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Tuesday, December 11, 2007

Running Economy Part II

The Biomechanics of Running Economy

Today sees Part II of our series on Running Economy. After spending the first two posts introducing the concepts and discussing the results from the Zersenay Tadese study, today we move onto some fundamental concepts of running economy - the physiology and biomechanics of running economy explained (partly, we hope!)

I say "fundamental" with some caution, because the more one digs into this particular topic, the more you realise that the science, and our knowledge of how to put running economy into practice, is still a long way off where it should be. I know that our good friend Amby Burfoot is fond of reminding us that science is actually a long way from understanding running physiology, and he's quite right. In the words of Sir Roger Banister, the first man to crack the 4-minute mile and who then went on to become a respected neurologist:

"The human body is centuries in advance of the physiologist, and can perform an integration of heart, lungs and muscles which is too complex for the scientist to analyse"
Running economy is one such 'integration". And with that in mind, let's get to it!

A fundamental paradigm - running economy: one of many explanations?

The first point that I have to make is that we should be careful not to over-emphasize the importance of running economy to performance. Yes, it is important. And yes, any coach, scientist or runner who is dedicated to training and improving performance needs to be aware of running economy and possible means to improve it. And yes, it has been relatively "forgotten" by science in recent times, hence our relatively limited understanding of it. But regular readers of The Science of Sport will also know that we're not particular fond of "magic potion", "silver bullet" training methods or science principles! So we must approach running economy for what it is - one of many explanations for performance.

So when we look at the East Africans, we note that they have a better running economy than the European runners. We also note that the best runners tend to be the most economical, that certain physiological characteristics predispose runners to be more economical, and that certain types of training improve running economy more than others (more on that in our next post, by the way). This is only partly relevant to you as you read this, because ultimately, you must not "lose sight of the wood for the trees", and become so stuck in the running economy analysis that you forget to worry about performance! And let running economy take care of itself...

Factors influencing running economy

Running economy, to repeat, is an integration of numerous systems and characteristics, biomechanical, and physiological factors. It would take a month of articles to cover all of them in detail, so we'll skim the list quite substantially, and discuss these three categories very broadly.

Biomechanical factors influencing running economy

The Zersenay Tadese article attributed his incredible running economy to the small size (and thus lighter weight) of his calves, compared to the European athletes. That is, he is carrying less weight at the extremities than they were, since his calf circumference was a good deal smaller than the Spanish runners he was compared to.

I suspect that this is only part of the answer, and possibly a very small part. As mentioned in Part I, Tadese's economy is much lower than the Kenyan runners tested before him, who probably do not have quite as much of a disadvantage as far as the calf muscle goes. So while the difference between Tadese and the Spanish might be calf-size related, there is more to it than just this.

According to an excellent review article from 2004 (by Saunders, published in Sports Medicine, 2004), the following biomechnical factors are important for running economy:

  • Height: Slightly smaller than average is better for men, while slightly taller is better for women - I must confess that I don't have an explanation for the difference!
  • Somatotype: Ectomorphic physique demonstrates best running economy. An ectomorph is generally long-limbed, thin, has shoulders that are about the same width as the hips! Think Paul Tergat, or just about any Kenyan long distance runner!
  • Body fat: Low percentage, because body fat represents additional weight that must be carried, increasing the oxygen cost of running
  • Leg morphology: Most of the weight distributed closer to the hips. In other words, if you have mass, carry it in the quads and not the calves! This agrees with the suggested reasons for Tadese's economy
  • Pelvis: Narrow
  • Feet: Smaller than average
  • Shoes: Lightweight but well cushioned. There is evidence that cushioning improves running economy, possibly because it reduces the work required by the muscle to absorb and cushion the landing (that's the theory, anyway)
  • Stride length: Freely chosen. This is interesting, because there is evidence from research that if you chop your stride to try to increase the cadence, your running economy worsens. We touched on this in our series on Pose running recently, and a lot of people find that they chop their stride when trying to use the method. According to the economy research, this would be undesirable. Having said that, if you are overstriding, then it's just as bad, if not worse, because a great deal of energy is lost in braking. This factor, perhaps more than any other, emphasizes that "Practice makes Perfect" and that running is a skill which must be practiced and learned. It happens naturally, yes, but it must be learned.
  • Kinematics: A few things here - first of all, low vertical oscillation of the centre of mass. What does this mean? Well, it means don't waste time going up and down if you don't need to. The less you waste on vertical braking forces, the better. It was always rumoured that the most economical runners were effectively "rolling" their legs along beneath their hips - this is in fact a premise of Pose Running, as we discussed once before. There is nothing new to this at all (despite the fact that it was packaged as 'revolutionary', because we've known for a long time that a relatively flat trajectory is more economical.
  • Secondly, minimal possible movement of the arms. That's not to say zero movement, because the arms play an important role in providing some rotational stability, but the movement must not be excessive. On this note, you see some absolutely bizarre arms carries among the elite runners, which you'd have thought would be corrected, but that only re-inforces that this is not an exact science.
  • Third, a more acute knee angle during the swing phase. In other words, when your trail leg is coming through (eg. your right foot is planted on the ground and your left leg is catching up), then it's better to have that knee fully bent than straight. The reason for this is physics, relating to rotational torque and the force that is required of the muscles to bring the leg through. But the practical point is that the hamstrings come into play to reduce running economy, because they contribute to the flexing of the knee. One practical issue here is that when running slowly, it's almost impossible to bend the knee more than a few degrees - you'd be working so hard to bend your knee, the effect would be increasing your cost, not reducing it! So this is largely influenced by running speed.
Then there are a couple of other factors, which we'll touch on as we develop our discussions further in the next few posts.

But what is important to take out of the above list is that if you are a tall, skinny man, weighing next to nothing, with hips as wide as your shoulders, short arms, no body fat, and you wear a well-cushioned pair of size 6 shoes, you might have a good running economy!

The most important thing that jumps out from the above list is that there are some factors that one is born with (narrow pelvis, foot size, height, distribution of weight on the legs) and others that are improved with training and preparation, such as the kinematics like vertical oscillation and arm carry. Point is, great runners are born, and then trained. But everyone can run, and so as you read this, there is probably a great deal that you can do to improve your running economy, which would then translate into improved performance. But we'll discuss that in a separate post, later in the week.

Join us then!


Anonymous said...

Thanks for another interesting addition to the running economy debate/review.

I have to confess that like most physiologists I haven't really given running economy as much attention as maybe it is due, partly because of time (get the basics right before trying to tweak little aspects) and partly because a limited exploration into the area shows that as scientists we don't really know that much about it and therefore I struggle to educate coaches with any great authority. However, I am fully aware that that doesn't mean it is unimportant - far from it.

Here in the UK coaches/physiologists do talk about running economy quite a lot, however I’m not entirely sure they always know exactly what they are talking about. I often here coaches saying that increasing volume or S & C will help improve your economy. It’s even written into the Physiological Support Guidelines that UK Athletics gives out that ‘generally most economical runners tend to be older and to cover higher mileage…..accumulation maybe important……running economy will tend to improve over time and should be monitored’. In my limited experience (with 800-5000m runners) I see athletes with good economy (180ml/km is the best in a 3:38 1500m runner) or poor economy (210ml/km in a 1:45 800m runner) but I see little changes in economy over time. I’ve seen athletes come off the back of a period of very little training and have identical economy to when they were covering 80miles plus a week. I’ve also seen athletes start to incorporate focused S & C work and greatly improve leg strength, change stride length and speed (time) but economy stays the very similar. Obviously there has to be some element of ‘proper practise’ to improve and simple doing the same thing again and again is probably not beneficial.

With regards to the research conclusion that it is down to smaller calf, I am like you a little unsure. A quick review of the data I have shows no strong correlation either between different athlete’s calf size and running economy or within an individual athlete as their calf size has increased or decreased.

In response to your reply to my earlier comment with regards to Tadese super low economy coupled with high VO2max it is indeed an interesting conundrum of why he can’t run faster. Perhaps what is happening to other people at 80%VO2max is happening to him at 60%? I still haven’t read the original article (Athens password is playing up) but maybe he is going through LT1 (I know more than a few problems with that as well) at a much lower % VO2 than other marathoners, or perhaps his substrate use is very different? (These are more uneducated guesses than anything – before anyone get on a high horse!)

One last comment. As a general I do tend to see athletes economies change at different speeds. As makes sense the speed at which they complete their ‘easy’ runs they tend to be most economical and as speeds increase they tend to become less economical. Another glance at our data also suggests that it is only the athletes with the poorer economies that increase like this. The athletes with economy below 190ml/km tend to remain consistent at that rather than increase.

Sorry for the long post!

Ross Tucker and Jonathan Dugas said...

Hey Running Physiologist

Thanks for the post, and don't worry about the length. You've shared some really great insights into the athletes you've worked with.

I agree with fully that the information that is available on running economies in the "lay" media is often slightly compromised by retellings! It's like the physiological equivalent of "broken telephone" and I suspect that a lot of misinformation exists because original research is taken progressively further and further away from its context.

But the talk of S & C and higher mileage does have some basis, and we'll do our best in the next post to discuss those aspects. Flexibility is another one that is particularly interesting with regards to its effects on economy.

I myself am a huge believer in the role of the brain during exercise, and with regards to running economy, this refers to the role of the CNS in the regulation of the stiffness and resultant release of energy from the tendons during the running gait. I think that this is a critical, and as yet unmeasured factor (though it is known to be important). And so I really do believe that training the nervous system is the key to improving running performance, and will have a large effect on running economy.

I'll try to get at that in the next post - I tried to broach the subject in this post, but it got a bit clumsy, so saving it for another day!

One last thing - it's incredibly rare to have high economy and high VO2max. In cyclists, were efficiency (as opposed to economy) is measurable, there is an inverse relationship between VO2 max and efficiency, which suggests that the guy with the least efficient pedal stroke has the higher VO2max. The same probably applies to running and so for Tadese, the problem is that both his are high, and that's what arouses my curiosity!

To be that efficient and to reach a VO2max of 83 is extraordinary. In fact, if his economy was 180ml/kg/km at his peak running speeds, then you could work out that his peak speed would be 2:10/km! So it's just not possible, unless he is incredibly inefficient and uneconomical as speed goes up. This is definitely one to explore at some stage!

Thanks again!

Iker said...

I suppose all those measurements have been made in a lab, where no air resistance exists. However, 4min/km is 15km/h, 3min/km is 20km/h and 2min/km is 30km/h. Air resistance grows with speed at a rate 'steeper' than quadratic (with the square of the speed) and it happens to start to dominate the power requirements at around 25km/h (unless you are running uphill!). So, in the field, such huge differences in oxygen requirements would lead to smaller differences than those suggested in this post. And this guy seems to be beating every record, so the difference is there, it's just not as huge as you suggest it should be if the 150 result was true!

This argument could be related to the idea of the running economy being reduced fast with speed. It may not be so in the lab, but it is in the field, simply because at the speeds we are talking about air resistance kicks in!

It would be very interesting to see if this guy can run a 2:18/km marathon in the lab (as he obviously cannot in the normal way).

Congratulations and thank you for your awesome blog, which I discovered by chance and enjoy so much. Very serious stuff in a very easy to take way.

Anonymous said...

Great subject to tackle -- thanks guys!

I know you've said that running economy is measured as the cost of running one kilometre, which maybe explains why this discussion seems to be focused on middle/long distance runners, but I can't help wondering whether sprinters -- or more specifically the 200 and 400 metre runners -- would actually demonstrate superior running economy.
Or am I falling into the economy/efficiency definition trap?


Anonymous said...

Does running economy have a +ve or -ve correlation with VO2max? What does it imply?

Thanks for your prompt response.

Anonymous said...

In the article, you say:

But what is important to take out of the above list is that if you are a tall, skinny man, weighing next to nothing, with hips as wide as your shoulders, short arms, no body fat, and you wear a well-cushioned pair of size 6 shoes, you might have a good running economy!

I assume you meant "a slightly short man", right?

Ross Tucker and Jonathan Dugas said...

Hi everyone

Apologies for the delay in getting back to you all, been busy the last few days.

First of all, Stan, you're quite right, it should read that "Shorter" runners are advantaged. The evidence is that taller women are more economical, but shorter men. I have no reason why this might be, but I suspect they have not tested enough women, and perhaps not the right women, to be able to say this definitively!

But I was typing that, and in my mind, I had visions of a very ectomorphic Paul Tergat, and so that's why I typed "taller". Apologies, and well spotted! I've changed it in the post, so anyone who reads it from now on will get the right story! Thanks!

Then to half-timer, generally (because there are always exceptions to the rule), people who have a good running economy have a LOW VO2MAX. The relationship is thus inverse. This has been demonstrated in cyclists as well, by the scientist Lucia, where he showed that the guys who had the lowest VO2 Max values also were the most effcient.

Same goes for running - more economical runners tend to have lower VO2 max values. This is in itself quite interesting because there is a "chicken-egg" debate around whether the low VO2 max is the cause or the result of the economy.

To me, it's pretty clear that the more economical you are, the lower your VO2max would be across the whole range of workloads - of course, you might find relative changes where you get less or more economical as workrate rises, but generally, you find this pattern. This is because the VO2max is a function of the work rate, and so an economical runner, who uses less O2 at lower intensities, will also be lower at high intensities, and simply cannot get to high enough intensities to lift VO2max higher.

What limits exercise then? Well, that's the million dollar question and I brought it up in the Post on the Tadese study. We'll have a good look at that in the future, probably a series of posts in 2008!

And then finally, the question about sprinters is a good one. The evidence would suggest that sprinters are LESS economical - there is evidence that a higher percentage of slow twitch muscle means improved economy.

Also, high volume training improves economy - neither of these are typical of a sprinter!

Having said all this, sprinters also do a great deal more plyometric training and strength work, and both of these are linked to better economy. And then of course, economy is highly unlikely to have any impact on sprinting performance - the prudent use of oxygen is not really vital to a sprinter. And so I don't think that many have even looked at this variable in sprinters.

If pushed to guess, I would say that at all running speeds below sprinting, a long distance runner will be more economical. But the plyometrics, the strength work and explosive work done by sprinters means that at the supra-maximal speeds, sprinters have the edge. But I don't think that this will ever be measurable as "economy", but rather efficiency. So you're not confused at all - fair question, but again, no definite answer.


Ron George said...

A good runner will probably have an optimum amount of vertical oscillation. This is learned neuromuscular. Going too low and too high probably wont help.

Too high because you're unnecessarily wasting your energy. Too low, probably because, as you say in Part 3, time on ground might actually increase.

The legs need a certain amount of energy to support the body weight and "bounce"" it to the next step.

Ross Tucker and Jonathan Dugas said...

Hi Ron

Yes, absolutely, agreed 100%. The other problem with trying to reduce the vertical oscillation too much is that you compromise stride length eventually, which affects speed substantially.

But you're quite right - learned neuromuscular is the way forward!


Anonymous said...

I am a small female (160cm) with a 31 inch inside leg. I find it frustrating and hard to understand when I am running that I see people overtaking me who are by my judgment running "slower" than me because their steps are less frequent. This even happens with people who aren't taller than me. I aim to keep my stride length reasonably long without over stretching and am quite flexible and try to get some power when I push off so I don;t understand what the problem is

Unknown said...

I wanted to email this to you, but I couldn't find an emailadress.
I thought this would be interesting for you considering this topic. Melanie Scholz claims that people who have shorter heels can run faster because of better energy-storage economy.


Ron Wolf said...

Fab list of factors, not sure how I had missed this article? I think there are two factors missing tho.

One is foot angle (mostly at foot plant). I don't know for sure that its a factor, but someone who runs with a straight foot looks (for whatever that's worth) more efficient than someone who runs with their foot splayed out. Seems that the stride is naturally longer in the case of a straight foot and that there is more spring to the step. But maybe its just looks...

The other is hip swing. A few inches per stride can be gained by extending the leg movement up into the top of the hip. Right, stride length is not the same as efficiency. Still...

I nothing objective to contribute here, just what seems to make sense. Maybe, by now, these factors have been considered by some study or other.

And then what about arm length, angle, timing?