Running Economy

Mapping the determinants.


In essence, endurance performance comes down to three things:

  • How big your engine is (VO2max, peak velocity, or any other measure of maximal capacity)
  • How much of that engine you can use (i.e. the fraction of the above that can be sustained)
  • How efficient that engine is (i.e. how well you can translate metabolic energy to movement)

The interplay between the three ultimately determines performance6,10. Having a big engine is useless if you’ve got a flat tyre, and that’s where an understanding of economy* comes in.

*Note that economy refers specifically to the oxygen cost of running, rather than the energy cost per se. I use the term “economy” as I expect it to be more familiar to most readers, but strictly speaking this is a discussion of energy cost.

Running economy is one of the more nebulous aspects of our physiology. It promises perhaps the greatest silver bullet in endurance sport9 yet seems so frustratingly impervious to our efforts to both understand it and affect it.

The research literature with regards to running economy is vast and fragmented. There are studies investigating the effects of training transversely and longitudinally, studies exploring differences between walking and running, studies looking at developing footwear, and studies comparing different species, to name just a few. Hence, synthesising the information of all these studies is no mean feat, and that’s exactly what a recent review by Jean-Rene Lacour and Muriel Bourdin11 did. While I would advise anyone with an interest to read it, I thought converting it into a diagram might help it reach a wider audience. To view it click the image below.

an infographic on the physiological and biomechanical determinants of running economy

Of course, this is nowhere near as comprehensive as the original review, and some sections have been omitted for brevity (e.g. effects of growth & maturation, ageing, ethnicity etc). However, what I hope it does provide is a starting point, and a reference “map” when reading any related research.

Two points to highlight:

The effect of body mass:

When the cost of running is expressed relative to body mass (i.e. J/kg/m) it appears that body mass and running cost are inversely related - that is, increasing body mass reduces running cost4. Why that should be so is probably related to elastic energy storage from the increased force, but note this is more a theoretical exercise than a practical one. Regardless of the aforementioned, if a running race is considered in units of work (e.g. 4.2 kJ per kg per km) then a lower body mass means less work for a given distance. In turn, if the sustainable rate of energy expenditure for that race is constant, less body mass means a faster finishing time. However, if you were to wear a weight vest and measure your running cost in terms of J/kg/m, you would be more economical with the weight vest.

The effect of footstrike:

As the diagram shows (non-exhaustively I might add) there are many aspects to an individual’s running gait, and they almost all interact. When the effects of footstrike per se are isolated — that is, controlling for step frequency, shoe mass and all other variables to the best of our ability — the differences become trivial15. It is often cited in this respect that forefoot strikers are better able to store energy in the elastic structures of the leg. However, it should be borne in mind that elastic energy storage — i.e. controlled lengthening contraction — is energetically costly in itself, so any net benefit of energy recovery may be little to none.

Finally, there is one point missing from the diagram, and that’s because it could only justifiably be included by having it engulf everything else. That point is individual variability. While there are certainly factors the seem to dictate running economy at the population level, predicting any one individual’s running economy on these bases may be futile.


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