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Thursday, December 06, 2007

Running Economy Introduction

Zersenay Tadese - the most economical runner in history?

Well, a provocative headline for sure, but that's pretty much what a SCIENTIFIC study has suggested after measuring the oxygen consumption and running economy of the World Cross Country and Half Marathon champion recently! The study, published just the other day in the British Journal of Sports Medicine, and performed by Carl Foster and Alejandro Lucia, found that Tadese has one of the best (if not THE best) running economies ever measured. That is, he uses LESS oxygen at the measured running speed than any runner reported before him.

I would not question the study for a second (well, not too critically, anyway), as Foster and Lucia are both excellent scientists, with great records in the field. Foster is famous for his modeling of pacing strategy and performance, while Lucia has been one of the leading researchers in cycling performance, doping and the physiology of performance. So some credible names, and a fascinating paper, for sure!

We are always on the lookout for interesting news stories here at The Science of Sport, and we do our best to take sports news and exaplain the science behind it. But this particular story is both newsworthy and science-worthy at the same time, and we say thanks to George (a self-described devoted reader of the blog) for bringing it to our attention!

Introduction of a new series - running economy

What we would actually like to do before we analyse this paper (and Tadese's new claim to fame) in tomorrow's post, is to use this really great story to introduce a new series and discussion around this concept of running economy. I seem to recall that about three months ago, there was a whole spate of articles on running economy - for some reason, it suddenly shot to prominence and a number of widely read newspapers started writing about it as though it was the very latest thing, even though we've known about its importance for about 30 years. And even back then, we considered the prospects of some posts about running economy, but they got kind of swept away by the heat of Chicago and the racing in New York. Well, no time like the present to go back there!

Running economy 101: What is the big deal?

To begin with, running economy in humans is probably analogous to cruising-efficiency in a car (not entirely, but we'll get there!). If you think of a human, we can measure the maximum volume of oxygen that can be used, and this is called the VO2 max or VO2 peak. The problem is, for most running events (certainly above about 5000m), runners don't use this "maximum" amount - they are sub-maximal. And so therefore, a more important measure becomes the volume of oxygen that is used up when the runner is going at a sub-maximal speed.

So to return to our fuel analogy, it's saying that the car is cruising along at a speed lower than maximal, and we're interested in how much fuel it uses per kilometer.

Now, there is plenty of reason to think that running economy is very important. There used to be a perception, which still exists in many circles, that the be-all and end-all of running performance was the VO2 max value. In other words, you'll still find people who think that the runner who has the highest VO2 max is the guaranteed winner. Many runners who have been tested wear their VO2 max like a badge of honour if it's high, whereas they hide it away if they think it's low, such is the importance that has been placed on this measurement.

And of course, it is still crucial that a world class runner have a higher than average maximum ability to use oxygen. So you'd be very hard pressed to find any world-class runner who has a VO2 max lower than about 70 mL/kg/min (this is the unit for VO2 max, by the way - it's a volume in mL, expressed relative to body weight over time). Your typical moderately fit male, weighing about 80kg, would have a VO2 max of about 50 to 60 mL/kg/min, and a fairly well trained athlete might hit the mid 60's, with the better ones being higher than this, into the 70's and 80's. So there is a "GENERAL" trend for the fitter, more highly trained athlete to have a higher VO2 max (although we would argue that is a consequence and not a cause of performance).

But then there's a catch - Maximum is not the deciding factor

The reality however, is that you don't always get this nice, uniform increase in performance with an increase in VO2 max - often times, a guy with a VO2 max of "only" 75 ml/min/kg will beat a runner whose VO2 max is "superior" at 85 ml/min/kg. And so clearly, there is more at play than simply the size of your lungs, your heart and the muscles maximum ability to use oxygen.

Intuitively, you recognized that this makes sense - as we pointed out above, because 10000m races are run about 90% of VO2 max, and marathons are run at 80 to 90% of VO2 max, there is room for difference because it's the runner's ability to use the oxygen most efficiently that contributes a substantial amount to performance.

So that's where running economy enters the equation. Whenever you read a book on this subject (be it Lore of Running, or any other text), you always see the concept of running economy introduced in this way - it's the excuse for the "little guy" (in terms of maximal oxygen use, anyway), beating the big guy!

Considering how important running economy seems to be, it's apparently been ignored in the literature. Last year, in October, a seriously high-powered gathering of exercise physiologists and scientists gathered in Chicago for a conference on Marathon Medicine and Physiology.

And at that conference, Carl Foster, one of the authors of the Tadese paper, discussed the role of running economy in performance. He suggested that the science has "ignored running economy" to date, despite knowing about it for 30 years, and as a result, relatively little is known about the topic.

It therefore seems like a nice, juicy and interesting topic to tackle in a series, and so what we'll do over the next couple of weeks is take a look at running economy. We'll begin with an analysis of the study on Zersenay Tadese, which began this post, then we move onto the importance of running economy, the factors determining running economy, and methods that you can use to improve your running economy, and hopefully performance.

So join us over the next few weeks as we get into what could be a very interesting discussion!

Ross

16 Comments:

Ryan said...

I can think of many reasons why V02 max doesn't directly correlate with running performance. Lactate threshold is an important one, but the thing I think is most often ignored completely is anatomy. An easy example I can think of is imagine Runner A and Runner B: both have V02 max of 75. Both are the same height and weight, and both have the same leg turnover rate, and both have the same lactate threshold. Runner A has a stridelength that is 2 inches longer than Runner B, so Runner A should win. But that isn't always the case either, there is a mental factor and a proper fueling factor as well! There are just way too many variables.

Ross Tucker and Jonathan Dugas said...

Hi Ryan

Lacate - mmmmm...there's an interesting one, and definitely a topic for a future post or series. The concept of lactate threshold is hugely in doubt now, and there's a real perception that it might be an artefact of the method by which it is measured. So much so, that there might not be a threshold at all!

The whole lactate "myth" is very interesting indeed, and is definitely something we need to consider for the future.

As for your analogy, you're quite right, the stride length is important. I'm not sure how I follow that this is related to anatomy, however? You could very easily achieve a different stride length with identical anatomical features. And in addtion, I'd question HOW that longer stride length is achieved? It would imply greater muscular work on the part of the athlete, or their leg length would be different, which might be what you're getting at?

But stay tuned, because the Zersenay Tadese study might actually reveal that running economy and anatomy are in fact related variables! In otherwords, running economy doesn't ignore anatomy...

More on that tomorrow

Cheers
Ross

Ryan said...

Yes, what I'm getting at is Runner A's legs are longer, giving a longer stridelength. But another example is Runner A and Runner B are twins, identical in anatomy. Runner A's stridelength is 2 inches longer, same leg turnover, but Runner B is always faster? Well, Runner A is overreaching with his stride and hitting his heels, braking on every stride and slowing him down. I'm just trying to point out that its not just physiology that predicts speed, there is also physics.

Ross Tucker and Jonathan Dugas said...

Hey Ryan

Yup, acknowledged. Though I don't think that anyone was ever trying to say that things like physics weren't important to the question of performance in this post.

But just to touch on your example, if Runner A and B run with the same stride turnover and Runner A has a longer stride length, then it's absolutely impossible for Runner B to be faster. Even if Runner A is braking when he lands, the fact that his turnover and length are longer will add up to faster running.

For example, if both take 90 "strides" per minute, but Runner A covers 2 m per stride, and Runner B covers 1.95m per stride, then Runner B can't win - somewhere, something has to give. So if Runner A is over-striding, then you'd see it in the stride length or stride turnover. You might, for example, predict that he is overstriding and at some FUTURE point, may slow down and then either his turnover or stride length will drop off lower than in Runner B. But having taken this 'snapshot', it's not possible.

And also, you'd pick this up in running economy - if Runner A was overstriding, you'd find a reduced running economy, because energy is being wasted to create the longer stride, and to overcome the braking when landing as he over strides. So then the physiology mirrors the physics, or vice versa, and they're compatible.

Ryan said...

Yep, you're right. I made a mistake with my example. I'm not trying to argue with you guys, I'm in agreement that there's more to it than V02 max.

kevin said...

When you talk about running economy, is it possible that running too slow _ perhaps to preserve energy during a marathon or a hot long run _ wouldn't your running economy be off. For instance, I feel great when I'm running what people call a "tempo run." And for me, on flat ground with no hills, thats about an 8:15 minute mile. And im feeling good, my stride feels good. And my last mile in the run (usually about 8 miles) is usually the fastest. But, when i do a long run, i chop my steps to go slower and the whole run seems like a struggle and never feel as strong as i do during the tempo run. Is this a function of running economy?

Bruce said...

Guys -

Absolutely love the site. Thanks for taking the time to post such interesting topics and discussions.

I don't want to stray to far off the subject here, but one thing that always confuses me is the usage of the terms "economy" and "efficiency." Economy is explained well in this post, although the work "efficiency" is also used:

" it's the runner's ability to use the oxygen most efficiently that contributes a substantial amount to performance."

From your perspective, can you give us definitions of both terms, perhaps as to how they are used in both cycling and running studies/tests?

Thanks!

Ross Tucker and Jonathan Dugas said...

Hi Bruce,

Thanks for the positive feedback, and we are really pleased that you are enjoying The Science of Sport so much. Even more so, it is great to have you joining the discussion here!

Funny you should mention these terms "economy" and efficiency," as Ross and I were chatting about perhaps including this point.

The problem is it can get quite technical, and it might detract from the overall aim of the series. However, seeing as how there is some definite reader interest I think we have to work it in there now.

The teaser or precursor is that efficiency is a ratio of how much mechanical work you actually do (the numerator) and how much chemical energy you expended to do that work (the denominator). Normally the quotient of these two variables is ~20%. That is, humans are about 20% efficient.

Economy, on the other hand, refers to your oxygen usage ("cost") at a given velocity (running speed). So we would look at how much it costs you and another runner to run at six minutes per mile. In theory the runner who "spends" the least oxygen at that speed is the most economical.

Stephen Seiler (a subscriber to this blog and an Exercise Physiologist) has a good explanation of these concepts here:

Efficiency vs. Economy

I will leave it at that for now, but I hope that makes sense. Perhaps you can see how it can quickly become pretty hectic to get your mind around, but we will still try to tackle it in this series.

Thanks again for the question!

Kind Regards,
Jonathan

Half timer said...

Hi Ross & Jonathan

I look forward to having a book (the science of running) written by you. Do you plan to write one to compile the knowledge and experience in this blog?

Ross Tucker and Jonathan Dugas said...

Hi Half-timer

Thanks a lot!

Indeed we do! We'd love to put it together! If you know of any publishers....just kidding.

But absolutely, I think given the young age of the blog (8 months) and that we both are flat out with work just at the moment, it may have to wait, but when I look back over the content so far, there's a vast amount that would be challenging and interesting to compile into a book.

So hopefully someday, and some day not too far away!

Thanks for the encouraging words!
Ross

Anonymous said...

Wow, I feel like I am in a virtual classroom all I have to do is raise my hand, ask a question and Ross and Jonathan are there ready to provide answers. Thank you for taking up my suggestion to tackle running economy.
One quick question: If a runner is less "costly" wouldn't we rather say that he has high running economy? If Tadese for example "spends" the least amount of oxygen
to run at a certain pace, among all other runners tested, shouldn't we say that he has one of the highest running economies ever measured?

George

Ross Tucker and Jonathan Dugas said...

George, you're onto us. That was an error - I'm going to blame it on the long sentence, and say that I began the sentence wishing to say that he had the LOWEST cost of running, and then when I changed my mind to make it RUNNING ECONOMY, I didn't go back and correct myself!

I'll change it right now (which means you'll look like the confused one when anyone reads the post from now on! Just kidding!).

Thanks for pointing that out!

Ross

Coach Tammy said...

Hmm... can't wait for the series on LT! You guys are brilliant, and more importantly, know how to communicate at a level that a lay-person can understand. I've turned many people onto this blog, and they all LOVE IT! I don't know where you find the time, but please keep it comin'!

Ross Tucker and Jonathan Dugas said...

Hi Tammy

Thank you so much for your kind words and endorsement! It's wonderful to hear from you, and considering we set this site up specifically for the purpose of communicating science in a newsworthy and fresh way, it's especially pleasing!

Best wishes!
Ross

Colenso said...

Interesting comment from Ross about the "lactate" myth and the lactate threshold.

Speaking as an ex-physics teacher and long time runner and physical activity enthusiast of a theoretical and pedantic bent, I have been arguing with anyone who would listen (which usually meant my reflection in the bedroom mirror) since the late eighties that there has never been such a thing as a lactate threshold - if one uses the term correctly as one would use it in physics or chemistry.

As a historical aside here, traditionally, much of sports science has borrowed extensively from the physical sciences, with dare I say it, very little proper understanding of the underlying physics or chemistry. This may well be changing now, but my impression is that most sports science researchers come from a coaching, medicine or biology background, occasionally from engineering sub-disciplines, rather than from physics, chemistry or mathematics. Feel free to correct me on this if I'm overstating my point.

Now in physics, perhaps the best known modern example of the threshold is the phenomenon famously explained by Einstein in 1905 and purportedly verified by Millikan eleven years later in 1916. It's famous as the “photoelectric effect”: below a certain frequency of incident electromagnetic radiation no electrons are ejected from the freshly cut surface of alkali metals such as sodium, potassium and lithium placed in vaccuo. I say “purportedly verified by Millikan” because the strict threshold in fact only applies at absolute zero. At any temperatures above zero, in other words at all actually achievable temperatures, Fermi-Dirac statistics predict that there will always be enough electrons with high enough energies to escape the surface, even without being knocked free by a photon of sufficient energy. However, if one ignores or accounts for the Fermi-Dirac effect, then there is indeed an observable frequency threshold below which no electrons are emitted.

Ok – so that’s what in physics we call a threshold. And in fact, a moment’s reflection will confirm that is also what we mean by a threshold not only in physics but also in everyday use: a value of something below which something else does not happen or is not seen. So, is this what one observes when one measures the concentration of lactic acid in an animal’s blood or in an animal’s muscle cells? The simple answer is no. Lactic acid is produced as part of the normal metabolic process even when an animal is lying down asleep. The greater the rate of physical activity the more lactic acid is produced until it reaches a maximum level. This varies from animal species to species and from individual to individual within the species. There is no lactic acid threshold observable except for that of complete cessation of metabolic activity some time following death. The lactic acid production is not rectilinear when plotted against variables such as running speed, heart rate etc. Nor would one would expect it to be. A rapidly rising rate of a variable does not constitute a threshold. One can easily make any such plot of values appear rectilinear by determining the minimum value of lactic acid at rest and then plotting logs instead of actual values.

So, in summary, there is not and has never been such a thing as a lactic acid threshold related to physical activity.

Ross Tucker and Jonathan Dugas said...

Hi Colenso

Thanks for the comments - really interesting comparison between your field and ours! I won't claim to fully understand the physics, though I do know of the Millikan experiments!

This debate has gone on in exercise science for a long time. I agree with you that part of the problem is this 'borrowing' from other fields without fully appreciating the true definition of the terms being used. I suspect that as the field continues to evolve (because we must remember that exercise science is a really new field - probably only in its second generation of scientists), what will happen is that it will become more and more specialized - for example, you'll get a molecular biologist-exercise science specialist. And perhaps a sports science-physicist, who no longer makes that mistake, because they're equally able to talk physics as they are physiology. But that is probably the next generation.

In any event, back to the discussion, the 'threshold' to which exercise science refers is a 'deflection point' - this is a really clumsy term that has often been used instead of threshold, specifically because of the issues you brought up. Now, it too is a little clumsy, because depending on how you measure it (sampling frequency), you sometimes find an exponential growth in lactate levels, other times you get this "deflection". That is, if you sample the athlete's blood every few MINUTES, you miss out on the fact that it actually rises exponentially, so there is no deflection point!

So that theory is also fraught with problems! And it's so entrenched within the culture of sports science and among the scientists that it's just unbelievable how hostile they will become when challenged on it. But yes, we're in the same camp on this one - now we just have to figure out how to change the perception and, very very vitally, figure out how to APPLY the knowledge.

The reason, incidentally, that this kind of "threshold" theory becomes so ingrained among athletes, is because it's such a beautiful model for athletes to think about when they train. The concept that you can train at two distinct levels for two distinct benefits is so elegant and so easy to understand, that it's a winner concept. It's like in marketing, if you develop a product that meets the needs of the consumer, you never actually have to "sell it" - it sells itself. So they say that good marketing eliminates the need for selling!

Well, that is what happened with lactate theories - they were so powerful, and it's wonderful to believe, as an athlete, that you suddenly "switch on" lactate, that everyone was won over right away!

We're actually planning a series on this in the not too distant future, so do join us then!

Cheers
Ross