Running economy
Evidence: strong
The energy cost of running, and what separates runners of similar VO₂max. Best improved by strength work and shoes, not by chasing a “perfect” form.
Running economy is the energy cost of running at a given submaximal speed. A runner who uses less energy to hold a pace is more economical (Conley & Krahenbuhl 1980; Saunders et al. 2004). It is the determinant that most often explains performance differences between runners whose VO₂max values are similar. In a homogeneous group of high-VO₂max runners, economy related to 10 km time at about r = 0.82 and varied by roughly 30% between individuals (Conley & Krahenbuhl 1980).
A determinant, not the whole story
Good economy alone does not make a fast runner. It is one of three determinants, and performance comes from training all of them together, not from optimising any single one. An economical runner still needs the aerobic engine (VO₂max) and the trained ability to sustain a high fraction of it.
How it is measured
Economy is measured as the steady-state cost of running at a fixed submaximal speed, using a metabolic cart to analyse expired air during several minutes of running, once oxygen uptake has stabilised. The result can be expressed as an oxygen cost or as an energy cost, and the distinction matters:
- Oxygen cost, in millilitres of oxygen per kilogram per kilometre. Simple, but incomplete, because the same volume of oxygen yields different amounts of energy depending on whether fat or carbohydrate is being burned.
- Energy cost, in kilocalories or joules per kilogram per kilometre, derived by combining oxygen uptake with the respiratory exchange ratio to account for the fuel mix. This is the better measure, because two runners using identical oxygen can differ in true energy cost if their substrate use differs (Fletcher, Esau & MacIntosh 2009). Typical energy cost is around 1.0 to 1.1 kcal/kg/km.
Economy must be measured at a standardised, genuinely submaximal speed and in a fed, rested state, because fuel status and fatigue shift it. It also does not compare cleanly across laboratories or across speeds, since protocols, treadmill calibration and the chosen speed all change the number. As with VO₂max, it is most trustworthy as a within-runner change over time under fixed conditions.
What determines it
Economy is multifactorial, combining anatomy, biomechanics and metabolism:
- Elastic energy return. The largest modifiable lever. A stiffer Achilles tendon stores and returns more elastic energy per stride and is associated with better economy (Achilles stiffness and economy). Leg and tendon stiffness, and the timing of muscle activation around footstrike, govern how much of each stride is “free”.
- Ground contact time and leg stiffness. These relate to metabolic cost in a curved fashion, and most trained runners already self-select values within about 5% of their own optimum (ground-contact and leg-stiffness optimisation study). This tempers the popular idea that consciously changing form will easily improve economy: gait is largely self-optimised, so deliberate cueing often costs more than it saves.
- Anthropometry and biomechanics. Limb mass distribution, foot and tendon structure, and stride mechanics all contribute, mostly not trainable.
- Metabolic efficiency and fibre type. Mitochondrial efficiency and a higher proportion of slow-twitch fibres lower the cost of force production.
- Footwear. External, but large: carbon-plated super-shoes improved economy by about 4% on average in the original study of a prototype against 2017 racing flats, through the interaction of compliant foam, geometry and a stiff plate. The figure is comparator-specific and varies widely between runners, from a hindrance to a benefit, rather than being a fixed property of the shoe (individual variation).
The integrated model
Joyner combined the three determinants into a single framework: achievable marathon velocity is set by VO₂max, multiplied by the fraction of it sustainable at lactate threshold, divided by the energy cost of running (Joyner 1991). The model anticipated a sub-two-hour marathon decades before it was approached, and remains the clearest way to see how the three combine: improving any one, while holding the others, makes a runner faster.
What improves it
- Strength training. The best-evidenced training lever, improving economy by roughly 2 to 8% with larger effects at faster speeds, through stiffer tendons and better neuromuscular efficiency rather than added mass (Blagrove et al. 2018; Llanos-Lagos et al. 2024). Heavy resistance has a slightly larger effect than plyometrics (Eihara et al. 2022).
- High mileage over time. Years of training gradually improve economy, though the effect is slow and hard to isolate from selection.
- Super-shoes, as above, the largest single acute improvement available, but external to the runner.
The honest caveat: because gait is already near-optimised, economy is one of the harder determinants to move deliberately, and most of the reliable gains come from strength work and from the right shoes, not from chasing a “perfect” form.