Running Economy Part II  //  The Biomechanics of Running Economy

11 Dec 2007 Posted by

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…

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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!
Ross