The oxygen cost of every stride
Running economy is the energy cost of holding a given submaximal speed. Two runners with the same VO2max can still finish far apart if one uses less oxygen at race pace, and that gap reaches about 30% among trained runners with similar aerobic power in the literature. Economy sits alongside VO2max and the fraction of it you can sustain as a main lever of distance performance, especially once VO2max values cluster tightly.
Before the detail, the bigger picture. For nearly all runners, the gains that matter most still come from running more, consistently, over months and years. Economy research is useful as a map of second-order levers on top of that volume. The sections below cover how economy is measured, what seems to determine it, and which interventions have decent evidence behind them.
Key takeaways
Running economy is usually reported as submaximal oxygen uptake at a fixed speed (ml·kg⁻¹·min⁻¹) or as oxygen cost per kilometre (ml·kg⁻¹·km⁻¹). Laboratory values underestimate outdoor cost unless air resistance is accounted for.
Well-controlled studies put day-to-day typical error around 1.3–5%, and a smallest worthwhile change near 2.2–2.6% at common test speeds in highly trained runners.
Economy reflects metabolic, cardiorespiratory, biomechanical and neuromuscular factors together. A change that helps one runner can leave another unchanged.
Endurance training history and training volume are the traditional routes to better economy. Heavy, explosive and plyometric strength work often improves it by roughly 2–8% in controlled studies; altitude exposure and footwear mass or cushioning also shift cost in measurable ways.
There is no universal "efficient" gait to copy. Self-selected stride length is usually close to optimal, and forefoot striking is not inherently cheaper than rearfoot striking.
How running economy is measured
The standard lab approach is steady treadmill running below the lactate or ventilatory threshold for long enough to reach a stable VO2, typically a few minutes at each speed. Common reference speeds run from about 12 to 21 km·h⁻¹, with 16 km·h⁻¹ used often for comparisons. Some labs express economy as caloric unit cost so that substrate use is reflected, not only oxygen uptake.
Reliability is good enough for training decisions when the protocol is controlled. Footwear, time of day, prior training, nutrition, the analyser and the room all affect repeat measures. Saunders and colleagues put a smallest worthwhile change near 2.2–2.6% at 14–18 km·h⁻¹ in highly trained distance runners.
Treadmill numbers transfer imperfectly outdoors. Air resistance rises with speed, and treadmill and road muscle actions differ. A roughly 1% treadmill incline is sometimes used to approximate outdoor cost. Portable systems can measure overground running, with weather and terrain then in the result.
What determines it
Barnes and Kilding's 2015 open-access review in Sports Medicine - Open frames economy as the sum of metabolic, cardiorespiratory, biomechanical and neuromuscular efficiency. Heritability is described as the prevailing background factor, with limited genotype work so far. Many of the remaining pieces respond to training.
On the metabolic and cardiorespiratory side, lower heart rate and ventilation at a given speed associate with better economy across large samples of habitual runners. Ventilation changes in particular have tracked economy improvements after intensified training in recreational runners, and the oxygen cost of breathing can explain a meaningful slice of that shift. Core temperature effects are mixed across studies. Muscle fibre composition matters in principle, because type II fibres cost more ATP per unit force than type I, though findings linking fibre type to economy are mixed.
Biomechanically, mass farther from the torso raises cost more than the same mass on the trunk, which is why shoe mass shows up clearly. Shorter Achilles tendon moment arms and somewhat less flexible lower-limb joints have been linked with better economy in small samples. Runners usually settle near their most economical stride length; forcing large changes from that length raises VO2. Vertical oscillation, joint angles and ground-reaction patterns show only modest, often individual-specific associations. Habitual forefoot and rearfoot strikers can show similar economy; switching a habitual rearfoot runner onto a forefoot pattern has raised oxygen cost in experiments.
Neuromuscular factors close the loop. Greater leg stiffness, sharper pre-activation before ground contact, and better use of the stretch-shortening cycle all relate to lower cost. Elastic energy in the Achilles tendon and the arch of the foot is a large free contribution at typical speeds. Continued run training itself seems to tidy motor patterns: recreational runners show more variable recruitment than runners with years of high weekly volume.
What the evidence says improves it
Training volume and hard running
Improvements in economy have traditionally come through endurance training. Training history and training volume are repeatedly named as important, and uphill or level high-intensity interval work is often prescribed as a further stimulus. That sits neatly with this week's theme: the running you accumulate is itself one of the evidenced levers on economy, before any specialised add-on.
Generic weekly mileage bands from textbooks are a starting point at best. kaizen is hyper-personalised: it uses the overall intensity of the running you actually do, from pace and elevation, to set your training target for the week and recalculates as you run. The volume that improves economy is the volume you absorb, not a table average.
Strength and plyometrics
This section stays short because yesterday's post covers the strength evidence in full. In Blagrove, Howatson and Hayes's 2018 Sports Medicine systematic review of 24 controlled studies in middle- and long-distance runners, 14 of 20 studies that measured running economy found significant improvements of about 2–8% at one or more speeds after heavy, explosive or plyometric work, with six finding no change. Body mass and composition were essentially unchanged. Typical positive programmes used two or three sessions a week for at least six weeks, built around multi-joint free-weight lifts and plyometrics with short ground contacts. See Strength training for marathon runners: the evidence for dose, type and timing detail.
Barnes and Kilding's companion strategies review reaches the same broad conclusion: short-term resistance and plyometric training can enhance economy, most likely through neuromuscular changes such as stiffness and motor-unit recruitment rather than through large shifts in VO2max.
Altitude
Altitude acclimatisation produces central and peripheral adaptations that improve oxygen delivery and utilisation. Several studies in elite or well-trained runners report improved economy after live-high or simulated moderate-altitude exposures of a few weeks, though results are not uniform. For most recreational marathoners this remains an optional refinement when travel or a hypoxic setup is realistic.
Footwear, without the brand noise
Footwear changes economy through mass, cushioning and geometry. Classic loading studies show that mass at the foot raises aerobic demand far more than the same mass on the trunk, around 1% per 100 g at the shoe versus about 0.1% on the trunk. Better cushioning of similar mass has cut treadmill oxygen demand by a few percent in older ergonomics work. Lighter, adequately cushioned shoes tend to cost less oxygen than heavier, poorly cushioned ones at the same speed. Specific models sit outside what this post will name.
Stretching and flexibility
Stretching still belongs in an injury-prevention toolkit. For economy, the picture is that an optimal band of stiffness and flexibility seems to matter more than maximising range of motion. Several studies associate greater sit-and-reach flexibility with worse economy, and acute static stretching has mixed or neutral effects on cost. Chasing extreme flexibility for performance reasons is poorly supported.
What not to chase as a universal fix
No single kinematic cue defines efficient running for everyone. Dictating stride length for runners who already self-select near their optimum is usually wasted effort. Switching footstrike for economy alone is not supported when the runner is already habituated. Economy is individual enough that an intervention which helps one athlete can leave another flat.
Sources and how sure we can be
Definitions, measurement, determinants and normative framing come from the full open-access text of Barnes and Kilding (2015), Sports Medicine - Open. Intervention themes for endurance training, strength, altitude, stretching and nutrition are taken from the abstract and publicly summarised conclusions of Barnes and Kilding (2015), Sports Medicine ("Strategies to improve running economy"), cross-checked against Blagrove et al. (2018) for the strength numbers. Footwear mass and cushioning figures come from the biomechanics section of the 2015 open-access review and the ergonomics studies it cites. This post does not systematically cover trials published after those reviews. Laboratory economy still underestimates outdoor cost at speed, and many intervention samples are small or highly trained, so transfer to a recreational marathon build is an interpretation rather than a direct finding.
Economy sits on top of the kilometres
Training volume is itself one of the evidenced ways to improve running economy, which is why the other levers only make sense once the running is already consistent. For the vast majority of runners, building more durable weekly running over time remains the first-order work. Strength sessions, altitude blocks and shoe choices are second-order tools that can shave a little cost off each stride once that base is in place.
A fixed economy protocol, whether a strength template or a mileage ladder, still has to fit the running you have actually done. In kaizen the weekly target is set from that real intensity and updates as sessions land, so you can place the gym work, the easy volume and any sharper sessions where they leave you freshest.
See your fitness in kaizen
Chasing a cheaper stride takes months of steady work. kaizen calculates your fitness from your recent training and past races, then sets the weekly training target your goal requires. Pace and elevation define how hard each run counts, the target recalculates as the week unfolds, and you choose the sessions that fill it. Get kaizen on iOS or Android and see where your fitness stands.
