Running Economy Explained: Why Two Runners With the Same VO2max Race Differently

Two runners can post the identical VO2max on a lab test and still finish a 10K four minutes apart. Ask a coach why, and the answer is usually running economy — how much oxygen your body burns to hold a given pace. It gets far less attention than VO2max, but among runners with similar aerobic capacity, it's often the number that actually decides who's faster.

What running economy actually measures

Running economy is the amount of oxygen your body consumes to sustain a specific pace, usually expressed in millilitres of oxygen per kilogram of bodyweight per kilometre (ml/kg/km), or sometimes per minute at a fixed treadmill speed (ml/kg/min at, say, 12 km/h). Lower is better — it means you're covering the same ground on less fuel.

Think of it as fuel efficiency for a car. Two cars can have identically sized engines (VO2max) and still get very different mileage per litre, because one wastes less energy to friction, weight, and drag. Running economy is the same idea applied to a body: how much of the oxygen you're capable of using actually turns into forward motion, versus how much is lost to inefficient mechanics, wasted vertical bounce, or muscles working against each other instead of together.

A runner using 200 ml/kg/km at a given pace, compared with another using 230 ml/kg/km at the identical pace, is spending roughly 13% less oxygen to do the same job. At a shared VO2max, that gap converts almost directly into being able to hold the pace longer, or hold a faster pace for the same effort.

Why equal VO2max doesn't mean equal race times

This is where running economy stops being a lab curiosity and starts explaining real results. A well-known 1980 study by Conley and Krahenbuhl measured a group of elite male distance runners with similar VO2max values and found that running economy alone explained roughly 65% of the variation in their 10K race performance — VO2max barely separated them at all. The fastest runners in the group weren't fitter by the lab test; they were simply cheaper to run.

What is VO2max sets the ceiling on how much oxygen you can use at maximum effort. Running economy determines how much of that ceiling you actually need to spend at any given pace. A runner with a VO2max of 55 ml/kg/min and excellent economy might race a half marathon at a lower percentage of their max than a runner with a VO2max of 60 who has to work harder, mechanically, to hold the same pace. On race day, the runner spending less of their ceiling has more left in reserve — and usually the better finishing time.

It's also why some racers with unremarkable lab numbers consistently outperform runners who test better on a treadmill. Economy doesn't show up on a VO2max test, but it shows up on the clock.

What actually improves running economy

Running economy responds to training, and the evidence points to a specific handful of approaches — not a general "run more and hope."

Strides. Short, relaxed accelerations of 15–20 seconds, building smoothly to close to top speed and easing back down, run a handful of times after an easy run. They train your neuromuscular system to fire more efficiently and sharpen stride mechanics without the fatigue cost of a hard workout. Strides are one of the lowest-effort, highest-return additions missing from most easy-running plans.

Hill sprints. Short, steep efforts of 8–12 seconds at a hard effort — not long hill repeats — recruit fast-twitch fibres and build the kind of power that translates into a stiffer, more elastic push-off on flat ground. Because the incline caps your speed, hill sprints load the muscles hard without the joint-impact cost of an equivalent flat-ground sprint.

Heavy strength training. A frequently cited 2008 study by Støren and colleagues had trained distance runners add eight weeks of maximal-strength training — half squats at 85–90% of one-rep max, four sets of four reps, three sessions a week — without changing their running volume, and measured a roughly 5% improvement in running economy alongside better time-to-exhaustion. The mechanism isn't added muscle bulk; it's a stiffer, more elastic musculotendinous system that returns more energy on each ground contact instead of absorbing it.

High mileage, sustained over years. Economy improves gradually with accumulated easy running, likely through better neuromuscular coordination, more efficient fat use at a given pace, and connective tissue adapting to repeated load. This is a slow, multi-year process rather than something a single training block delivers — part of why experienced runners with modest VO2max numbers often still race well.

What doesn't move the needle

Chasing extreme flexibility. Research from the 1990s by Craib and colleagues found that runners with less flexible hips and ankles tended to have better running economy, not worse. A moderately stiff tendon stores and returns elastic energy more effectively than a very loose one. Some flexibility supports healthy range of motion, but stretching for maximum flexibility isn't an economy intervention, and overdoing it can work against you.

Forcing a specific footstrike. Coaches and shoe brands have both pushed forefoot striking as an economy fix at various points. The evidence doesn't back a universal prescription — studies comparing footstrike patterns at matched paces generally find no consistent economy advantage either way, and switching an established heel-striker to forefoot striking often makes economy briefly worse while the calf and Achilles adapt to the new load. Footstrike is largely a byproduct of pace and individual mechanics, not a lever to pull on its own.

Cadence changes on their own. As covered in why cadence isn't a number to chase, nudging cadence up or down without an underlying reason doesn't reliably improve economy — it's a targeted tool for specific overstriding-related issues, not a general economy fix.

One-off sessions without volume behind them. A single week of strides or hill sprints won't move the number. The studies showing real gains used weeks of consistent exposure — economy adapts slowly, similar to strength or aerobic capacity, not inside a single session.

How running economy shows up in race predictions

Running economy is baked invisibly into every performance-based prediction, including the race time predictor. Tools like it extrapolate a goal time from a recent result using an assumed relationship between distance and pace, and that relationship holds only as well as your economy stays consistent across the gap. If you've spent two months adding strides, hill sprints, and heavy strength work on top of your usual mileage, a 5K time from before that block will understate what you can now hold at 10K or half-marathon distance — because your economy, not just your VO2max, has moved.

It also explains why your training pace zones, built from a threshold pace, sometimes feel like they've loosened up even before your race times have caught up. Economy improvements often show up first as a given pace feeling lighter, weeks before they translate into a faster time trial or race result — so if threshold pace suddenly feels comfortable, it's worth re-testing rather than assuming the zones are stale.

Worked example: what a 5% economy gain is worth

Take a runner holding 4:30/km at a steady sub-maximal effort, with a running economy around 210 ml/kg/km. After eight weeks of twice-weekly strides, once-weekly hill sprints, and a simple heavy-squat routine layered onto their usual mileage, their economy improves by a realistic 5%, to roughly 200 ml/kg/km — the same range Støren's runners saw.

That 5% oxygen saving at the same pace means the effort that used to cost, say, 85% of their threshold intensity now costs closer to 81%. Practically, that shows up as either holding 4:30/km more comfortably for longer, or nudging the same effort level to a slightly faster pace — commonly a 5–15 second per km improvement at race effort, which compounds into minutes over a 10K or half marathon.

None of that shows up on a VO2max test. It shows up as training feeling easier at the same pace, and eventually as a faster number on the clock — which is exactly why running economy, not just aerobic capacity, is worth training on purpose.