The Efficiency Rule

Stay the CourseHappy New Year! ‘Tis the season for a new resolve to do things better. For many of us, a better 2019 begins with doing more. But for those with limited time and energy, there’s only so much ‘more’ we can do. Instead, we endeavor to do what we are already doing better.

To run better without running more is to be efficient. Given the limitations of time and energy, efficiency is the gold standard for both improvement and peak performance, especially for those of us who are already running pretty far and fast. Efficiency is king.

[Author’s Note: In technical scientific terms, ‘efficiency’ refers to the percent of expended energy that is used for doing work (as opposed to energy lost as heat). Speed or distance per unit of energy is referred to as ‘economy.’ However, because economy has a financial connotation for many people, we use the term efficiency instead.]

What if you cannot run very frequently, far, or fast? Then injury has probably derailed your running. Given that a full three-fourths of all runners will incur some sort of injury each year, the odds are strong that most of us have been recently tripped up and slowed down by an ache or pain.

What if fast and healthy running were truly linked? Beyond the benefits of consistent running, what if top speed and injury prevention were two sides of the same coin? In fact, this is the essence of efficiency: minimal body stress and maximal propulsion.

The Frustrations and Failures of Running Research

What does the research say about this? To begin, it’s been a long and convoluted road. Academic researchers have finally caught on to the notion of stride efficiency in running injury. Biomechanists and orthopedic clinicians have been studying running injury for decades. However, that injury incidence hasn’t budged from a supermajority of runners each year is disappointing (if not embarrassing) for medical professionals, coaches, and runners. ‘Evidence-based’ interventions of a certain strength routine or a miracle stretch have hardly scratched the surface of our collective injury epidemic. After years of repetitive failure, researchers are beginning to put down the resistance bands and stretch routines, and instead examine how we run.

But if research has let us down for this long, who is to say that research-based running-mechanics guidelines will be any different? Perhaps the answer lies in how to interpret and apply that research in the real world.

Correlation Versus Coaching: Applying Injury Research to Your Running

Most quantitative research is based the relationship–a correlation–between two measures:

  • Some measurable aspect of a runner. Examples include range of motion, strength, or a quality of movement (heel strike versus forefoot landing).
  • An outcome measure. Examples are the incidence and duration of pain and injury.

For example, research has shown that hip-abductor and external-rotator muscle weakness are correlated with lower-extremity injury. Importantly though, such associations do not imply causation. It’s still possible to have weak hips and be healthy, just as it’s possible to have strong hips and get injured. However, correlations are often all we have to go by in establishing root causes.

Now what? Research has connected these two dots:

  • Weak hips
  • Injury

For academics, the next logical question is, how do we make the hips stronger? Back to the research, where we endeavor to find the most effective strength exercises. The best exercises to activate and strengthen hip muscles, as determined by laboratory studies, are then recommended.

Therefore, if weak hips correlate with injury and exercise routine #1 creates the strongest hips, then exercise routine #1 must prevent injury. Right? Not really. It doesn’t work, and we all know it because we’ve tried it.

Evidence-based recommendations are based–and lean too heavily–upon correlations. It may correlate with weakness, but running injury is the result of a complex and often messy amalgam of factors. It’s a major stretch to ascribe injury to a single variable. It’s an even bigger stretch to believe that performing an isolated strength or mobility exercise will completely rectify a complex injury pattern. That is why your clam-shell routine never really cures that knee injury, no matter how many sets you do a day or the thickness of your stretch band (and backside muscle).

Researchers have caught on, and now they’re finally studying stride mechanics. Great! But hold on. Before you get too excited, let’s see about our old problem, correlation. The most promising body of running-stride research today is on stride cadence. This variable looks at how many steps per minute we take when running. This correlates with running injury because the slower the running cadence, the longer we spend on the ground, and the greater the energy absorbed by our legs. Today, both cadence and ground-reaction (landing) forces are easily measured on high-tech treadmills. As such, numerous studies have demonstrated that slow cadence causes increased ground-reaction forces and increased ground-reaction force correlates with injury. Thus, faster cadence must prevent injury.

Trusting that correlation, how do we best increase cadence? Unfortunately there is no clear consensus, other than ‘move your feet faster,’ which seems dubious. Current research recommends running with a metronome (or listening to songs with a 180-beats-per-minute tempo–the evidence-based correlate for efficient cadence), but there is no specific strategy for how to more quickly strike the ground. Nor is there any discussion on how ‘faster feet’ might affect the rest of the stride. Anyone else skeptical? Something’s missing.

Efficiency is Peak Performance and Minimal Strain

It may be time to cast aside the medical-research hat and put on the athlete/coach cap and think about efficient running. If efficiency is the greatest speed or distance per unit of energy, then efficiency also implies minimal wasted energy. Injury is most strongly correlated with high landing forces or energy that is bashed into the ground (and the legs) rather than used for propulsion.

Thus, efficiency is now a compelling argument for both injury relief and prevention, as well as peak performance. Efficient running is the fastest and lowest-stress running. Now we have a worthy metric.

The Efficiency Rule Defined

Based on the theoretical connection of minimal strain and maximal speed, I put forth the ‘Efficiency Rule,’ which is defined as: “Any running-stride adjustment that sustainably relieves pain must also make you faster.” To be clear, relieving pain means decreasing stress, strain, or another objective force measure.

The Efficiency Rule implies that in order to create a running injury there is an efficiency drain, a place where energy intended for propulsion is being absorbed excessively by the body. Thus, by virtue of the law of conservation of energy, decreasing body stress increases the amount of available energy for propulsion. This means we have a new standard for any running-stride optimization: efficient, low-stress running will result in faster running.

Efficiency: Sustainability and Performance and why Barefoot Running Failed (Most of) Us

Within this definition are the two key operators of sustainability and performance. Both must be satisfied in order for a running intervention to qualify under the Efficiency Rule.

Performance relates to measures of velocity. Either our top speed or our overall endurance at relatively high speeds will improve with a strain-reducing running strategy. We will discuss this in more detail below.

Sustainable interventions:

  • Make pain go away and keep it away; and
  • Must not create a different strain or injury (in the longer term).

Every intervention has second-order effects, which are side effects that emerge as a result of the adjustment. In the case of cadence adjustment, what second-order effects could possibly arise from simply ‘moving your feet faster?’ (Spoiler alert: many.)

Likewise, the demise of the minimalist-footwear boom of the mid 2000s is an example of both the limitations of correlation as well as unseen second-order effects. Indeed, runners do land ‘softer’ in more minimal shoes. (And, as we’re finding out, the converse is also true.) But rather than automatically adopt an efficient (‘fast’) stride, what most minimalist runners did was shift that strain from bone and joints to soft tissues, thereby overloading the calf and lower-leg muscles. This caused a strong second-order effect of increased muscle injury that turned many away from minimal shoes. Thus, arbitrary stride changes are seldom enough to create long-lasting improvements in injury prevention.

I used to joke that you could cure a foot injury if you ran on your hands and knees. Indeed, simply changing the load on the foot will allow it to heal, right? But does this satisfy the Efficiency Rule? Let’s see:

  • Sustainability. Is running on the hands and knees sustainable? What are the second-order effects?
  • Performance. What is one’s peak velocity and endurance while hands-and-knees running?

This may seem silly and irreverent, but here’s a real, stranger-than-fiction example. A recent study demonstrated that significantly less landing forces were incurred in the legs… if you didn’t run. That is not a typo. Performing “grounded running”–a style of movement akin to speed walking where one foot is always on the ground–is significantly less stressful than “aerial running,” also known as… running!

This is a classic example of an intervention that blatantly fails the Efficiency Rule:

  • Sustainability. Will speed-walk-running sustainably relieve pain and prevent injury? Probably (especially for lower-leg, ankle, and foot pain).
  • Performance. Will speed-walk-running make you a faster runner? Absolutely not. The float phase is crucial for both top overall speed and sustained top endurance speed. (This is not to say this isn’t a useful technique, but the majority of runners want to run, are capable of running through the air, and wish to continue doing so.)

The same goes with cadence training. Simply moving your feet faster is a strategy that does not satisfy the Efficiency Rule:

  • Sustainability. Faster cadence may decrease ground-reaction forces, but second-order effects may include decreased hip mobility (which can increase hip and hamstring strain), among others.
  • Performance. Moving your feet faster at the expense of hip mobility (and without optimizing other variables) will, over time, decrease both top speed and endurance.

Thus, the bar has been raised on how to relieve pain. It’s not good enough to simply move differently. We must move better.

The Sight and Speed Test: Look Fast and Be Faster to Run Efficiently

If the Efficiency Rule mandates faster running from whatever stride adjustment we make, the easiest way to assess fast running is by visual inspection. This is the essence of coaching. Across all sports, there is a fairly narrow standard of ideal technique for any given movement (individual quirks notwithstanding). Skilled coaches know efficient movement and they know their sport-specific standards very well.

As such, the standard for any new running-stride technique is simple. Does it look good? Do you look like a ‘good, fast runner’ doing that new thing? When it comes to posture, pawback, and arm swing, you probably do! (But for speed walking, hyper-cadence shuffling, or bear crawling? Probably not!)

How it feels and how difficult it is, is initially irrelevant. Anything new feels and is initially more difficult due to neuromuscular novelty. This is typical of new learning. With repetition, both the feel and ease greatly improve. But in the short term, if it looks good, you’ve nailed the first step. This is why, as a coach-clinician, I always employ a video tablet to record and immediately provide visual feedback to my clients. (Real-time feedback is most ideal.)

The second metric is speed. Does your stride adjustment make you faster? Like visual appearance, speed improvement is usually immediate. Optimal alignment, leg motion, and arm movements will result in immediate improvement in both top-end speed and endurance. That said, you may not have the intrinsic strength and endurance to maintain it for very long, but like fitness, that new stride ability will develop with repetition (and specific exercises and drills).

Summary

Injury and performance are tightly intertwined. Energy that creates injury is energy robbed from performance, and energy preserved from the legs is used to propel. The Efficiency Rule is the litmus test for any injury-prevention strategy because it aims to redirect energy from strain to speed, from frustration to the finish line–fast!

It’s not only logical but enormously hopeful. For me, it’s both exciting and deeply rewarding to help a runner not only overcome and prevent injury, but to also get faster at the same time. Each of us runners should be equally hopeful and shoot for the Efficiency Rule standard. We should endeavor to make an adjustment that not only gets and keeps us healthy, but also makes us faster. Such a double-barrel effect is something worthy of our resolve!

Call for Comments (from Meghan)

  • Have you ever intentionally or unintentionally changed an element of your running stride that made your running both feel better and become faster?
  • Alternately, have stride changes ever resulted in unintended, negative side effects?
Joe Uhan

is a physical therapist, coach, and ultrarunner in Eugene, Oregon. He is a Minnesota native and has been a competitive runner for over 20 years. He has a Master's Degree in Kinesiology, a Doctorate in Physical Therapy, and is a USATF Level II Certified Coach. Joe ran his first ultra at Autumn Leaves 50 Mile in October 2010, was 4th place at the 2015 USATF 100K Trail Championships (and 3rd in 2012), second at the 2014 Waldo 100K, and finished M9 at the 2012 Western States 100. Joe owns and operates Uhan Performance Physiotherapy in Eugene, Oregon, and offers online coaching and running analysis at uhanperformance.com.

There are 13 comments

  1. Ric Moxley

    Every time I see that the article is going to be written by Joe Uhan, I know I need to read every word, and carefully. It’s always educational, and always immediately applicable. Good stuff. Thanks

  2. David Oppenheim

    This was my first article read w/the Samsung Fit app. Personally, the article contained a LOT of considerations and information that was distilled and presented on a basic level for understanding and engagement to keep reading. As a tall runner that got Achilles tendinitis from marathon overtraining 34 yrs. ago, article like this would have been asset to have. It still is. My eyes will be peeled for articles by this man. Thanks for the good read.

  3. Don S

    Joe,
    Great article. I think this this a brilliant framework for evaluating interventions. I feel though, that I need to defend the enterprise of empirical science a bit. I think that you have placed the blame of the failings of exercise science on the wrong culprits. Correlations are simply information, and being ‘evidenced based’ is necessary for true knowledge advancement. The fact that it is possible to have weak hips and be healthy or strong hips and get injured, does not refute a causal link between hip-abductor or external-rotator muscle weakness and lower-extremity injury, it suggests that injury has many other potential causes that may or may not interact with hip strength. The problem, then, is not in trying to interpret the patterns of correlation, but that the research programs you point out are being far too reductionistic. That is, instead of appreciating the complex network of causes the may lead to injury, as a coach might, they hypothesize a much too simple set of possible, independent mechanisms. As you suggest, what is required is a much more holistic approach that incorporates deep system-specific knowledge to interpret the patterns of correlations in these systems. We won’t make progress by ignoring data (correlations) or abandoning the goal of achieving evidence-based conclusions (which is not something you suggested, but a reader might inferred if reading too hard between the lines of your critique).

    1. Joe Uhan

      Don-

      Thanks for the thoughtful reading of the article, as well as the equally thoughtful response.

      A couple nuggets:

      1. There is no causal link between hip weakness and injury. Causal (vs mere correlation) is a heavy statistical burden that, to my knowledge, has yet to be overcome.

      2. I am being a little reductionist (“I’m picking up your sarcasm” / “I should hope so, because I’m laying it on pretty thick” https://www.youtube.com/watch?v=2mSd5t2n3ck ).

      The fact is, many of us practitioners (either medical or coaching) are getting worn down by the following [non-]dialogue:

      Us: “We believe that X causes Y”
      General public: “Where is the research study?”

      The reality is two-fold:

      As Nassim Taleb says, “Practice drives theory”. It’s the practitioners (The Doers) that, through trial and error, and formulation and reformuation, find the most sustainable and best practices. As a coach with an interest in both health and performance, I have unique “skin in the game” to be responsible to improve one…but not at the expense of the other. Research findings driven solely by academics (or academics and [very-] part-time clinicians) have zero skin in the game to deliver recommendations that satisfy the Efficiency Rule.

      Meanwhile, modern research consumption has trained the layperson (e.g. the runner, the person that matters) to:

      1. Question any recommendation that is not found bound within a research journal

      while simultaneously:

      2. Accepting with blind faith any and all published findings.

      Matt Laye and I have had, for a long time, an idea of writing a piece on “Research Study Literacy”, to help each other understand the true weight of research findings. This piece serves as a preface to that: establishing the highest standard for any sort of “evidence-based” recommendation for runners.

      Lastly, within the notion “Evidence-Based Practice” are three pillars:

      1. Research studies.
      2. Clinical experience
      3. Patient values

      The true value of The Efficiency Rule is that it satisfied all three of those pillars.

      Thanks again for the read and comment

  4. Mike D

    This is a great article, but not everyone has time or can afford a coach. How do you recommend individuals without access to coaches can still apply this method to improve efficiency?

    1. Joe Uhan

      Mike-

      Thanks for the question.

      Like other aspects of running, becoming a “student of the sport” is crucial in improving efficiency. That said, it’s tough, because:

      A. there is relatively (disproportionately) less acceptance (/interest) in stride efficiency as a crucial – and changeable – aspect of running performance.

      B. there is scant material out there that bridges the gap between the heavy adademics (of research lab biomechancis) and The Athlete.

      Part of my mission as a scientist and writer is to:

      A. convince you that efficiency is key (if not King), and
      B. provide comprehensible and readily applicable tools for runners.

      This (and, I hope, all my writing) is part of that mission.

      Check out the other Stay the Course offerings. Also, poke around on instagram; there’s some folks out there putting out some good visual content of stride efficiency!

      And stayed tuned: there’s a book project from me “on the way”….

  5. Jamie

    Thought-provoking article. Always appreciate the opportunity to get your insights, Joe, and I find myself nodding along with your argument that the key to running healthier is running better (and vice versa).

    In the interest of developing the conversation, here are a couple of thoughts in counterpoint to the perspective you’ve offered here.

    1) Most running injuries need to be understood in terms of relative, not absolute, durability/efficiency. Elite athletes tend to have much better biomechanics than casual joggers, but they can still have high rates of injury, because the stress that they impose upon their bodies is very high even in relation to their very high levels of fitness and stride efficiency. What gets us hurt, in other words, is not simply the mechanics of our stride, good or bad as they may be, but the specific stress that we impose upon our bodies, relative to our capacity to handle that stress, and relative to our capacity to recover before further stress is imposed. (Or, to put it another way, our capacity to handle not only the stress of a specific effort, but whatever stress we may carry over from one effort to the next, that accumulation of stress being the very essence of endurance sports.) In this way, running injuries need to be considered not only as a matter of efficient or inefficient stride mechanics, but of sustainable or unsustainable training practices. This is not to discount the importance of stride efficiency (not at all!), but I would argue that the dynamics of running health and performance need to be understood in somewhat more nuanced and holistic terms.

    2) With point number 1) in mind, the critical diagnostic question becomes not only “How do we develop mechanical inefficiencies that impair our health and performance, and how can we develop greater mechanical efficiency such that our health and performance are improved?”, but “Why do we impose stresses upon our bodies that our bodies are not able to handle, and how can we make our training practices more sustainable, and so, in the long run, more efficient?” Very, very, very frequently, I would suggest that the answer to the first part second question is essentially mental, emotional, or psychological in nature. So, to go back to the problem of causation, an unsustainable training practice may lead to, say, a bout of ITB, but there is a very real sense in which the cause of that injury is, say, impatience or insecurity or what have you.

    3) With point 2) in mind, it seems necessary to be somewhat more nuanced in the way that we connect “running better” and “running faster.” Frankly, one of the main causes of injury for runners who are in any way competitive (including those of us who are primarily competitive with themselves!) is the desire to get faster at a faster rate than our bodies can handle. So, it’s important not to confuse “running better will help you run healthier and faster” with “faster running is better running.” I don’t mean to imply that you yourself are confused about this point, but I do suspect that some runners may be tempted to misinterpret your message in this way. (And for myself, I know that some of the key practices that help to make my running more efficient and my training more sustainable for me have comparatively little to do with running fast.)

    Thanks again for a fascinating read.

    1. Joe Uhan

      Jamie-

      Thanks for the equally thoughtful response. A few comments to yours:

      >What gets us hurt, in other words, is not simply the mechanics of our stride, good or bad as they may be, but the specific stress that we impose upon our bodies, relative to our capacity to handle that stress, and relative to our capacity to recover before further stress is imposed.

      Agree, 100%, which is why I’ve written these two posts:

      https://www.irunfar.com/2014/01/metabolic-concepts-in-return-to-running.html
      https://www.irunfar.com/2017/12/painting-bridges-chemical-stress-in-a-running-injury.html

      So while I agree, I will say that mechanical stress is 51% and chemical is 49%, if only for the latency of effect. Seldom do new runners immediately succumb to a pure load-vs-capacity imbalance — this takes time to “fill and overflow”; however, the latency of mechanical inefficiency is extremely small.

      As such, mechanical efficiency is priority one in my opinion.

      >Very, very, very frequently, I would suggest that the answer to the first part second question is essentially mental, emotional, or psychological in nature

      Again, I agree, but again, I say this is a more latent issue. The new runners I encounter often start running to:

      * get in shape
      * get involved (socially)
      * achieve a (usually small, realistic) goal

      Only after tasting the sweetness of those payoffs, do I start to see the “psych imbalance” of NEEDING that running reward, and having that need create a stress-rest imbalance.

      However, I see brand-new runners get injured all the time, with extremely high correlations to very poor stride efficiency.

      >it’s important not to confuse “running better will help you run healthier and faster” with “faster running is better running.”

      This I agree with, 100%. Finding efficiency across all “speeds” (/intensities) is the highest priority. Indeed, most novice or intermediate runners, run “too hard” (at least in physiological intensity) across all distances, and the majority of runs. Thus, emphasis needs to be placed on velocity generation per-unit-[less]-intensity: learning to run medium speed with very low effort. This is what the veteran elite runners of our sport do very well.

      Thanks again.

  6. Matt Laye

    Joe – I’m still up for that article discussing the appropriate ways we can use the scientific literature in combination with our own experiences and those with experience (such as yourself) to better our running experience. There is also a new organization that is looking to improve the transparency and analysis problems currently associated with publication. I think the readers would enjoy hearing about the questionable research practices which exist (likely because we scientists don’t have the skin in the game).

    I like the framework that you have set forth and think that it also applies not only to how we change our strides with practice, but how our stride changes over the course of a race. For instance, ultrarunners become less efficient from a metabolic standpoint (oxygen use) and use a shorter stride length (the ultra shuffle) with the same speed. Or “more strain” “same gain”.
    When we enter this part of a race or long training bout we become more likely to hurt ourselves as the strain is dissipated to areas of the body underprepared to handle it.

    Perhaps your clinical experience can help clarify something for me. When novice runners and experienced runners get injured have they both experience efficiency drain in the same way at the same rate? I guess I’m asking do all runners get (overuse) injuries for the same reasons?

    In terms of the falsifiability of your rule. At what point would you say the rule does not hold. How long must a runner do something that increases strain and speed without injury? A training cycle? A year? A lifetime? It seems like it could be a very hard rule to disprove. I can think of muscle and tendon stiffness increasing (which is an increase in strain?) as a positive adaptation in terms of the ability to move faster to a degree (more like an inverted U curve). There is likely some strain necessary for the adaptation to run faster, but a point of diminishing returns or injury that is individual for each athlete. I guess that is the job of the do-er to figure it out. :)

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