A PATENTED FOOTBED BACKED BY SCIENCE

Engineered to Support the Biomechanics of Your Feet

What We Know About How Your Feet Work

The Flex 3 Fulcrum footbed was designed in support of established research in foot biomechanics. This page lays out that research and explains how it shaped our design.

To be clear, the information and studies referenced below examine how feet work. They are not studies of pushpül slides. Where we share what a study found, we are describing the mechanism it investigated, not making a claim about what our product does for you.

> > > TLDR: Your feet contain a lot of small muscles that most footwear, including so-called recovery slides, ignore. Our patented footbed is designed to stop ignoring them.

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What Are the Intrinsic Muscles of the Foot?

What Are the Intrinsic Muscles of the Foot?

The intrinsic muscles start and end inside the foot. That distinguishes them from the extrinsic muscles, which start in the lower leg and send tendons down into the foot to handle the bigger work of pointing and flexing.

There are roughly twenty intrinsic muscles in each foot, layered across the sole and the top. Individually they are small and weak. Together they handle the fine work: spreading and gripping the toes, adjusting the arch, and making the constant micro-corrections that keep you balanced on uneven ground.

...and Why They Matter

  • Steady Balance
    Foot muscles adjust continuously as your weight shifts, keeping you upright on a trail, on a gym floor, or standing on one leg.
  • Arch Control
    They also contribute to how the arch behaves under load, alongside the passive tissues that help hold its shape.
  • Sensory Feedback
    Active, healthy foot muscles send more messages to your nervous system to better inform balance and coordination.

How to Strengthen Intrinsic Foot Muscles

Below are four approaches, roughly in order of how much they are worth your time:

(Tricky) Foot Exercise. Sit with your foot flat. Without curling your toes, draw the ball of your foot toward your heel. Hold a few seconds. This is the standard starting point.

Spread Your Toes. Every chance you get, spread your toes apart and hold. Harder than it sounds. Most people have to work at it before anything moves independently.

Walk Barefoot. Walking barefoot on varied surfaces - grass, sand, uneven ground - works the foot and provides sensory input. Build up slowly if you've spent years in cushioned shoes.

Textured Footwear. A contoured footbed keeps foot muscles working. It does not replace the exercises above. It is a way of getting some of the same input without setting time aside for it.

That last one is where we fit. The message is: engage and activate your feet any and every way you can.

More Foot Fitness Tips
What Is the Windlass Mechanism?

What Is the Windlass Mechanism?

The windlass mechanism describes how the foot stiffens itself for push-off. When your toes bend upward at the end of a step, the plantar fascia, the thick band of tissue running from heel to toes, is drawn tight around the joints at the base of the toes. That tension pulls the heel and the ball of the foot toward each other, and the arch rises.

This biomechanical effect turns a flexible foot into a more rigid structure at exactly the moment you need to push off, propelling your body forward. In this process, your foot first stores then releases elastic energy, reducing the muscular effort required to walk or jump or run.

British orthopedic surgeon J.H. Hicks described this in the Journal of Anatomy in 1954. Working with both living subjects and cadavers, his notable finding was that the arch rose even in feet with no muscle activity at all, which showed the mechanism is built into the structure of the foot rather than something muscles have to initiate.

(FYI: The term "windlass" comes from sailing and describes a cable system that winds a rope around a drum.)

Research since has refined the picture. The windlass analogy explains arch behavior in static and passive conditions. During actual walking and running, the relationship between toe extension and arch recoil turns out to be governed by passive tissues and active muscles working together, which is why current work tends to describe the arch as a dynamic lever rather than a rigid one.

How this shaped the design. The Low-Rise Arch in the Flex 3 footbed is deliberately low. A high, rigid arch would otherwise hold the foot in a fixed position. The goal is to support the arch without preventing the movement the foot's windlass mechanism depends on.

[Hicks, J.H. (1954). "The mechanics of the foot. II. The plantar aponeurosis and the arch." Journal of Anatomy, 88(Pt 1), 25-30.]

Research, Insights and What We've Learned

Kogler, Solomonidis, and Paul studied how different arch support designs affect strain in the plantar fascia, using cadaveric foot models loaded to simulate standing. They found contour matters more than height: supports shaped to follow the curve of the arch, particularly under its highest point, reduced strain measurably; supports that simply raised the foot did not.

It’s worth noting the research limitation, which the authors raised themselves. This was bench work under a simulated quiet stance, not measurement of living people walking. It tells us about the mechanics, not the outcomes.

+ How this shaped our design. As noted above, contour outranks height. The Low-Rise Arch follows the arch rather than propping it up.

[Kogler, G.F., Veer, F.B., Solomonidis, S.E., & Paul, J.P. (1999). "The influence of medial and lateral placement of orthotic wedges on loading of the plantar aponeurosis." The Journal of Bone and Joint Surgery. American Volume, 81(10), 1403-1413.]

The metatarsals are the five long bones running from the middle of the foot to the base of the toes. Inside most closed shoes they sit compressed together, and the heads of those bones take a concentrated load at push-off.

The established mechanical principle is that a raised pad placed just behind the metatarsal heads moves that load off the heads and onto the shafts of the bones, spreading pressure across a larger area instead of concentrating it at a few points.

+ How this shaped our design. The Meta Pad sits behind the metatarsal heads for exactly this reason, and the footbed is wider than a standard slide so the metatarsals have somewhere to spread into.

The Heel Ball is the easiest of the three to explain, because it doesn't need a study. It's also the easiest one to feel.

Applying sustained pressure to soft tissue is what a massage ball does, what a foam roller does, and what a therapist's thumb does. The Heel Ball is a fixed version of the same mechanical action, positioned under the heel where the plantar fascia attaches, engaging as you walk rather than requiring you to stop down and work on it.

+ How this shaped our design. This is the first feature we explored, because it's the most common pain point. It's also the anchor of our footbed design. The way your foot hits the Heel Ball also determines your placement over the Meta Pad and Low-Rise Arch.

US Patent 12,011,066

What We Pulled From Field Testing

  • Get a Response
    Give your feet something to feel and respond to rather than a flat surface that asks nothing of them.
  • person walking up brick stairs in Flex 3 Fitness Slides Follow the Shape
    Shape the footbed to follow the foot for more natural support rather than rigidly propping it up and overcorrecting.
  • Share the Load
    Distribute pressure across the entire footbed instead of under the ball and heel. And give the toes some room.
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FAQ: Some More About Foot Muscles

Each foot has roughly twenty intrinsic muscles, which start and end inside the foot, plus the tendons of about twelve extrinsic muscles originating in the lower leg. Counts vary slightly between anatomical references depending on how some muscles are grouped.

It depends what you are asking them to do. As comfortable footwear for after training, most people find them worth owning. But if you're looking to train your feet and improve their resilience, the pushpül Flex 3 footbed is shaped to keep your foot working while you wear it, which is a different goal from cushioning. Whether that suits you comes down to what you want out of the hours after a session.

Inward rotation, called inversion, is driven mainly by the tibialis anterior and tibialis posterior, both extrinsic muscles originating in the lower leg. The intrinsic muscles contribute to the finer adjustments that go with it.

Partly. Walking barefoot on varied surfaces and wearing contoured rather than flat footwear both give the foot more to respond to. Neither replaces deliberate work like the short foot exercise, but both add input across hours rather than minutes.

The Ultimate Foot Fitness Tül

The Ultimate Foot Fitness Tül

For dedicated athletes who understand recovery isn't rest. It's another training session. Get Your Feet Fit

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Cited Sources

Hicks, J.H. (1954). "The mechanics of the foot. II. The plantar aponeurosis and the arch." Journal of Anatomy, 88(Pt 1), 25-30.

Kogler, G.F., Veer, F.B., Solomonidis, S.E., & Paul, J.P. (1999). "The influence of medial and lateral placement of orthotic wedges on loading of the plantar aponeurosis." The Journal of Bone and Joint Surgery. American Volume, 81(10), 1403-1413.

Kang, J.H., Chen, M.D., Chen, S.C., Hsieh, C.W. (2006). "Correlations between subjective treatment responses and plantar pressure parameters of metatarsal pad treatment in metatarsalgia patients: a prospective study." BMC Musculoskeletal Disorders, 7, 76.

Espinosa, N., Maceira, E., & Myerson, M.S. (2010). "Current concept review: metatarsalgia." Foot & Ankle International, 31(8), 733-748.

Renan-Ordine, R., Alburquerque-Sendín, F., de Souza, D.P., Cleland, J.A., & Fernández-de-las-Peñas, C. (2011). "Effectiveness of myofascial trigger point manual therapy combined with a self-stretching protocol for the management of plantar heel pain: a randomized controlled trial." Journal of Orthopaedic & Sports Physical Therapy (JOSPT), 41(2), 43-50.

Simons, D.G., Travell, J.G., & Simons, L.S. (1999). Travell & Simons' Myofascial Pain and Dysfunction: The Trigger Point Manual (Vol. 1). Lippincott Williams & Wilkins.

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