Tag Archives: running economy

Synthetic perspectives on the running human body: Improving running economy is not the be-all, end-all.

Looking at the body from a synthetic perspective is a lot like looking at it from an evolutionary perspective.

As I described in a previous post, a “synthetic account” of the body—there is no such thing as a “synthetic analysis”—is one that looks at the human animal in its whole context in order to understand why it does what it does, (and what it is attempting to do).

A few theories have a strong synthetic component: Pose Method (which looks at the mechanics of the body in the context of the Earth’s gravitational field), Tim Noakes’ Central Governor Theory as well as his discussion on thirst and hydration, and Phil Maffetone’s MAF Method (which observes that prolonged athletic achievement cannot be produced without safeguarding and promoting the body’s health).

But most accounts of athletic performance out there look at the human body in a very narrow analytic sense. They typically only measure a few variables germane to athletic performance: running economy (also known as efficiency), speed, power, endurance, etc. In other words, they look at the body in the same way you might look at a race car: you analyze how the race car functions and how it performs while on the track. But you don’t worry very much about what it’s doing or what’s happening to it elsewhere.

In this vein, it is often argued that one running form (one particular set of kinematics) is better or more advantageous than another on the grounds that it is more efficient. Take a look at the title of these articles: A Novel Running Mechanic’s Class Changes Kinematics but not Running Economyand Effect of a global alteration of running technique on kinematics and economy. 

The body has to worry about a number of things beyond running economy: it has to save itself for future battles, quickly rest and recover in order to fulfill any number of foreseen and unforeseen functions beyond the scope of the athletic event, like for example to be unstressed enough to be able to engage smoothly and creatively with social environments.

So, when sports scientists come along and suggest that the best form for a particular athletic movement is what’s most efficient (in the sense of minimizing energy expenditure during the athletic event), they are ignoring some of the body’s broader imperatives.

Why? The simple answer is that the body’s lifelong goal of protecting itself is far more important to it than the very bounded goal of winning some particular athletic event (or chasing down some particular deer) at any cost. It doesn’t just want to get the deer. It wants to benefit from having gotten it.

What does this mean? That benefiting from getting a deer means that it might be better to wait until a slower deer comes by. Let’s suppose you don’t have enough energy to run at the speed and distance you’ll need if you want to catch the deer you want, and still be able to run with the form necessary to protect your body while doing so. You might end up catching the deer, but you might also end up with a blown knee or a damaged achilles. You might be put out of commission for a month or two.

Now let’s suppose that someone else uses a slightly more expensive form—expending more energy to maintain proper movement. They’ll be proportionally slower, but they’ll also be able to move much more and recover much faster. Over time, they’ll become the more powerful runners. Three or four years down the line, they’ll be catching much faster deer, much more consistently.

Of course, it’s important to be as efficient as possible: refining the way muscles work, and aligning them to work with gravity and impact forces (and not against them). But pursuing efficiency is not at all convenient past the point where the only way to get more efficient is to risk tearing tendons, degrading cartilage and connective tissue, and abrading bone.

This brings up another important point: while the safest form has a high degree of efficiency, the checks and balances necessary to produce it (and maintain it at high speeds or over many miles) also means that it is typically more expensive to produce than the “most efficient” form.

 Let’s say that the runner who blew his knee by going after the very fast deer has form X. Form Y might be more expensive, but it would also allow him to get faster over time. But let’s say that instead of getting injured by going faster, he decides to only chase the slowest deer, or run exclusively for fun. He might display the same injury rates as runner Y. But if we only look at injury rates without looking at speed, or running economy without looking at speed, or efficiency without looking at performance improvement over time, we might end up concluding that the wrong ways of doing things are actually better (or worse, that there is no “best” way of doing something).

Being faster (or fast for longer) is great. But that’s not good enough either. The same things that we said about efficiency can also be said about speed. Running with the form that lets you be fast safely, recover quickly, and improve consistently, is waaay better than “just running fast.”

Walking, jogging, running, and how gravity defines them.

What is the difference between walking and running? As runners, particularly runners who often stake their identity on running, this is a question that we should have thought deeply about. But the reality is that in the vast majority of cases, it remains ignored.

Say, the simplest and perhaps most important difference between walking and running—or at least the one with the most consequences—is that running includes a flight phase while walking does not. In other word, walking has a static interaction with gravity, while running has a dynamic one. But upon further consideration, there’s a lot more to be said:

Bounding (by which I mean jumping continuously) also has a flight phase. So does skipping. Of course, these are obviously different from running in that running alternates support, similarly to walking, whereas bounding does not (since both feet land together) and neither does skipping (since each foot repeats its support of the body before alternating to the other).

Running is somehow special when you compare it to bounding and jumping, at least as far as the body is concerned: when we need to travel faster than walking allows, neither bounding or skipping are our go-to methods of travel. Instead, we run. Although this may seem too obvious to be important, it’s important precisely because of that: What is it exactly that running offers us?

All the biomechanics junkies are way ahead of me at this point. Running offers us a way to contralaterally (read: using one leg and its opposing arm) maintain balance and support: when one leg pumps down, the other arm comes up, allowing the body to push on the ground alternately while not compromising balance.

And there’s another requirement: running uses the energy return capabilities of our tendon system (in particular the achilles tendon) to maximize running economy. This means that, by loading the achilles tendon like you would load a spring, the body manages to put the force that it arrives at the ground with into the next step, to make running more “economical” by reducing the amount of energy that the body puts into the next stride cycle: the achilles tendon stretches during the landing and stance phase, and then shortens explosively during pushoff, when the leg and foot, well, push off against the ground to begin the next stride cycle.

Neither bounding nor skipping allow us this increase in economy: to be able to bound successfully, we would have to be counterbalanced in the sagittal plane, (read: front to back) in order to put the hips at the midline of the body. Basically, we’d need a tail. But since we don’t, when we land from a bound (or squat), the hips are behind the center of gravity, and the knees are in front, in order to compress the body properly.

But if we had a tail like a kangaroo, the hips would remain under the center of gravity during the landing phase, because our weight would be more evenly distributed behind and forward of our hips. Without going too far into it, this means that the force put into each bound is primarily generated by muscle power for us, whereas for the kangaroo it is a product of tendon energy return. Skipping doesn’t increase economy either since energy is lost in that second step before alternating legs.

Flying-kangaroo

So, we can begin to lay down the differences between running and walking in this short list:

  1. A flight phase
  2. Contralateral stance and equilibrium
  3. A maximization of running economy

This is where we finally get to why “interaction with gravity” is so important: when running, the human body puts itself at risk of injury by taking off and then accelerating back to the ground, but it is counting on using that acceleration, generated by the force of gravity, to power its next step. This means that an important amount of the energy that is being put into each step is borrowed from the last, and doesn’t come from inside the body at all.

Running diverges from jogging in the following way: Jogging doesn’t really harness the energy return properties of the tendon system. It doesn’t allow for an improvement in running economy. Why not?

In order to create energy return, the relevant tendons (say, the achilles) have to remain taut during the landing phase, in order to stretch. This means that as the foot lands, the extensor muscles along the rear of the leg (hamstrings, gastrocnemius, glutes) begin contracting even as the frontal muscles (quads, tibialis anterior) take the majority of the load.

When the back and front muscles play together like that, a large amount of the energy that the body accelerated towards the ground with goes into the tendon system, and gets released as the foot leaves the ground.

During a jog, the leg muscles are working in a fundamentally different way. Because a jog is slower than a run, the forces being generated are a lot smaller, and so a the rear and the front muscles of the leg can work relatively independently of one another: the front muscles take the body’s load when the foot comes down, and the back muscles push off as the leg goes back. The tendons never become stretched, so they don’t get loaded that much at all.

This means that the jogging cadence is much slower than the running cadence: in order to maximize tendon load, the body is forced to increase the speed and rate at which the legs hit the ground: since the muscles at the back of the leg tense the tendon springs, this drives the leg down at a much greater speed than otherwise, resulting in a faster transition from landing to pushoff, resulting in a much faster stride rate.

However, this also separates jogging from actual running from a power standpoint: in order to run rather than jog, the muscles must be powerful enough that they can hold the tendons taut while the weight of the body comes down. (And of course, the tendons must be resistant enough to support this).

This is the minimum bar in order to run—developing enough leg power (and naturally, the aerobic power necessary to sustain it) that three interrelated capabilities emerge:

  1. The ability to hold the tendons taut throughout the stride cycle.
  2. Increasing the stride rate and successfully maintaining it.
  3. Equipping the body to successfully load tendons instead of absorbing power with muscle and bone tissue.

I believe it is these three capabilities that make someone a runner.

Muscle strength and running economy — a “chicken or the egg” problem?

Runners are often told that strength training is integral to improving running speed and running economy. But there might be a little bit of a problem with this advice. I recently posted about a body of research that pointed to the idea that, for a variety of biomechanical reasons, weaker muscles in a trained runner correlated with a greater running economy (specifically at the calf region). The consensus was that running economy increased with achilles tendon loading, and decreased with calf muscle (gastrocnemius and soleus) activity.

More muscle means worse economy. A recent article in Runner’s World confirmed this, citing a study that found that running economy was related to the balance of strength between the anterior and posterior muscles (specifically, the quads and hamstrings). It was not, as most of us suspect, a function of pure muscle strength—overall, competent runners had weaker muscles than novice runners.

This brings up several questions. The first is, of course, how can weaker muscles make you run faster? The answer, I believe, is systemic, and our ability to find it hinges on what we mean by “strength training”—and how usefully we’ve defined it for ourselves. In the most basic terms, the strength of an individual muscle has little to no bearing on how the hip-leg-foot mechanical system will function in practice.

The power of this system—when power refers to how much force the leg can put out per unit of time—is much more a function of how well the parts move together, than how strong any individual part (or indeed, all of its parts) are individually. Someone endowed with extremely strong muscles that are all just slightly out of sync will have a completely rigid leg, not a powerful one.

It’s necessary, therefore, to make sure we all mean the same thing by “strength training.” Strictly speaking, the kind of explosive power (plyometric) training that a lot of runners do, which actually does develop hip and leg power, is “strength training”—but of the entire system. We need to be clear on what we mean by this to know if strength training will actually help us become better runners. Do we mean pure strength, or explosive strength?

The second question is more related to a practical matter, and is a consequence of answering the first. What are our reasons to train pure “muscle strength” in the first place? We’d better have them, given the above evidence that muscle strength correlates with low running economy. If we do prescribe a strength training program to runners, are we potentially hurting their running economy?

I don’t have an answer for this. Most of my training is either isometric or plyometric, and the few strength exercises that I do—such as barbell squats—are for balancing my body out, more than anything.

The third question is a matter of causality: why did the novice runners in the Runner’s World article have stronger muscles? To speculate about this, we have to return to the body of research mentioned above. The reason that weaker muscles correlated with greater running economy has to do with the biomechanics of particular bodies. One of the abovementioned studies looked at the ankle region of highly-trained runners, and found that runners who had longer heels (meaning a greater distance between the ankle and the heel) had poorer running economy and greater muscle power.

None of this is surprising, once you think about it. When the hip-leg-foot system pushes against the ground, it exerts force directly into the ground, at a perpendicular angle. To achieve this, the foot works a lot like a lever: the achilles tendon is connected to the end of the lever arm (the heel bone). When it shortens, the heel raises, meaning that the foot rotates downwards around the ankle—the fulcrum—allowing force to be exerted into the ground. Because every action has an equal and opposite reaction, force also travels in the exact opposite direction: into the calf, parallel to the calf bones.

Achilles-tendon-function

Because of the properties of the muscle-tendon system, this results in a trade-off. If you increase the length of the lever arm—the distance from the ankle to the heel—leverage increases, meaning that the calf muscles have an easier time pulling on the lever and causing the foot to point.

However, this also means that the tendons work more like a rope and less like a spring: The elastic fibers that make up the tendon have to be aligned with the direction of force in order to store that mechanical energy. If the lever is longer, the achilles tendon is at a greater angle to the direction of force, and therefore less capable of storing mechanical energy.

In other words: greater leverage = less energy return. When your skeletal structure compels you to use your muscles more (resulting in stronger muscles), you also have less energy return, which is a critical component of running economy.

The reason that the novice runners in the Runner’s World article have stronger muscles may have less to do with the fact that they’re untrained and more with why they’re untrained. Perhaps one of the reasons is that they are not dimensionally prediposed to train running. Supposing this is the case, you might look at their bodies and find that they are built for leverage, not for energy return.

You might. A longitudinal—long-term—study would confirm this (or not). If the untrained runners started training, would their running economy get better? According to the abovementioned study, not really—or at least not completely: the study estimated that 56% of running economy could be accounted for by heel length alone. In addition, the runners they looked at were all highly trained (and had comparable running performance) and their running economy still varied by 20-30%.

(This also means that while longer heels contribute to a lower running economy, they do not necessarily contribute to lower running performance. The human body has many faculties, each of which contribute differently to performance. Energy return is only one of them).

One thing is clear: as a collective, we need to be a lot more careful with the advice that we give runners. As I mentioned above, what does “strength training” mean, and what exactly are we recommending that runners do, if we make such a suggestion? The skeletal mechanics of the body (let alone the possible interpretations of the phrase “strength training”) means that the same advice given to two different runners can have very different ramifications—or worse yet, none at all.

Tendinopathy, musculoskeletal characteristics, systemic strategies, and running.

I came across a very interesting research article titled Running Biomechanics: Shorter Heels, Better Economy. Evidence is presented that running economy is determined by supposedly immutable factors in the athlete’s musculoskeletal structure, such as the moment arm of the achilles tendon, which refers to the distance between the achilles tendon and the ankle joint, which serves as the fulcrum of rotation. The evidence presented suggests that greater running economy—the amount of energy stored in the tendons, to be used in the next step—correlates with a shorter moment arm far more strongly than with other factors such as  lower leg volume or VO2 (a given rate of oxygen consumption). This has serious implications for the advice given to runners on how to improve their running economy.

Moment-ArmTakeoffAchillesTendon

The authors conclude that 56% of the variation in running economy between runners could be predicted by the moment arm of the achilles tendon. This is interesting, considering that other studies suggest that there are 20-30% differences in running economy even among elite athletes. The study, which selected highly-trained, competitive male runners as participants, corroborates these findings.

This body of data suggests that, by and large, training does not affect running economy, when running economy is a function of the body’s skeletal configuration. What does this mean? That when it is up to the physical characteristics of someone’s bone structure, changes to running economy cannot be easily made. Because the achilles tendon moment arm (which corresponds to the distance between the ankle joint and the heel bone) is fixed in adults, the abovementioned 56% in variation is also fixed.

However, factors that aren’t skeletal could affect running economy—factors such as poor muscle coordination and imbalance. For example, one of the most common problems in amateur runners is stiffness of the soleus and gastrocnemius (calf) muscles. Often, this contributes to excessive plantarflexion (pointing of the foot) and premature heel rise during the late stage of the stance phase of gait. (Heel rise should occur during pushoff phase).

dosiflexion_plantar_flexion (1)

By raising the heel, the achilles tendon moment arm increases, allowing the gastrocnemius to exert more force against the ground. However, as the above-referenced article would suggest, this means that comparatively less energy would be stored in the achilles tendon. Other research on achilles tendinopathy corroborates this, with findings that those who suffer from the condition often have a reduced activation of the tibialis anterior muscle. By and large, those who suffer from achilles tendinopathy will point the foot to decrease loading of the tendon.

It is likely that pointing the foot as a result of achilles tendinopathy is a two-pronged strategy: both the reduction in tendon loading and the increase in achilles moment arm contribute to maintaining a functioning system. In light of the abovementioned research, this increase in moment arm means that force exerted into the ground is achieved through active muscle contractions of the soleus and gastrocnemius, rather than passive energy storage in the achilles tendon. By offsetting the production of power from the tendon to the muscle, the limb can remain useful in a suboptimal state.

This means that there is no single way to improve running performance. In fact, unless you have severely impaired biomechanics—which, granted, is more than commonplace in modern runners—there is nothing much you can do about your running economy. But unless you already use your body perfectly, there is no point in worrying about a large achilles moment arm. And if you already do use your body perfectly, there is no point in worrying about it either: you’ll simply end up developing other faculties, such as the aerobic engine, as your body seeks to achieve greater speed and endurance.

In Running Science, Owen Anderson compares Steve Prefontaine and Frank Shorter, writing that even though both athletes had very similar times in the 10,000 meter race, Prefontaine had a markedly higher VO2max (maximum volume of oxygen consumption per minute) than Shorter.   Anderson’s analysis is that Shorter had superior biomechanics, while Prefontaine had to develop greater aerobic capacity. However, in light of the presented evidence (and a cursory glance over both athletes’ physiology and body type), it is likely that Shorter had musculoskeletal advantages over Prefontaine, such as a reduced achilles tendon moment arm.

Steve Prefontaine
                   Steve Prefontaine

Concretely, this means that faulty biomechanics aside, certain runners will benefit more from particular kinds of training than others. For example, a runner with a huge achilles tendon moment arm may benefit more from weightlifting and muscle power exercises, particularly those that develop the tibialis anterior, allowing for ankle stabilization during the landing phase at greater ankle dorsiflexion than runners with a smaller achilles tendon moment arm: as mentioned above, dorsiflexing the foot reduces the achilles moment arm and increases loading (which is why those with achilles tendinopathy avoid it).

Runners who have to increase dorsiflexion to a greater extent for a given running economy will still be relying on more muscle power than those who don’t, at least in some fashion: the moment arm of the tibialis anterior (which dorsiflexes the foot) increases throughout dorsiflexion. In other words, this will offset the need for muscle power from the rear muscles to the front muscles, at least in the calf region.

It’s likely that the same biomechanic advice—advice on how to develop running economy—won’t be equally useful for two different runners. Although running economy will be largely a function of achilles tendon moment arm, running speed, endurance, and overall performance is not. Runners should study their bodies (or get studied by an expert) to see what kinds of training will help them develop their race performance.

Keep in mind that running economy is not the same thing as running performance. Prefontaine and Shorter’s comparison should tell you that. However, certain people have attributes that favor specific skillsets. Some people have great muscle power, others have great economy. Lately, running trends have been focusing too much on the energy-return properties of the body—so much so that runners are either alienated or forget that the body has other properties. The body is always more complex than the latest trend says so. And even if the latest trend does not validate the attributes that we should develop to make us better runners, it doesn’t mean those attributes aren’t there, or are somehow less important. The human body is an extremely complex machine, capable of achieving great performance through many different avenues. With a bit of study, we can figure out what those are.

Deconstructing “flexibility.”

Throughout our lives, most of us have heard that it is extremely important for us to be “flexible,” for a variety of reasons. Off the top of my head, I’ve been told that flexibility is important to make movement easier, so that my joints don’t deteriorate, and so that I don’t get hurt lifting heavy objects. This is excellent advice. But the problem is that basically all of us go about achieving greater flexibility in exactly the wrong way: by stretching, or more specifically, static stretching. And that is because we don’t understand the concept of flexibility in a mechanically useful way.

One of the main physiological problems of westernized people is poor biomechanics—a phemonemon that basically boils down to the idea that the muscles across our bodies are badly synchronized. Simply stated, they don’t know how to work well together, and when they are subjected to trying circumstances (such as exercise or age), the mechanisms freeze up and become damaged.

For some non-athletes, stretching may help initially. In a very low-risk environment, stretching helps these frozen mechanisms because it increases the net joint range of motion (ROM). This means that the joint can go just a little more before it gets hurt. But that doesn’t solve the problem: the muscles haven’t become synchronized; we’ve only ameliorated the symptoms because we’ve created ROM by isolating the muscles (due to stretchier tendons and weaker muscles), instead of developing their synchronization.

This is a classic case of a systems management problem called “shifting the burden.” We have a perceived need to increase flexibility (because of a particular set of assumptions), and we shift the burden of flexibility away from synchronization and towards isolation. When the symptoms ameliorate, we think that the problem is solved, and we subject it to higher-risk circumstances, such as sports. Soon, we find ourselves caught in an unending roller-coaster of injury.

We can solve this problem. But in order to do so, we must deconstruct our notions of “flexibility.”

Continue reading Deconstructing “flexibility.”