Monthly Archives: November 2014

Biomechanic Issues

Running “correctly” will mean different things for different people—up to a point.

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Next time you go see a marathon, go look at the elite runners—and then look at everyone else.

You’ll see that elite runners run like little toy soldiers: although they have different body types, their running forms are all nearly identical. The further back you get in the pack, the more “variety” of running strides you’ll see. In other words, across all humans, there is a specific recipe for speed.

Our bodies are all different. Some of us have big feet and short calves, others have long calves and really short arms. When a runner has really long legs but small feet, it becomes really easy for the knee joint to open and close: even though the feet are far away from the hinge (the knee joint), it doesn’t take a lot of power to move them because they don’t weigh very much.

In comparison, a runner with short legs and big feet might use the same amount of energy to open and close their knees. This short-legged runner is at a disadvantage, however: shorter legs means that they cover less ground with each gait cycle, meaning that more energy is expended across the same distance.

However, these differences don’t mean that different runners should use different stride types or different body positions. Achieving a “correct” stride will mean that for one runner, the parts of their body will be at certain angles relative to each other, while for another runner, those angles will be slightly different.

But our bodies all express strength in the same way.

For example, let’s suppose that somebody has a really short abdomen but a really long chest. This person may be inclined to hunch down to lift a heavy object, instead of bending their knees. For them, it may be simpler to stretch and contract the longest part of their upper body, their chest, instead of bending their knees, which is what they should do, mechanically speaking. In other words, this person has to work much harder to develop the muscles that hold their lower spine rigid (back extensors, illiopsoas), in order to safely be able to perform this maneuver. But despite these differences, the only mechanically feasible way to lift heavy objects is by bending from the knees.

Similarly, there is only one mechanically feasible way to run: by forming a smooth, unbroken arch from the base of the head to the ankle of the leg that’s pushing off the ground. This arch can only be formed when there is a very pronounced knee drive with the opposite leg (which means that the knee continues to be fully flexed at the end of the swing phase).

Because of individual differences such as those mentioned above, certain runners will have to work a lot harder than others at developing certain muscles, in order to create this continuous arch.

In my case, I have short legs, a short lateral arch (of the foot), and a long medial arch. Without going into the nitty-gritty details, this means that it is very easy for my foot to supinate too early in the running stride. Note that this does not mean that I am “a supinator”—or whatever. This means that my anterior compartment (hip abductors and hip flexors) has to be significantly more powerful than if I had longer legs and shorter feet, in order to maintain a midfoot strike while still using the entire foot tripod for pushoff.

My body has to work harder to keep my foot “more” pronated, and my leg “more” everted, throughout the  running stride, because the muscles that cause my foot to supinate are longer (and therefore get powerful more easily) than the muscles that cause my foot to pronate.

This means that the “untrained” version of my body (without a strong anterior compartment) wants to overstride. Why? Because in order to push off with the entire foot tripod, my body wants to start the contact phase when my foot is at its most pronated. In other words, because I supinate early, my body wants my foot to contact the ground early—and the easiest way to do that is by overstriding.

Furthermore, the only way for that untrained version of my body to midfoot-strike is by contracting the soleus muscle early in the contact phase. In order to go from the contact phase to the stance phase, my ankle has to dorsiflex. But because the soleus was already contracted, it has to work eccentrically in order to allow for this dorsiflexion. This form of midfoot striking put a huge eccentric load on the soleus, which means that my calves can get really really tight really fast if I don’t work heavily on strengthening my anterior compartment.

When I first started running for real, that’s exactly how the story went. My calves were chronically tight, and the answer to that was in developing my frontal compartment. Although different people may have to develop slightly different muscles (for example, someone may need a quadriceps muscle whose lateral head is relatively more powerful than the medial head), the answer for basically everyone who overstrides, or has posterior muscle tightness, is to strengthen the frontal compartment in some fashion.

My end goal was to create a particular structure—a structure which can hold a lot of tensile force, which is firm yet mobile, and which is correctly aligned relative to the force of gravity. As I mentioned above, that structure is a smooth, continuous arch from the base of the head to the ankle. Going about the process of creating that means something slightly different for me than it does for anybody else on the planet.

But nobody will be the most resilient (or fastest) version of themselves without first creating that arch.

Training Ideas

A few ideas for generalized injury-prevention for runners.

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As I often discuss here, I don’t believe that injury-prevention should be put in a different category from athletic training. Injury-prevention isn’t something you should do on the side. It should form an integral part of your training. Why? Because injury-prevention is all about resilience, and as far as the human body is concerned, resilience means using more muscles to achieve the same task.

It doesn’t matter what athletic discipline you practice: running, golf, or martial arts. The more of your body that goes into whatever movement you’re doing, the better off you’ll be. And that means one thing above all others: use more muscles.

That’s why a lot of injury-prevention websites for runner’s knee focus towards working the small muscles—gluteus medius, hip adductors, foot dorsiflexors—a.k.a. all the neglected ones. By putting all of these muscles in play during athletic activity, the body not only becomes more resilient, but more powerful.

In other words, the more resilient you can make your body, the more powerful it will be.

So how can we apply this to running?

One of the main problems most runners experience is that the posterior muscles (calves, hamstrings, glutes, back extensors) become too developed, since they have the most vital functions in the running stride: the first is concentric—extending the leg and back to push against the ground. The second is eccentric—arresting the body’s forward lean so that the runner doesn’t crumple forwards. With a few exceptions, the anterior (frontal) muscles main function is to work opposite to the posterior muscles, in order to allow the runner to lift the leg forwards during the swing phase.

(Think of it this way: muscles at the back generally move body parts backwards, and muscles at the front generally move them forwards).

This means that the most common form of muscle imbalances, which often lead to lateral knee pain and other ailments, are rooted in a dominance of the posterior muscles over the anterior muscles. The most basic thing that any athlete can do, for the purpose of preventing injury—and making their running stride more powerful as a side-effect—is to develop the anterior muscles so that they can move more powerfully.

Given all of this, injury-prone athletes should focus on exercises that strengthen the anterior muscles:

  • Sit-ups that emphasize balance through core activity (such as those shown in this video).
  • Because the gluteus maximus—the most powerful posterior muscle—works not only to extend the thigh but to abduct it (rolling it away from the body), it’s necessary to work on the adductors (which roll the hip in), in order to balance out these muscle groups. Leg/Knee raises help address this. The closer you bring the legs towards the chest, the more you will emphasize the inner abdominal muscles (such as the illiopsoas), as well as the hip adductors.
  • Hanging leg lifts. Doing it with straight legs works the obliques of the core and thigh.
  • Bicycle crunches are also amazing for balancing all of the core/hip muscles.
  • This exercise is great for strengthening to frontal calf muscles.

Even though running is all about triple extension (of the hip, knee, and ankle), you need to be able to flex those joints, in order for your extension to have a greater and greater range of motion. The stronger your posterior muscles get, the more you’ll find yourself “staving off” muscle pain by stretching. The ultimate answer is to strengthen the anterior muscles, so that they can interact properly with the posterior muscles.

For a sport like running, you can count on the posterior muscles to take care of themselves. It’s the anterior muscles (and obliques) that you have to worry about. I love this quote by The Gait Guys, which captures all of this in one simple thought:

“Develop anterior strength to achieve posterior length.”

Thinking in Systems

The human body is an athletic machine.

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A growing body of evidence is telling us that exercise is one of the most important ways to prevent all sorts of chronic diseases. This list includes (but is not limited to) various cancers, diabetes, clinical depression, and osteoporosis.

Although we could just leave it at that, and say “exercise if you’re chronically ill,” we can take this evidence a little bit further: it tells us something very important about the relationship between exercise and the human body.

What chronic diseases mean for the body is that our systems aren’t resilient: the very same problem springs up again and again, and our body has los the capacity to change that. Because by exercising, we can reduce the risk for these diseases, this tells us something about the optimum state of the body: when we don’t exercise, our risk of chronic disease begins climbing. When we don’t exercise, our bodies stop being resilient. This means that the body’s resilient state is one in which it’s constantly exercising.

There is another growing body of evidence that suggests that cognitive flexibility and neurogenesis (the creation of neurons and neural pathways) increases during exercise. This means that, both physiologically and psychologically, exercise increases the body’s capacity to deal with new, novel, and unexpected stresses. Simply stated, exercise helps the brain and the body meet the demands of the world on the world’s own terms.

Thanks to this evidence, we can infer something about the body: if the human body and human mind’s resilient state corresponds to a state of constant activity and exercise, then the body isn’t meant to be passive, at rest, and unchallenged. The human body’s baseline state is one of exercise—one where it’s being constantly challenged physically, physiologically, and mentally.

In other words, the human body is an athletic machine.

This conclusion tells us something very interesting: the prototypical western, sedentary human doesn’t reflect the optimum state of the human body. And to snuff out a possible counterargument before it arises: we haven’t “evolved” out of the athletic roots that were so important in our early history and prehistory. Socially, we may be an entirely different animal (although many, myself included, would argue against that—we are as reactive, addictive, violent, aloof, and oppressive as ever). But physiologically and psychologically, we’re basically the same. If we had in fact evolved beyond those athletic roots, exercise would have no causal relationship whatsoever to chronic disease.

Which in turn opens up a very interesting line of inquiry: the pool of subjects used when we move new cures and treatment methods into human testing is highly skewed: we test these methods and cures on a population that, while ostensibly representative of the western, sedentary human, is not representative of the ideal—i.e. resilient—state of the human biological and psychological system.

What this basically does—and has done—is to get us into a mindset where prevention doesn’t exist, and cure is the only option. In systemic terms, prevention means increasing the resiliency of the system. Once that system is resilient beyond a certain threshold, there still may be some ailments that need curing. But when the prospect of increasing resilience is completely off the table—or worse, marketed as an “alternative,” and not as the necessary first step towards a solution—everything needs curing.

Biomechanic Issues

On the importance of the Internal Obliques.

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I just read a very interesting article on the importance of the internal obliques for the walking and running gait. Here’s a tidbit:

If you don’t own your obliques, you don’t own walking. If you don’t own walking, you don’t own movement. If you don’t own movement, you don’t own your spine. It’s that simple.

When the gluteus maximus (butt) muscle isn’t working well, the internal obliques sometimes take over the task of extending the hip. This compensation pattern can devolve into a series of other musculoskeletal problems. The article makes some key observations:

  • Since the internal obliques (quadratus lumborum) control the deceleration of the spine’s rotation, they are instrumental in maintaining spine stability and avoiding injury.
  • One of the hallmarks of oblique weakness is that people stop breathing when performing simple movement patterns to maintain stability. (This makes it essential for runners to focus on oblique function; incorrect breathing patterns and/or an inability to change them may be rooted in oblique weakness).
  • Because spine rotation is essential for gait, improperly-functioning obliques will impair the production and absorption of mechanical energy.

It’s always important to remember that a particular dysfunction has repercussions all over. Oblique functioning isn’t just about spine stability or just about breathing, or just about production and absorption of energy. A dysfunction in any one system has repercussions on many levels in a dynamic system like the body.

Biomechanic Issues, Thinking in Systems

The “heel-striking” running gait doesn’t observe the requirements of the human body’s mechanical paradigm.

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Those who say that the midfoot strike is the “ideal” running stride often conclude that midfoot striking is “better” for a variety of reasons. One of those reasons is that, allegedly, the midfoot strike is more “natural” than the rearfoot-strike (also known as the heel-strike).

It’s a bad idea to call the midfoot strike more “natural”—aside from the fact that the allegation is wrong: humans use a variety of different footstrikes for a variety of different activities. Rearfoot striking ahead of the center of gravity is the default walking strike. Rearfoot striking is also used to abruptly halt forwards momentum, and sometimes, to turn by using the heel bone as a pivot. Conversely humans use a very anterior (forefoot) strike during the acceleration phase of sprinting.

In short, the problem with this “natural” argument is that human feet strike the ground all over the foot map.

So stop calling it natural.

Which is why I prefer to adopt a more technical term: paradigmatic function. This term means that a certain function X is more in line with a particular structure, or a particular configuration of a structure.

For example, variable-geometry aircraft—those which have the ability to “sweep” the wings back from an extended position to create a triangular shape (such as the F-14 Tomcat)—use the swept-back configuration for combat and supersonic flight, while they use the extended (regular) position for takeoff and landing. For the F-14 Tomcat, the paradigmatic function of the extended configuration is takeoff and landing, whereas the paradigmatic function of the swept-back configuration is combat and supersonic flight.

tomcat

Although it is no doubt possible for the F-14 to land with the wings swept back and enter combat with the wings extended, there are two things to consider: (1) each configuration works better for each activity, meaning that (2) each configuration “solves” a different problem: the swept-back configuration allows for greater maneuverability and speed, while the extended configuration allows for greater stability and reduced speed during landing.

Central to systems thinking is the idea that every system (or configuration of a system) is built to solve a particular problem. For example, a system with a branching structure, like a tree, a lung, or a network of roads, solves the problem of getting the maximum amount of energy or nutrients to and from various places with the least amount of effort. The shapes of systems always correspond to the most parsimonious way to solve a particular problem. In a very real way, you can think of all systems—and each individual configuration of those systems—as solving a problem that is specific to each system or configuration.

The very same goes for walking and running, the two important gaits—the two functional configurations—of the human body.

Although it would seem easy to say that these two functional configurations are “walking” and “running,” it’s better to get at this conclusion in a more roundabout way:

In terms of the stresses absorbed by the body, the most important difference between walking and running is that in running, there is a flight phase, while in walking, there isn’t. This means that one of the things that the body needs to do while running is absorb the shock of landing, while in walking, this particular need is largely absent.

This theory is largely borne out by looking at the muscles used during walking: the largest muscles in the body—the gluteus maximus, the psoas major, and the hamstrings—are largely inactive.

Because of this, the knees remain locked during the walking gait. This means that by walking, the body “solves” the problem of preserving energy while remaining in motion; that’s what the walking configuration is for.

Because a necessary component of running gait is the absorption of shock, the landing portion of the running stride should incorporate a shock-absorbing motion. So, in order to figure out what kind of motion comprises the landing portion of the running stride, let’s review what a “purely” shock absorbing motion looks like: landing from a jump.

When we land from a jump, our hip and leg mechanism works largely like a shock-absorber: we land on our midfoot or our forefoot, and all the joints of the lower extremity go from a lot of extension to a lot of flexion in less then a second, meaning that the hip, knee, and ankle all flex together. (This is known as triple flexion). This means that the paradigmatic function that the body uses to absorb shock is triple flexion. Similarly, in order to jump again, the body extends the hip, the knee, and the ankle simultaneously (which is known as triple extension).

Exchanges_Triple-Flex-Ext

In order to create triple flexion and triple extension, the body must recruit the largest muscles of the body, including the hamstrings, gluteus maximus, psoas major, and quadriceps. In other words, the triple flexion/extension configuration solves a very different problem than the one solved by walking: it allows the body to safely absorb the energy of impact, while powerfully exerting force against the ground.

Because running necessarily has a shock-absorption component and a takeoff component (because of flight time), it stands to reason that, during running, triple flexion and triple extension should form an integral component of the contact and pushoff phases (respectively).

This is where it gets problematic. The typical heel-strike (overstriding with initial rearfoot contact) plays out very differently from triple flexion: as the foot strikes the ground, the knee is mostly locked but the leg is stretched out in front and the foot is raised. The hip is in flexion, the knee in extension, and the ankle in flexion. This means that the shock absorption capabilities of the leg are reduced—and because the leg flexes less, it has a lower capacity for pushoff.

heel-striking

(The lower achilles tendon loading of heel striking as compared to forefoot striking may attest to this).

I’ll leave the issue of heel-striking under the center of gravity for another post. For a taste of why it might be problematic, try jumping up and down in the same spot while landing on your heels. It’s extremely difficult.

In contrast, the midfoot/forefoot strike is a great example of the triple flexion/triple extension principle at work: When you land on your midfoot, your leg compresses like an accordion: the ankle, knee, and hip create a zig-zag shape, which straightens as you push off. Midfoot striking adheres strongly to the musculoskeletal configuration used for shock absorption/propulsion movements.

forefoot-striking

In my opinion, the best way to know if you “are” a heel-striker in some essential sort of way is to jump up and down, and to see if it is easier for you to absorb shock by landing on your heels than by landing on your midfoot or forefoot. (Unlikely). If that isn’t the case, and yet you heel-strike while running, it might be time to look at muscular imbalances and power leaks, particularly in regards to muscular interactions at the hip area (illiopsoas, lower back extensors, gluteus maximus, quadriceps, and hamstring).

And then, embark on the long road of responsibly changing your gait.

Biomechanic Issues, Defining our Terms

A question of systemic resilience: is it more “efficient” to run shod than barefoot?

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The idea that running barefoot offers a metabolic advantage over running shod may be an “appeal to nature” fallacy.

Although some studies have found that running barefoot is actually “more efficient,” there have been a host of other studies that contradict those results.

So we can’t say for sure.

In a 2012 study titled Metabolic Cost of Running Barefoot Versus Shod: Is Lighter Better?, Franz et. al. set out to debunk the claim that barefoot is indeed more efficient. In a nutshell, their results found that not only did barefoot running have no metabolic advantage over running shod, but actually seemed to be more metabolically costly to do so. It has been suggested by several studies that the reason for this added metabolic cost is because of a “cost of cushioning.” According to these studies, the body is making an effort to absorb impact when running barefoot, that it doesn’t make when shod (more on this later).

I largely agree with the research question, experimental design, and results of Franz et. al. But reading this article stirred up several theoretical issues that don’t have much to do with the article in particular, but are important in terms of how the shod/unshod and hindfoot/forefoot striking debates have unfolded, particularly regarding what the terms “efficiency” and “better”—as in the title of the study mentioned above—have come to mean in this debate.

Franz et. al. begin the article by writing that “advocates of barefoot running claim that [barefoot running] is more “efficient” than running in shoes.”

First I’ll address the question of what we mean when we say “efficiency.”

It’s important to be clear that the advocates that Franz et. al. cite (Richards & Hollowell, authors of The Complete Idiot’s Guide to Barefoot Running and Sandler & Lee, authors of Barefoot Running) are using the classical definition of “efficiency” as do Franz et. al.—meaning that they claim there is a lower energetic cost to barefoot running. That claim may well be a fallacy, and Franz et. al. are right to debunk it.

But I want to draw attention to a different use of “efficiency,” which will eventually get us to analyze what we mean when we say that one function (say, shod running) is better than another (say, barefoot running). In order to do this I need to bring in one of my favorite concepts from systems thinking: resilience.

One of the hallmarks of a resilient system is that it is built out of many tightly-coupled feedback loops, which basically mean that there is a lot of movement and interaction between its various parts. And for that movement to exist, the resilient system must be spending larger quantities of energy than the less-resilient system.

(This idea is rooted in thermodynamics: the movement of molecules and atoms correspond to the amount of energy stored in a certain space, i.e. the temperature of that space). The idea that greater movement can only be produced by a greater use of energy is generalizable to basically everything.

Note, however, that the causal relationship between resiliency and increased consumption of energy only goes one way: all other things being equal, a more resilient system must be using more energy than a less resilient one, but a system that uses more energy than another is not necessarily more resilient.

In the classical definition of “efficiency” that Franz et. al. and the barefoot running advocates are using, the resilient system is less efficient—i.e. it is at a metabolic disadvantage, since it uses more energy—than the non-resilient system. It isn’t very useful to speak in terms of “efficiency” when we’re talking about complex behaviors like athletic performance: for example, when the body finds itself in crisis, it will begin shutting down major organs to conserve energy. And for every organ that it shuts down, the less resilient it is: it becomes less and less able to cope with new and unexpected crises. Is this more “efficient” in any reasonable sense of the word but the classical? Not really.

“Efficiency” in the classical sense has never been the goal of human running. In Waterlogged, Tim Noakes explains how running on two legs has a much greater metabolic cost, across the same distance, than running on four legs, and yet, because humans run on two legs, we are capable of running down antelope and other ungulates in the desert. (The advantages that running on two legs offers are thermodynamic, but that’s a story for another time).

Simply stated, if efficiency was what the human body wanted in the first place, we would have never gotten off all fours. Actually, we would never have become runners at all. But we did. So there has to be more to this story. By standing on two feet, there has to be another problem that we were trying to solve beyond “efficiency.” That problem is most likely how to be resilient in the performance of particular function: human endurance running.

The human body—like any system—has other goals beyond pure efficiency. Indeed, one of the primary goals of the human body is redundancy. Studies have shown that even when we exercise at maximal intensity, only a fraction of our sum total muscle fibers are recruited. In the classical sense of “efficiency,” you could say that it is less efficient to be redundant, since more energy and nutrients must be spent building these redundancies instead of using them for athletic performance.

All of this gets us to what we mean when we say “better.” In a very real way, (and for a variety of reasons), it isn’t “better” for the human body to be “more efficient” in the classical sense. It’s better for the body to be more redundant, and more resilient. In theoretical systemic terms, the fact that the number of active “feedback loops” increase when  running barefoot—since the touch receptors on the soles of our feet “feed back” information to our muscular system, which works to decrease impact—is indicative of the likelihood that the unshod system is more resilient than the shod system.

touch rec m

Furthermore, when we blow up the term “efficiency” onto the large scale (divorcing it from its classical meaning), we can ask ourselves: in time and energy, what are the advantages of protecting the system, over not doing so? According to the literature, wearing shoes doesn’t protect the system in its entirety, beyond the skin on the sole of the foot: It has been shown consistently that shoe cushioning doesn’t affect peak impact force, only our perception of that impact. Peak impact force is alleged to be the main cause of repetitive stress injury in runners. While it has also been shown that in hindfoot-striking, shoe cushioning decreases loading on tissues), loading is a very different issue, with different consequences to injury, than impact.

Given that running shod reduces the activity of our cushioning mechanism, it would be extremely informative to do a long-term study on the amount of impact absorbed by the tissue (as opposed to loading), when the cushioning mechanism is deactivated. (Short-term studies already provide evidence that impact forces are indeed reduced when running barefoot as opposed to running shod). In turn, it should be explored how the increased impact translates to tissue damage, recovery time, and ultimately time not spent developing athletically.

In these terms, we may yet discover that it is more “efficient” for the body to run barefoot than shod. Being this the case, we could say that it is “better” for the system to run barefoot than shod.

Whether this is actually the case remains to be seen. What we can do at this point is to observe how our words shape our perception, attention, and inquiry, and what it is that systemic insights can bring to the table, both theoretically and with an eye towards future experimental research.

Biomechanic Issues

A functional argument in favor of midfoot striking: putting the research in context.

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The human body is a machine with particular characteristics. So is a car. Just like the many different makes and models of cars have slightly different capabilities, human bodies are all different.

But they are not that different. For example, the operational requirements for all cars are very similar: the centrifugal force generated during a turn must not exceed the friction generated by the tires. And they are the same in humans.

But that’s not the way in which much of the medical and sports science literature treats it. Don’t get me wrong: everybody is in agreement on what the individual parts do: the gluteus maximus abducts and extends the hip; the gastrocnemius points the foot, etc. But there is a vast amount of disagreement as to how these parts are supposed to work together. Rather, there seems to be quite a bit of agreement that for the same systemic function (running), the individual parts can be performing wildly varying functions, and yet the system will still be somehow performing correctly.

I am, of course, talking about the footstrike debate. Before I continue, let me be clear that by “heel-striking” I don’t refer to how the foot hits the ground. I refer to the set of gait characteristics that contribute to overstriding by reaching forwards with the leg and striking the ground heel-first. The same goes with the gait characteristics associated with midfoot striking.

I’ve been reading a series of articles that associate different patterns of loading with different stride types. For example, a heel-strike is typically associated with increased loading of the knee, while a forefoot or midfoot strike is typically associated with an increased loading of the ankle and achilles tendon.

Most of the articles that I’ve read tend to conclude that therefore, we should see greater knee injury rates for heel-strikers, and greater achilles injury rates for forefoot/midfoot strikers.

However, that’s a hypothesis. By this I mean that thus far I’ve found no studies that have shown that these hypothesized injury rates actually occur.

The question is this: are all tissues equally amenable to loading? In principle, absolutely not. Buildings often have central support structures to carry the load. So does the body. The question is whether, say, the presence of the achilles tendon—a dense, springy structure capable of storing massive amounts of potential energy (also the largest tendon in the body)—makes the ankle more amenable to loading than the knee.

In principle, it makes sense that the presence of the achilles allows the ankle to be loaded more than the knee. However, this remains to be ascertained by future studies.

For now, what we can say is that the differences in loading associated with one foot-strike pattern aren’t “equal” to another. Because certain structures are paradigmatically employed by the body to support weight, absorb shock, and store potential energy, a foot-strike pattern that offsets loading to these structures will, in general, be more amenable to the overall health and functional performance of the body. Whether experimental research ascertains that the achilles tendon is such a structure remains to be seen.

However, I certainly agree with the general supposition that a stride type that places more emphasis on loading of the achilles tendon (such as midfoot striking) generates a higher incidence of injury for that structure. Across a population, use of a particular structure will almost necessarily correspond to an increase in injury and overuse rates of that structure.

It remains to be experimentally ascertained whether a stride type which offsets loading onto dynamic structures (muscles) and energy storage structures (tendons and fascia), will, across a population of individuals, create lower overall injury rates despite the likely increase in injury rates due to simple use of those structures.

However, we can still make a systemic analysis.

Let’s use the example of an airplane as an analogy: it is much more efficient for an airplane to use flaps, than to not use them. By increasing the total wing surface, flaps allow landing and takeoff velocity to decrease by a significant amount. An increased use of flaps will no doubt mean that, overall, more flaps will become damaged and broken than if flaps weren’t used at all. But because flaps help reduce the speed at which the aircraft lands, using them contributes to a decrease overall structural stress and damage associated with the impact of landing.

You could even make the argument against using flaps by saying that increasing the wing’s surface area will put more stress on the wing housing and the airplane’s airframe. Even though this is the case, making this argument misses the point. The point of the airframe—and especially of the wing structure—is to absorb the increased stresses associated with increasing the wing surface. Flaps should be used during landing regardless of the fact that both stresses to the wing and incidences of damage to the flaps will increase.

Along similar lines, if we posit that a certain body structure has a certain function, such as the achilles as a structure to store mechanical energy, the gluteus maximus as the main driver of hip extension, etc., then, under optimal conditions, the body should preferentially load the achilles upon landing and put the burden of moving the leg on the gluteus maximus. (All of which seems to agree with the findings of this study):

“When compared to RFS (rearfoot strike) running, FFS (forefoot strike) and BF (barefoot) running conditions both resulted in reduction of total lower extremity (leg) power absorption particularly at the knee and a shift in power absorption from the knee to the ankle.”

All of this said, the systemic analysis of the body is simple: in systems thinking, you look at the functions of different parts, in relation to the whole, to ascertain their function. The achilles tendon seems to be primarily a shock absorber. It certainly works that way when jumping—that’s why it’s almost impossible to land on your heels when you’re jumping straight up and down. So, any stride type that uses the achilles tendon as a shock absorber will likely be more amenable to the body.

Until evidence otherwise settles the matter—and only until then—the most reasonable conclusion to make is that a stride type that uses load-bearing structures to carry weight, offsets torque (rotational force) to joints that can rotate dynamically, uses shock-absorbing structures to absorb shock, and employs energy-return structures to return energy, are “better” than stride types that do not. Given the evidence currently in the literature, everything seems to point to (but not prove) the idea that midfoot striking is an example of the former, and heel-striking is an example of the latter.

AN IMPORTANT CAVEAT: The body is a dynamic system, which means that you can think of it this way this way: if you change one thing, such at the angle at which your foot touches the ground, three other things will change along with it. Perhaps you’ll see a change in your forward lean, a change in your hip extension moment, and therefore a change in the loading of a variety of muscles. In other words, you can never change only one thing. If you oversimplify your understanding or implementation of the changes you need to make in order to be faster, more efficient, or less prone to injury, you will end up being slower, less efficient, and more prone to injury.

This is why it’s important to talk about forefoot striking, midfoot striking and heel striking as “types of gait” and not as “types of footstrike:” the angle at which the foot hits influences (and is influenced by) a variety of other factors. My contention (which I believe is also the contention of proponents of midfoot striking) is that for a supermajority of people, the resolution of all of the biomechanic factors surrounding injury, muscle imbalance, power leaks, and resolvable musculoskeletal asymmetries, will result in the adoption of a midfoot/forefoot strike.

Again, whether this is actually the case has not been borne out by research.

I’d love to read what you have to say about this. Please put your comments, criticisms, and questions in the comments.

Biomechanic Issues, Thinking in Systems

An analysis of the paradigmatic features of midfoot-striking and heel-striking.

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The term “heel-striking” shouldn’t just refer to which part of the foot hits the ground first. Even in the common parlance, it should refer to the collection of neuromuscular gait features across the body that contribute to a type of overstriding in which the heel lands first, ahead of the center of gravity.

When I write the words “heel-striking,” this is invariably what I mean.

This way, we can neatly sidestep the conversation of whether someone landed on their heel under their center of gravity, or only “appears” to heel-strike. Let’s do away with reductionist analyses: let’s make it about something else than just “the strike.” The most widespread way in which the western runner overstrides is by heel-striking.

In a previous post, I reviewed how there is a paradigmatic body geometry to midfoot-striking, which corresponds to a paradigmatic pattern of muscle use. Heel-striking is no different.

When I say “paradigmatic,” I refer to the core components of the stride; to its most generalizable features. For example, the paradigmatic body geometry of midfoot-striking consists of a full-body arch, which begins at the base of the head and ends at the heel.

Establishing the paradigmatic features of types of running strides allows us to observe those features and make reasonable predictions about them. If you look at a runner who appears to be heel-striking, and yet is creating a full-body arch starting from the base of the head and ending at the pushoff heel, you can be reasonably certain that if you look closer, you will actually find this runner to be midfoot-striking. In other words, you can know that Meb Keflezighi’s apparent heel-strike (left), is actually a “proprioceptive heel-strike”—rather, a “disguised” midfoot-strike—just by looking at the continuous arch made by his leg and back at pushoff. (This video makes my point rather well). You may notice that other noted forefoot-strikers create very similar arches:

elite arches m

Because every person has a slightly different body geometry, the specifics of their stride will be slightly different. But these specifics are much more similar to each other than it is usually claimed. For example, in the post previously mentioned I reviewed how, necessarily, for all humans, dynamic strength is necessarily achieved by creating a series of consistent and symmetrical arches with the body’s bone structure. The reason this applies to all humans is because it applies to all structures. The integrity of every possible structure—from the Hagia Sophia to the plantar vault—is subject to the symmetry and consistency of its arches.

From this idea, we can extrapolate that no human can be the strongest version of themselves without creating the most consistent and symmetric arches across the body. Therefore, when you look at the differences betwen midfoot-striking and heel-striking, the differences in body geometry stand out starkly: unlike midfoot-striking, heel-striking paradigmatically breaks the full-body arch that makes the midfoot-striking body so resilient.

There may be a few runners out there for whom a true heel-strike doesn’t break this full-body arch. There may even be others who can land on their heels, under the center of gravity, without breaking this arch. But paradigmatically, the stride difference between forefoot-strikers (left) and heel-strikers (right) looks like this:

heelforefoot1

As mentioned before, a paradigmatic body geometry corresponds to a particular pattern of muscle use. In the above graphic, you can observe major differences between midfoot-striking and heel-striking in the neuromuscular paradigm of both the extensor muscles used during pushoff (red) and the flexor muscles used during the swing phase (blue). Of course these two types of body geometry load different tissues in different ways. That’s the point.

The most important differences are (1) the reduced iliopsoas function for the heel-striker (depicted by a grayed out X at the hip), (2) the reduced function of the upper back extensors (grayed-out X at the back), and the concentric activation of the quadriceps muscle for the heel-striker (blue arrow at the thigh).

The heel-strikers’s upper leg is in a bit of a predicament: during the swing phase, both the quadriceps (front thigh muscle, blue), and the hamstring (back thigh muscle, blue) are active at the same time. This is a problem because, when the leg is forwards of the hip, the hamstring flexes the knee, while the quadriceps extends it. This means that two muscles of the body which perform opposite functions are active at the same time, pulling in opposite directions. And this is happening as the leg is nearing the ground—during the landing phase—which means that two of the major muscles of the body are fighting each other, and they are doing so at the very moment that the body is about to slam into the ground.

This isn’t a problem for the midfoot-striker: the fact that the front knee is bent, and near the height of the hips, means that the quadriceps is largely inactive at that stage. Full quadriceps activation only occurs towards the end of the pushoff phase (front thigh muscle, red).

Because athletic power is generated through the creation of consistent and symmetric arches, any running body will always be the most powerful version of itself as a midfoot-striker. Furthermore, the body is designed around these principles: because load-bearing structure (the arch) is most consistent when the body is powerfully midfoot-striking, the body is at the peak of structural resilience when midfoot striking. Given that resilience is a hallmark of systemic integrity, this means that a systemic analysis of the body can only basically conclude that the human biomechanical system is operating at its “peak” when it is midfoot striking.

Similarly to the heel-strike, the midfoot-strike doesn’t refer to the part of the foot that hits the ground first. It refers to the constellation of stride components (such as the creation of a full body arch), that allows this part of the foot to hit the ground first.

This post shouldn’t be construed to mean that we should ONLY midfoot-strike. There may be plenty of reasons to heel-strike, such as rapid deceleration, and the opportunity to use the heel bone as a swivel, in order to turn quickly. However, for the purpose of producing safe and sustained forward motion, no type of stride will yield results that are as consistent or as powerful as those allowed by the midfoot-strike.