For decades, we, as footwear consumers and users, have been told that we need plenty of padding in our shoes and under our feet to help boost comfort and buffer the forces on our bodies that occur during standing, walking, running, and jumping. Like many things in the health arena, this information has become common knowledge and accepted as fact. Shoe industry bigwigs along with countless healthcare professionals have championed this idea and instructed customers and patients to look for a high degree of padding or cushioning when selecting footwear, especially athletic footwear. Perhaps not surprisingly, the current ethos in the athletic shoe industry is to embrace padding and all its purported benefits, even going so far as to suggest that the so-called “maximalist” shoes now available are the next step in the evolution of optimal shoe form and function.
The lens through which we at Natural Footgear view footwear leads us to a very different conclusion about what constitutes truly foot-healthy footwear. This article is our attempt to debunk the idea that excessive shoe cushioning is in any way advantageous, and that it may, in fact, be detrimental to immediate and long-term foot and lower extremity health for many people. As always, we hope to cut through industry myths and provide you with the best possible information to make informed choices. Are we anti-cushioning? No, not per se; there are certain circumstances where some shoe padding may be helpful. What we do take issue with is the notion that more padding necessarily means a safer and healthier shoe for all. But more on that in just a bit.
One of the main points we want to establish in this article is that there are a lot of misconceptions out there about shoe cushioning. The prevailing idea behind shoe cushioning is that a greater amount of padding under the foot will help reduce the impact forces on the body’s joints and tissues during weight-bearing activity. Intuitively, this may seem like a reasonable claim, given that we’ve been told for years that we need cushioning to protect our joints and soft tissues from damage. It’s an easy concept to wrap our minds around. What you may be surprised to learn, however, is that physics and research do not support this claim. In fact, the more cushioning that a shoe possesses, the harder and more damaging on our joints it may be.
To understand why this is so, it’s important to understand the physics of collisions. To start with, the net force acting on an object is:
With a body that has one foot in contact with the ground, there are two vertical forces acting on the body, which are the ground pushing up, traditionally referred to as the Normal Force, which I'll write as N (normal in this context meaning perpendicular to the surface) and the force of gravity pulling down, often expressed as mg, or mass times 9.8 meters per second squared. So we have:
The acceleration is defined as change in velocity divided by time, so using vf as final velocity and vi as initial velocity, and doing some rearranging, we can write this equation as:
So what changes when someone goes from a thickly cushioned shoe to a minimalist shoe or even to being completely barefoot? The real expert in this realm is Professor Daniel Lieberman at Harvard, who has done some really nice studies on impact forces using force plates so that the forces of running shod versus barefoot can actually be quantified. But here is the essence of the argument: With shoe cushioning, our sense of what is going on is dulled (see Shoe Cushioning Issue #1 below for additional thoughts on this topic), and we tend to run with a certain gait—a gait that involves more up and down bouncing as well as feet that reach out more and upon which we essentially fall during the landing phase of gait.
There may be small fluctuations in the time that the foot is in contact with the ground between shod heel strikers and barefoot or minimalist midfoot strikers, which would affect the Normal Force, but the real key here is that the shod, cushioned gait makes both the initial downward velocity and the final upward velocity larger (Note: The above equation is written using the convention that up is positive and down is negative, so the vf is a positive number and the vi is a negative one—meaning when both numbers get larger, the difference between them gets larger). This results in a larger Normal Force, or, in other words, more force that the foot and rest of the body has to deal with. However, when running barefoot or in minimalist footwear, we tend to change our gait. We bounce less, and we tend to make the foot strike happen more underneath our bodies instead of out front. So, instead of falling hard on the foot like we do in cushioned shoes, we control the impact better in minimalist shoes or with our bare feet and make the difference between vf and vi less, thereby reducing the overall force on our feet and bodies.
Below are a couple of examples using real numbers in the force equation to illustrate the above points. For our examples below involving runners, let’s set mass (m) equal to 50 kg. The acceleration of gravity (g) is a constant at 9.8 m/s2. Let’s set the change in vertical velocity (vf - vi) equal to 8 m/s for cushioned shoes and 6 m/s for minimalist shoes or bare feet. For the impact duration, let’s use a value of 0.3 seconds for both cushioned shoes and minimalist shoes.
Note: To better understand the rationale behind the selection of these numbers, please scroll to the very bottom of this article, to the “Appendix: Understanding the Numbers” section, for a more detailed explanation.
Example #1: Force experienced by a runner in cushioned shoes:
Example #2: Force experienced by a runner in minimalist shoes (or with bare feet):
For the sake of comparison, a 50 kg person weighs 490 N in metric units of force, so that first number (for cushioned shoes) is about 3.7 times bodyweight whereas the second number (for minimalist shoes or bare feet) is only about 3.0 times bodyweight. Add that difference up over miles and days, months, and years of running and walking, and you can see why keeping shoe padding to a minimum makes such a huge difference.
It’s true that the physics of collisions is much more complex and detailed than what’s shown above (for example, we’re treating all of the person’s mass as moving up and down at the same speed; in reality, it’s more complicated as the torso obviously doesn't move up and down at the same speed as the feet do), but the equation does demonstrate the point that using cushioned shoes actually equates to greater forces on lower extremity joints and tissues, not less.
Note: If we wanted to get more technical in our calculations, we would take into consideration the fact that the ground reaction force is made up of several vectors in different directions. This would be a more rigorous way of explaining the force of the ground on the foot. The equation I used above captures only purely vertical force, which does make the point about vertical velocity changes in the foot being different between a heavily shod runner and a minimally shod or barefoot runner, but it leaves out the motion of the runner or walker and the foot itself in relation to the moving ground. Landing and takeoff angle would also be a factor here, as would the way in which force moves through the foot. And so on. The point is, a fancier model would still contain the key points demonstrated in the above examples.
Cushioning Issue #1: Joint Impact
What’s true of excessive shoe cushioning is that it’s highly deceptive: It makes us think we’re reducing joint impact because it feels that way, but in fact it’s just reducing the sensation of the impact. According to the laws of physics (as demonstrated above), the impact forces on our joints and tissues actually increase in more highly cushioned shoes. Excessive shoe cushioning can be hugely detrimental to our joints and tissues because it allows us to be sloppy with our footfalls or foot placement, and it allows us to slap our feet down with tremendous force without any perceived consequences.
When we fail to place our feet just right (including in the proper alignment relative to the ground), our weight distribution gets thrown off. The heels, toes, and arches are not able to properly absorb impact and distribute body weight. This can have negative implications for our feet, ankles, knees, back, and so on, all the way up the kinetic chain. By contrast, when we’re barefoot or wearing only thin-soled, flexible footwear, our feet and bodies can feel everything about the ground and what’s happening in our lower extremities. Footfalls tend to be gentler and more mindful, seeking out the smoothest path over which to move forward, and this can have a huge effect on the well-being of our joints and tissues.
Also, doing high-impact activities in shoes with no or only minimal cushioning can, in some cases, feel uncomfortable, but this isn’t necessarily a bad thing because it encourages a reassessment of how we’re performing an activity. Without shoes, landing on the heel can be painful and may result in larger than necessary collision forces. What tends to happen in barefoot people or people who adopt minimalist footwear is that, over time, they will actually develop the ability to move (walk, run, jump, etc.) in a less jarring way. Many people who use minimalist footwear or who go barefoot tend to spread their toes before striking the ground, landing first on the lateral (or outside) aspect of the ball of the foot and then rolling across the ball of the foot until the toe-off phase of gait, in which the big toe leaves the ground last. This footfall pattern helps reduce impact forces during the landing phase of gait.
So, interestingly, and perhaps unintuitively, often the best way for us to reduce joint impact is to reduce shoe cushioning. That said, this approach does require some time, patience, and care. And it tends to work best when our toes are splayed (ideally enabled by Correct Toes) and placed flat on the ground or on a completely flat sole, where each of our toes can bear their fair share of the weight. This development also tends to happen naturally; our bodies figure it out based on the strong tactile and proprioceptive feedback they experience in the minimally shod state.
Helpful Exercise: One illuminating exercise you can perform to observe the difference in impact forces between cushioned and minimalist shoes is to plug your ears with earplugs and then go running, first in cushioned shoes, then in minimalist shoes. You should notice quite a difference in your ears right away, mostly in terms of the jolting and jarring forces your body experiences while running in cushioned shoes.
Cushioning Issue #2: Effort Expended
Another aspect of shoe cushioning that’s often overlooked is the fact that cushioned soles actually force us to do more work with each footfall. The greater the cushioning or sponginess in a given shoe, the less efficiently force is transferred between the foot (the big toe, really) and the ground. Energy that would otherwise go into propulsion is dispersed throughout the shoe’s padding and wasted. It’s a similar effect (though obviously less extreme) to running in sand. In people who ambulate in bare feet or in minimalist footwear, a maximum amount of propulsive energy is transferred between the foot and the ground during the toe-off phase of gait, and considerably less energy is wasted with each step or stride.
Cushioning Issue #3: Foot Muscle Atrophy & Arch Effects
Despite the fact that most conventional shoes, especially athletic shoes, possess springy cushioning under the foot, the relative thickness of the soles translates into greater sole rigidity, which can have detrimental effects on foot muscle strength and arch integrity. As has been said elsewhere on this site and around the web, wearing thickly cushioned, rigid-soled footwear is like putting your foot in a cast and expecting it to get stronger. The relative foot immobilization that occurs in thickly padded shoes prevents foot muscles from doing their fair share of the work and allows them to slowly deteriorate, or atrophy, over time. A muscle that is not used regularly will lose its tone and its ability to generate sufficient force, which can have a significant effect on the function of the foot and the rest of the musculoskeletal system.
Shoes that possess no or only minimal padding and no built-in arch support help enable the foot to do what it’s intended to do (i.e., these shoes make the foot stronger, more flexible, and less susceptible to pain and stiffness). One of the first sensations many people experience after switching from conventional footwear with lots of cushioning to minimalist shoes with no or relatively little cushioning is the sensation of enhanced foot strength. Foot muscles that have long been underutilized begin to awaken, and the feeling of enhanced foot strength quickly becomes apparent. Shoes without excessive cushioning and so-called motion-control technology also help restore a strong and healthy medial longitudinal (ML) arch—the principal arch in our feet. I can tell you from personal experience that my own ML arch is now much more pronounced and defined since I adopted minimalist shoes and natural foot health techniques many years ago.
Cushioning Issue #4: Injury Frequency
One of the most frustrating aspects of the shoe cushioning debate is the notion that less cushioning inevitably means more foot and lower extremity injuries. A lot has been made of the recent class action lawsuit brought against Vibram FiveFingers, but the fact that Vibram settled their case does not suggest that minimalist shoes are injurious, only that Vibram may have gone too far in touting the health merits of their unique product. It’s true that injuries can occur when using minimalist footwear, but these injuries tend to be of the more acute (i.e., temporary) variety and most likely occur when users transition too quickly. Some problems, such as Achilles tendon issues, may be a direct result of the structural changes in the foot and ankle caused by conventional footwear worn over many years.
Indeed, conventional shoes make our feet weak, and so it’s likely that many people who experienced injuries using Vibram FiveFingers shoes weren’t ready to jump into this type of ultra minimalist shoe without a sufficient transition period. It could also be that users didn’t understand that the minimal cushioning was supposed to alter their gait, and that the altered gait is what most affects the equation shown earlier in this article and reduces forces on the body.
What’s easy to forget with all of the media attention surrounding Vibram FiveFingers shoes is that conventional footwear with excessive padding has caused literally countless chronic foot and toe problems over many decades, and that almost everyone who wears conventional footwear will experience some sort of significant foot problem at some point in their lives.
A classic study by Robbins and Waked published back in 1997 in the British Journal of Sports Medicine states the following:
Athletic footwear are associated with frequent injury that are thought to result from repetitive impact. No scientific data suggest they protect well. Expensive athletic shoes are deceptively advertised to safeguard well through “cushioning impact” yet account for 123 percent greater injury frequency than the cheapest ones.
The “cheapest ones” referred to above are shoes with the least cushioning and motion-control “technology” built into them. Robbins and Waked drew the following conclusions from their study:
This is the first report to suggest: (1) deceptive advertising of protective devices may represent a public health hazard and may have to be eliminated presumably through regulation; (2) a tendency in humans to be less cautious when using new devices of unknown benefit because of overly positive attitudes associated with new technology and novel devices.
Some may assume that shoes, especially athletic shoes, are designed by engineers or biomechanics experts to optimize movement while maximizing foot comfort and health. But the reality is that the shoe industry is driven by aesthetics, or by what “looks good” on the shelf, and that little attention and resources are devoted to creating truly foot-healthy products. So, the very shoes that are touted to enhance athletic performance and prevent injuries actually hinder performance and cause injuries by altering natural foot form and function as well as gait. Indeed, nature gave us everything we need to ensure lasting foot health and prevent injuries, as evidenced by this passage from a study published by Michael Warburton in the journal Sportscience:
Running barefoot is associated with a substantially lower prevalence of acute injuries of the ankle and chronic injuries of the lower leg in developing countries [...] Laboratory studies show that the energy cost of running is reduced by about 4% when the feet are not shod.
While going barefoot is not for everyone, finding shoes that allow the foot to act like a bare foot inside the shoe is something that almost all of us can do to ensure long-term foot and lower extremity health, especially now that natural footgear exists to enable this foot health behavior.
Cushioning Issue #5: Knee Problems
Another important consideration in the shoe cushioning debate is the effect of footwear on knee health. When we land on our heels (as almost all runners and walkers who wear cushioned shoes do), our ankles can't help as much in managing impact, so our knees and hips have to handle our bodies’ natural shock absorption. However, as mentioned earlier in this article, barefoot or minimally shod runners tend to adopt a midfoot strike, allowing the ankle to contribute better to shock absorption. With more joints handling the shock, the forces get more evenly distributed between the lower extremity joints.
The relationship between padded shoes and knee problems (specifically, knee osteoarthritis) has been examined more closely in recent years. Conventional medical wisdom states that the following factors may contribute to knee osteoarthritis: Weight, heredity, gender, age, previous traumatic knee injuries, repetitive stress injuries, participation in contact sports, certain health conditions, nutritional deficiencies, and physical deconditioning. While many of these factors undoubtedly contribute to an accelerated rate of articular cartilage loss, the role of conventional footwear in the development of knee osteoarthritis is perhaps the single most important factor in the onset of this health problem. Several reliable and credible sources have produced compelling arguments linking the long-term use of conventional footwear (i.e., padded shoes with tapering toe boxes, toe spring, heel elevation, and relatively rigid soles) with the development or worsening of knee osteoarthritis.
A 2006 Rush Medical College study, conducted by Najia Shakoor and Joel A. Block and published in the journal Arthritis and Rheumatism, examined stress loads on the knees of study participants who wore various shoe types and no shoes at all. The researchers state the following:
It appears that patients with medial knee [the inside aspect of the knee] OA [osteoarthritis] undergo significant reductions in joint loads at their knees and hips when walking barefoot compared with when walking in their normal shoes. Since knee OA is mediated in part by aberrant loading, and since excess loading has been shown to be associated with pain and disease progression, these data suggest that modern shoes may exacerbate the abnormal biomechanics of lower extremity OA.
Shakoor and Block conclude that:
Shoes may detrimentally increase loads on the lower extremity joints. Once factors responsible for the differences in loads between with-shoe and barefoot walking are better delineated, modern shoes and walking practices may need to be reevaluated with regard to their effects on the prevalence and progression of OA in our society.
It's my personal belief, and clearly the belief of the researchers above, that a lot of lower extremity osteoarthritis could be avoided if we were more selective and judicious with our footwear choices.
Harnessing Our Feet’s Natural Protective Mechanisms
Individuals who have gone barefoot or who have worn minimalist footwear their entire lives possess several built-in mechanisms that offer sole protection. The first of these mechanisms is optimal toe splay. Toes that are splayed well apart confer a large degree of protection from the impact forces experienced during weight-bearing activity by spreading the impact forces out over a larger surface area. Conventional shoes force the toes together and elevate the toes above the forefoot, focusing a majority of the impact forces on a much smaller area of the ball of the foot. Correct Toes toe spacers can be worn in shoes with a sufficiently wide toe box to help restore natural toe splay and disperse impact forces over a larger surface area of the foot.
Our feet also possess several plantar fat pads (under the toes, ball of foot, and heel) that help naturally absorb impact forces, assuming that these pads are positioned properly. In individuals who have worn conventional footwear for years or decades, the forefoot fat pad that’s intended to provide protection for ball of foot structures becomes displaced anteriorly due to a shoe design feature called toe spring. This displacement leaves ball of foot structures (nerves, joint capsules, bones, etc.) vulnerable to the large forces incurred by the body during weight-bearing activity and can cause or make worse conditions such as neuromas, capsulitis, and stress fractures. In those transitioning from conventional footwear to minimalist or minimalist-like footwear, three key pads can be helpful in eliminating discomfort, restoring fat pad position, or augmenting the natural shock absorbing abilities of the plantar fat pads: Pedag metatarsal pads, Strutz foot pads, and Tuli’s heel cups.
Of all the natural protective mechanisms built into our feet, perhaps the most important is the ML arch. Our foot arches, including the ML arch, are natural shock absorbers and are designed, like arch bridges, to bear an incredible amount of weight and force (Note: Many of the bones in the foot are themselves arch-shaped, suggesting that these bones are perfectly designed for bearing weight). In fact, our foot arches are at their best when they are loaded, as this causes all arch components—bones, ligaments, tendons, and other tissues—to mesh to a greater degree. But in order to help stabilize the foot and ankle and absorb shock, the ML arch needs to be on a level and stable support platform. Most conventional shoes, from fashion shoes to athletic shoes, possess a spongy or springy sole that elevates the heel above the forefoot, which in turn acts to destabilize the main foot arch and reduce its ability to effectively absorb and disperse forces. Shoes with minimal cushioning and a completely flat support platform help manage impact forces and enable natural arch support by strengthening the foot’s arches and creating a situation of optimal stability in the foot and ankle.
Might Some People Benefit From Cushioning?
Some of you reading this article may contend that shoe cushioning is essential for foot comfort. And that may indeed be true, especially for individuals who have experienced some sort of foot trauma. However, it’s likely that most people who rely on conventional shoes with plenty of built-in cushioning for foot comfort have done so for many years, perhaps decades, and that their feet have adapted to the environment in which they've been confined. Jumping immediately from cushioned shoes to shoes with relatively little cushioning is not necessarily the right thing for everyone. In fact, a slow transition period is extremely important. This article discusses possible ways to transition to more minimalist-like shoes in a safe and stepwise manner and is particularly relevant for people who have long worn conventional footwear. Adopting a transitional shoe—a flat-soled, wide toe box shoe that possesses a moderate degree of cushioning—before a true minimalist shoe is one approach that many people have benefitted from.
The intention of this article is to put the role of shoe cushioning into proper perspective and to examine the ultimate value of shoe cushioning as a foot health and injury prevention tool. Hopefully this article has presented a new viewpoint on the utility of shoe cushioning or perhaps confirmed your suspicions about the claims of many shoe manufacturers. In our experience, we have found that shoe cushioning (especially excessive cushioning) is often an impediment to optimal foot health, and that true foot comfort can be achieved, in many cases, by restoring proper foot and toe anatomy through the use of helpful and unobtrusive natural footgear. How comfortable a shoe feels is not in itself a good criterion for predicting long-term foot health or even success with a particular shoe. There are a lot of factors to consider when selecting foot-healthy footwear, including taking the time to transition properly. When it comes to choosing the best footwear to put on your feet, exercising care and good judgment is always the best policy. To learn more about the best footwear options for you and your unique foot needs, consider speaking with a naturally-minded foot health expert.
Appendix: Understanding the Numbers
In conducting online research for this article, I found several references for the duration of ground contact that suggested 300 milliseconds (or 0.3 seconds) for the average runner, all the way down to 0.2 or even slightly less for more elite runners. This number seemed to be about the same for both shod heel strikers and barefoot midfoot strikers.
In trying to determine accurate values for the change in vertical velocity of the foot between the heavily shod and the minimally shod, other factors needed to be considered, including cadence and the distance traveled by the foot per stride. Allegedly, an average runner has a cadence of 160 strides per minute, getting up to 180 for better runners. An estimation of the vertical distance the foot goes up in one stride is 0.35 m to 0.4 m. If you double that distance (going up plus going back down), multiple by 160, and divide by 60 seconds, you can determine that the average speed of the foot during a stride has to be around 2 m/s. The tricky part here is that the foot isn't going at a constant speed; it is paused for a moment at the very top as it transitions from going up to coming back down. It’s paused again while in contact with the ground. The simple way to estimate the top speed of the foot is to just double that number, so say 4 m/s on the way down right before impact, and 4 m/s on the way up right after losing contact with the ground. That would give a change in velocity of 8 m/s. Those numbers are based on runners wearing cushioned shoes, so it seems accurate enough to use a value of 6 m/s for minimally shod or barefoot runners.
A very special thank you to physics instructor Peter Peterson and senior mechatronics engineering student Dan Casciato for their kind assistance with various aspects of this article, especially the physics section.