off, with the atrophy data above as one measured cost of that trade. Padding the mismatch doesn't fix it either — it's still your foot meeting flat ground, just with a softer layer in between.

A shield works differently: it doesn't touch your foot's mechanics directly, and it doesn't take over the joint's job. It changes what's under you — the surface geometry your foot is actually loading against — so the STJ can do the twist-absorbing work it's built for instead of fighting a flat floor to do it. Protalus's T-100 is built around that principle, with the lab data above as the evidence for where its boundary lands. That's also why you don't need a lab to tell you whether it's working for you: your own body is doing the job either way, and you can feel whether something is helping it or getting in the way within the first few steps. If you're not sure your issue traces back to this, that's worth figuring out before you spend anything.