Glossary of Terms

The worlds of natural foot health and functional footwear are filled with industry-specific terms that are frequently used but sometimes not fully understood or appreciated. In the years since we’ve been doing this work, we’ve seen concepts such as “minimalism,” “wide toe box footwear,” and “toe splay,” among others, become more widely adopted and shared, which is wonderful, because it means that natural foot health awareness is growing. The problem is, though: Some companies out there are using these increasingly popular “buzzwords” to market products that don’t actually fit the description, which can be confusing for consumers who are hoping to build stronger, more resilient feet.

We thought it would be helpful, then, to publish a glossary of terms that definitively describes the most commonly-used words, phrases, and concepts in the fields of natural foot health and functional footwear so that you can gain a deeper understanding of these industries and what they have to offer. You’ll find many of the terms listed here sprinkled throughout our website, in our educational articles and product descriptions. Other terms listed here describe aspects of conventional foot care treatments, which we felt were important to include because defining them helps to better illuminate the differences between natural and conventional approaches to feet, footwear, and foot health.

So, with that being said, here are the key terms you’ll want to know if you’re diving into the worlds of natural foot health and minimalist footwear:

1. Anatomical Terms

Forefoot Fat Pad:Sometimes called the “pedal” fat pad, the forefoot fat pad is a thick (~1-2 cm) layer of closely-packed fat cells surrounded by fibrous tissue that, under ideal conditions, is situated on the sole of the foot, beneath the ball of the foot. It is tasked with protecting sensitive ball of foot structures and tissues, including nerves, blood vessels, tendons, ligaments, and bone, and it does this by providing natural cushioning to minimize impact, pressure, friction, and shear forces on the foot. The forefoot fat pad helps you comfortably perform a wide range of weight-bearing activities, such as walking, running, or even standing still.

Hallux:The medical or anatomical term for the big toe.

Intrinsic Foot Muscles:Also known as “plantar arch muscles,” intrinsic foot muscles are a group of muscles that originate at the heel bone and attach to the toes (and so therefore exist entirely within the confines of the foot). Intrinsic foot muscles are responsible for stabilizing the foot and supporting the arches to maintain foot structure. These muscles also assist the actions of the muscles of the lower leg in producing fine motor movements of the toes.

Lateral Longitudinal Arch:The lateral longitudinal arch, which is the flatter of the foot’s two longitudinal arches, runs along along the outside aspect of the foot, contacts the ground in the standing position, and incorporates the following bones: Calcaneus, cuboid, and the 4th and 5th metatarsal bones. The lateral longitudinal arch serves as a support structure for the foot and helps transmit the forces of body weight.

Medial Longitudinal Arch:What we frequently refer to as the “main foot arch,” the medial longitudinal arch, which is the taller of the foot’s two longitudinal arches, runs along the inside aspect of the foot and incorporates the following bones: Calcaneus, talus, navicular, all three cuneiforms, and the first three metatarsals. The medial longitudinal arch plays a crucial role in weight bearing, shock absorption, and propulsion.

Transverse Arch:The transverse foot arch runs across the foot, on the underside of the forefoot, and incorporates the following bones: Cuboid, all three cuneiforms, and the bases of the five metatarsal bones. These bones are bound together by the deep transverse metatarsal ligaments. In addition to weight bearing, the transverse arch is intimately involved in locomotion and balance, and it also provides much of the foot’s necessary “stiffness.”

2. Correct Toes-Related Terms

Bridge:The relatively thin part of a toe spacer that spans the gap between two pylons, both above and below the toe.

Cavity:The hole in which shims can be placed. Each individual Correct Toes toe spacer incorporates two cavities: One in the first pylon, and one in the fourth pylon. The cavities built into Correct Toes can also be used in combination with toe loops.

Durometer:An instrument for testing the hardness of various materials. The Correct Toes device, thanks to extensive testing during the development phase of manufacturing, possesses the optimal durometer hardness/softness, which allows the spacers to be both flexible (i.e., comfortable) and durable (i.e., long lasting).

Medical Grade Silicone:Silicone that is tested for biocompatibility (how biomaterials interact with the human body) and that is appropriate for medical applications. Correct Toes toe spacers are made of medical grade silicone, and they are, therefore, inert, hypoallergenic, non-toxic (to both humans and the environment), and extremely versatile, comfortable, and durable.

Nub:The semi-rounded part of a pylon that projects toward the base of the toes (when the device is worn on the toes). Each individual toe spacer possesses at least two nubs.

Pylon (aka Pillar):The vertical silicone post that separates the toes. Each individual toe spacer incorporates four pylons.

Shim:A rectangular piece of soft material that’s placed into one or both cavities of a spacer. Shims can be helpful additions for those who need a bit more spacing between the toes than the spacer alone can provide (i.e., shims help “bulk up” the spacers to enhance toe splay). Small pieces cut from an old shoe liner or insole, or another conforming piece of silicone, tend to work best as shims. In some cases, it can be helpful to use a pair of tweezers to pull the shims into position, especially if more than one shim is added to a given cavity.

Toe Loop:A thin velcro strap or band that can be looped through a cavity in the device and around either the 1st or 5th toes to help keep the spacers on bare toes, if need be.

Toe Slot (aka Interspace):The openings in the device that accommodate the toes. There are three toe slots, or interspaces, built into the Correct Toes device.

3. Foot Health Concepts

Artificial Arch Support (aka Arch Props, Arch Bumps):Any material or device, usually a conventional arch orthotic or a contoured shoe footbed, that attempts to “prop up” the foot’s medial longitudinal arch. Artificial arch support is often prescribed under the erroneous assumption that the foot is inherently flawed, and that it requires an intervention of this type in order to preserve its integrity or improve upon its function.

Foot Rehabilitation:The process of using natural techniques and approaches to restore the foot to its original state. True foot and toe rehabilitation is an often years-long journey to undo the damage caused by conventional footwear and build optimal foot form, function, alignment, and strength. The foot rehabilitation process typically incorporates a variety of natural foot care strategies and involves a comprehensive approach to foot and toe recovery.

Natural Arch Support:The use of natural techniques to enable the main foot arch (i.e., the medial longitudinal arch) to support itself. In order to achieve natural arch support and promote optimal “loft” in this arch, the foot must be allowed to rest or function on a level surface and the toes must be allowed (or encouraged, if necessary) to splay.

Natural Foot Care:A healthcare discipline that may be practiced by various types of practitioner, including chiropractors, naturopaths, physical therapists, podiatrists, or other manual medicine providers, and that involves natural, noninvasive approaches to address or prevent common foot and toe problems. The field of natural foot care draws from the wisdom of barefoot cultures around the world and from luminaries in the field of podiatry, such as Dr. William A. Rossi and Dr. Ray McClanahan.

Optimal Foot Health:The ultimate goal of the foot rehabilitation process. Optimal foot health is a state in which an individual has realized the full potential of his or her feet to be the strong, sturdy, and reliable foundation that his or her musculoskeletal system requires. Optimal foot health means that the feet are capable of standing up to all of life’s physical challenges without experiencing any of the foot pain or problems that are so prevalent in our shod society.

Proactive Care:The deployment of preventative strategies to thwart potential foot problems before they arise. Proactive care may involve any number of natural foot care approaches, including (but not limited to) the adoption of foot-healthy footwear, the use of Correct Toes toe spacers and other helpful footgear, and the performance of key foot stretching, strengthening, and mobility exercises.

Shoe Liner Test:A quick and simple test to determine the suitability of a given shoe, boot, or other type of footwear. The Shoe Liner Test, which involves the careful examination of a shoe’s liner or insole—and how the foot is situated upon it—is an important measure of how foot-healthy a shoe is and whether or not the shoe will accommodate natural toe splay (including when enabled by Correct Toes).

Synergistic Foot Health Benefits:The summation of beneficial effects to overall foot health that occurs when multiple pieces of footgear are used simultaneously and in a weight-bearing situation. Synergistic foot health benefits may include things such as a quicker-than-expected reduction in pain or discomfort, improved athletic performance and resistance to ankle sprains, or the unexpected restoration of a fallen foot arch, to name just a few among many.

Toe Splay:The degree to which the toes splay, or spread, apart. Optimal toe splay occurs when the toes are perfectly aligned with their corresponding metatarsal bones. Most conventional shoe wearers require a toe spacing device, such as Correct Toes, to restore optimal toe splay and toe function.

Transitioning:The process of switching from conventional footwear to footwear that truly respects the natural shape and function of the human foot. Transitioning is often a multistep process and may take some time, depending on the foot health status of the individual making the transition and how long he or she has relied on conventional footwear. In some cases, it can be helpful to adopt a “transitional” shoe for a period of time before eventually moving on to a more minimalist shoe that builds maximum foot health and robustness, which is, for most, the ultimate goal of transitioning.

4. Footgear-Related Terms

Correct Toes:A revolutionary toe spacing device made of medical grade silicone that gently realigns the toes in their intended anatomical position; that is, in line with their corresponding metatarsal bones. Correct Toes can be worn on bare toes, over a pair of toe socks, and within a pair of sufficiently wide toe box footwear. This toe spacing device is also highly customizable and can easily be tailored to suit unique sets of feet and toes.

Foot Gym:A collection of devices/tools and exercises that can be used or performed at home or at work (or elsewhere) on a daily basis to actively improve toe, foot, ankle, and lower leg strength, stability, balance, flexibility, and range of motion. Also, a “pre-habilitation” concept that seeks to enhance overall musculoskeletal function, prevent injuries, and empower the user in their quest for optimal foot health. Foot gym adopters frequently subscribe to the notion of “antifragility” and use these tools and exercises to build not only the kind of feet that resist all manner of degradation, but also feet that actually benefit from or are strengthened by the physical stressors and challenges they encounter.

Metatarsal Pads:Metatarsal pads are small, unobtrusive pads that are positioned just behind the ball of the foot, in the pocket of space that exists just behind the metatarsal heads. Metatarsal pads help enhance foot comfort, spread the metatarsal heads (to aid the passage of sensitive nerves and blood vessels), straighten and realign crooked toes, restore optimal forefoot fat pad positioning, and address and prevent common foot & toe problems. There are two main types of metatarsal pad: Stationary (i.e., affixed inside the shoe) and mobile (i.e., worn on the foot itself).

Natural Footgear:A set of foot products (footgear) that offer the user the possibility of profound and enduring foot health benefits through natural and noninvasive means. Also, the name of our company!

Proprioceptive Insoles:Thin, flexible insoles that incorporate a firm, textured, small nerve proprioceptive material that's designed to improve posture, enhance movement, and prevent injuries, among other benefits. These innovative insoles allow the user to tap into the power of his or her nervous system and can be used for a variety of purposes, including neurological rehabilitation, athletic performance, and general wellness.

Toe Spacers (aka Toe Separators, Toe Spreaders):The general name for an entire category of products that seek to realign the toes, and of which Correct Toes is the gold standard. Indeed, there are many different types of toe spacers available to consumers, but these options vary considerably in terms of comfort, quality, durability, and effectiveness. Toe spacers are most effective (i.e., they have their greatest corrective effect) when they are worn inside footwear that can comfortably accommodate them and during weight-bearing activities that impart forces through the joints and tissues of the toes.

Toe Socks:Socks that possess individual toe sleeves and that afford the toes freedom of motion. Toe socks, especially when used in combination with Correct Toes toe spacers, promote optimal toe splay, and they help address a variety of crooked toe problems, including bunions, hammertoes, and overlapping toes. Toe socks also help reduce the likelihood of blisters between the toes, which is helpful for runners and other athletes, and they promote proper balance, stability, posture, and toe dexterity.

5. Footwear-Related Terms

Anatomical Toe Box:A toe box that closely mimics the shape of a truly healthy human forefoot. An anatomical toe box easily accommodates the entire forefoot, including all five toes in their optimal splayed configuration.

Barefoot Shoes:A subset of foot-healthy footwear that is ultraminimalist, to the point where the feel of the shoes is almost akin to being barefoot, but with a thin layer of protective material between the foot’s sole and the ground. Barefoot shoes are most suitable for experienced users of minimalist or functional footwear and those who have already developed strong, resilient feet.

Conventional Footwear:Footwear that is characterized by a number of injurious design elements, including (but not limited to) tapering toe boxes, heel elevation, toe spring, rigid soles, excessive cushioning, excessive weight, and (often) built-in arch “support” and motion control. The prolonged use of conventional footwear is the No. 1 cause of most common foot and toe problems in shoe-wearing societies.

Cushioning:The amount of shock-absorbing material that exists in the sole of a given shoe. In general, and perhaps somewhat counterintuitively, less is more when it comes to shoe cushioning. Indeed, the more cushioning a shoe possesses, the harder on and more damaging to the joints it may be. For most people, there is an optimal range of shoe cushioning that is far less than what is touted by the footwear industry.

Flexible Soles:A foot-health-positive design feature incorporated into minimalist footwear that encourages the foot to become strong on its own. In order for a shoe’s sole to be flexible, you must be easily able to bend, twist, or fold the shoe in half, or you must be able to easily roll the shoe into a ball; these are all indications that the shoe’s sole has sufficient flexibility to let the foot function and develop naturally.

Foot-Healthy Footwear:Footwear that fully considers the form, function, and needs of the human foot. Foot-healthy footwear provides the toes with ample room in which to splay, places the entire foot on a level plane, possesses a relatively thin and highly flexible sole, is lightweight, and does not attempt to control the motion of the foot in any way. The term “foot-healthy footwear” is nearly synonymous with “minimalist footwear” and “functional footwear,” but is, perhaps, more aspirational and represents the true pinnacle of what footwear can be from a foot health and performance standpoint.

Functional Footwear:Footwear that allows the foot to function as nature intended. Functional footwear, a term often used interchangeably with “foot-healthy footwear” and (in some cases) “minimalist footwear,” provides an unobtrusive environment for the foot and toes to operate, does not encroach upon the forefoot in any way, and promotes the development of strong, sturdy feet with each and every footfall. Functional footwear is flat and flexible in the sole, lightweight in design, has a low stack height, and is widest at the ends of the toes. It's important to note that functional footwear can be, but isn't always, minimalist, and that minimalist footwear can be, but isn't always, functional.

Ground Feel:The ability, while wearing a given pair of shoes, to sense the ground or terrain beneath the feet. Minimalist footwear, with its relatively thin and flexible soles, typically confers excellent ground feel to the user, which is helpful in providing the brain with the necessary information (i.e., tactile feedback) to make safe and conscientious footfalls. Thicker-soled footwear tends to blunt ground feel and put the user at risk for increased joint loads and errant or injurious footfalls.

Healthy-Foot-Shaped Footwear:Footwear that is shaped like a healthy human foot. In order to be “healthy-foot-shaped,” a given shoe must have an anatomical toe box and be able to accommodate a foot in its natural state; that is, with toes fully splayed and in line with their corresponding metatarsal bones.

Heel Elevation:An injurious design element present in almost every conventional shoe, from dress shoes to work boots to running shoes. Heel elevation involves a layer of material (ranging from stiff to spongy) that elevates the heel above the forefoot. Heel elevation (especially in combination with toe spring) causes an unnecessary stretching of foot structures, forces the wearer to walk on a downhill ramp, puts extraordinary pressure on sensitive ball of foot tissues, and essentially inverts the main foot arch.

Last:A 3-dimensional wooden or plastic mold around which a shoe is constructed. Last shapes vary from one shoe company or brand to the next (and sometimes even between different models within the same brand).

Level Support Platform:A completely flat surface, from heel to toe, upon which the foot may rest or act. A level support platform is important in enabling natural arch support and in creating a stable foot/ankle complex. A level support platform is an important inclusion in any shoe that purports to be foot-healthy.

Lightweight:A shoe, boot, sandal, or other type of footwear that is constructed to be as lightweight as possible. Lightweight shoes, which often incorporate a breathable upper, offer the possibility of a lighter step (i.e., reduced joint impact) and a more natural gait. A lightweight design is one of the hallmarks of foot-healthy footwear.

Maximalist Footwear:Footwear (often athletic, though sometimes casual as well) that incorporates significant padding or material under the foot’s sole. Maximalist shoes go far beyond simply protecting the foot’s sole, placing an excessive amount of material between the foot and the ground. Any shoe that possesses this degree of padding strips the foot of its ability to sense the ground, unfavorably alters gait, and encourages excessive joint loading. Most maximalist shoes also incorporate a quartet of injurious design characteristics, including heel elevation, toe spring, tapering toe boxes, and rigid, inflexible soles.

Midsole:A layer of material, often shock-absorbing EVA foam, that exists between the inner and outer soles of a shoe.

Minimalist Footwear:The most common name for an entire class of footwear that seeks to let the foot function in a natural way. A true minimalist shoe is no more (or no less) than a protective covering and ornamental dressing that allows the foot to perform like a bare foot inside the shoe. A foot-health-positive minimalist shoe possesses a sufficiently wide toe box to allow for natural toe splay, a completely flat sole from heel to toe to enable natural arch support, a sole that can easily be bent or twisted in multiple directions to encourage increased foot strength, an overall lightweight design to promote a more natural gait, and a low stack height to confer optimal ground feel. It's important to note that some minimalist shoes may possess a tapering toe box, so while they may be minimalist in many important ways, they may not actually be functional or foot-healthy.

Motion Control:Elements incorporated into some conventional shoes that (erroneously) attempt to dictate or control the foot’s movement. Some footwear incorporates built-in “arch support,” which often takes the form of arch props or bumps that are intended to fill the space beneath the main foot arch to control pronation or address a variety of foot ailments. Some shoes also incorporate sole material or a sole design (e.g., grooves or channels) that attempt to “augment” or “correct” the motion of the foot. A foot-healthy shoe does not possess motion control elements.

Outsole:The outermost sole layer of a shoe, boot, or other type of footwear. The outsole is the portion of the shoe that is in contact with the ground.

Rigid Soles: A common inclusion in most conventional footwear that effectively immobilizes the foot in a compromised and deformed configuration, both during activity and at rest. Rigid soles hinder the foot’s propulsive ability, contribute to immediate and long-term foot, ankle, and other musculoskeletal problems, and increase the likelihood of injury from poor foot placement due to decreased tactile sensation.

Stack Height:The amount of shoe material between the foot and the ground. This number, usually reported in millimeters (mm), is the sum thickness of a shoe's insole, midsole, and outsole.

Tapering Toe Boxes:The narrowing of a shoe’s toe box from the ball of the foot out to the ends of the toes. Tapering toe boxes force the toes into a wedge position that compromises foot health, form, and function, and they are one of the most harmful (and ubiquitous) features found in conventional footwear. Tapering toe boxes are the antithesis of anatomical toe boxes.

Transitional Shoe:A shoe that helps aid the process of transitioning from conventional footwear to minimalist footwear. After a lifetime of wearing thick-soled shoes, the sole of the foot (including the skin, muscles, nerves, and other tissues that make up this part of the body) may not be not properly adapted to the ground, and being barefoot or using thin-soled shoes may be uncomfortable for some. The best way to build up or condition the foot’s sole, then, is to start with slightly thicker-soled footwear and then move to thinner-soled options over time. A foot-health-positive transitional shoe should still possess a flat support platform (i.e., no heel elevation, no toe spring, and no arch-propping inserts), a toe box that's widest at the ends of the toes, a relatively flexible sole that can be bent or twisted, and a low overall weight.

Toe Box:The part of a closed-toe shoe or boot that houses the toes. In a truly foot-healthy shoe, the toe box should not encroach on any aspect of the toes and should, in fact, allow the toes to splay and articulate naturally. An anatomical toe box closely mimics the shape of a natural human forefoot and can comfortably accommodate Correct Toes toe spacers.

Toe Spring:A toe-deforming shoe element present in most conventional footwear. Toe spring is the elevation or ramping of a shoe’s toe box above the ground or support surface. The current industry standard for toe spring for most types of footwear is 15 degrees. There are two main types of toe spring (rigid vs. flexible), with rigid toe spring being far worse for the foot than flexible toe spring. Some minimalist shoes contain flexible toe spring, which is usually easily compressed out when weight bearing.

Upper:The portion of a shoe that covers the sides and top of the foot. An upper is affixed to a shoe’s sole and may incorporate the following elements: Vamp, toe box, tongue, eyelets, throat, puff, quarters, heel counter, backstay, and linings.

Wide Toe Box:A toe box that is widest at the ends of the toes (where maximum width is required for optimal toe splay and foot health) and not simply wide at the ball of the foot. A truly foot-healthy shoe is wide at the ball of the foot and then continues to get even wider out toward the ends of the toes. Some conventional shoes may be sufficiently wide at the ball of the foot but then taper to a point at the ends of the toes, which can lead to a variety of foot problems.

Zero Drop:An industry term that describes a completely flat sole from heel to toe. Zero drop footwear allows the foot to rest and function on a level plane, encourages optimal foot and ankle stability, promotes balance, helps prevent overpronation, and allows the foot’s arches to function naturally.

6. General Terms

Conservative Care:An approach to healthcare that emphasizes natural, noninvasive, and nonsurgical treatment options that seek to bolster the body’s inherent healing capabilities. The term “conservative,” at least in the context of treating foot pain and problems, does not necessarily mean the opposite of aggressive treatment, but rather, implies that any treatment provided will, at its core, respect the philosophical approach of “first, do no harm.”

Conventional Foot Care:A system of foot care practiced by the majority of podiatrists that relies on the use of drugs, surgery, orthotics, motion control footwear, and other invasive measures to address the symptoms of various foot problems. Conventional foot care assumes that the foot is inherently flawed and incapable of supporting itself.

Foot Health Heritage:The idea that we are all (by and large) born with perfect feet and that, with the proper care and attention, we can experience the same foot robustness enjoyed by our unshod ancestors and barefoot cultures around the world. The term “foot health heritage” implies that optimal foot form and function is a birthright and that we, collectively, as a species, have the potential—and perhaps the obligation—to realize longlasting foot and musculoskeletal health.

Foot Health Positive:Any aspect of footwear or foot care that advances the cause of feet in a healthy, foot-forward way.

Overpronation:Also known as “excessive pronation,” overpronation occurs when the big toe is forced to deviate from its intended position in line with the 1st metatarsal bone (usually caused by the wearing of conventional footwear), leading to an inward collapse of the foot and ankle and, possibly, a variety of subsequent musculoskeletal problems.

Pronation:The combination of three separate actions in the foot and ankle, including subtalar eversion, ankle dorsiflexion, and forefoot abduction. A certain degree of pronation is normal and natural when walking or running.

Supination:The combination of three separate actions in the foot and ankle, including subtalar inversion, ankle plantar flexion, and forefoot adduction. A certain degree of supination is normal and natural when walking or running.

Shod:An individual or group of people who wear footwear.

Unshod:An individual or group of people who do not wear footwear or who wear only minimal footwear.