Running Economy
The energy cost of running at a given pace: how efficiently an athlete converts oxygen into forward motion. Essentially, running efficiency.
Running economy is the amount of oxygen an athlete uses to run at a given pace. Two runners moving at the exact same speed can have meaningfully different oxygen costs to sustain it, and the one who spends less oxygen for the same pace has the better running economy. It's essentially a measure of running efficiency: how much useful forward motion an athlete gets out of each breath.
Why it explains what VO2 max can't
VO2 max sets the ceiling on how much oxygen an athlete can take in and use. It doesn't say anything about how much of that oxygen a given pace actually costs. That gap is where running economy lives, and it's a big part of why two athletes with an identical VO2 max number can post very different race times. One of them reaches race pace using a smaller share of their aerobic ceiling, purely because their running form costs less oxygen per stride, and can hold that pace longer with less strain, even though a lab test would call the two of them physiologically equal.
This also explains why economy tends to matter more the longer and more trained a field gets. Among recreational runners, raw VO2 max differences often dominate the outcome on their own. Among well-trained athletes at a similar level, where those differences shrink, economy becomes one of the clearer things left to separate them.
What's actually known to improve it
Strength training has some of the better evidence behind it as a running-economy intervention. A 2022 systematic review and meta-analysis of controlled studies found that heavy resistance training, work done at loads close to an athlete's maximum, improved running economy and running time-trial performance in distance runners, with a clearer effect than plyometric training used on its own. Programs running around three months showed more consistent gains than shorter ones, which points to economy being a slow adaptation, not something a few weeks of gym work produces. See strength training for triathletes for how that fits around a full training week.
Running-specific technique work has supporting evidence too: periodized, running-specific strength training has been shown to help competitive runners hold their stride length under fatigue better than runners without it, a plausible part of the mechanism, since form that holds up late in a race costs less oxygen than form that's breaking down.
General training volume plays a smaller, more indirect role. More years of running and consistent mileage tend to nudge economy in the right direction, mostly because an experienced runner's mechanics settle into a more efficient pattern. But volume alone is a slower, less reliable lever than strength training or deliberate technique work, and it isn't something an athlete also training to swim and bike can increase indefinitely.
None of this means running economy can be trained overnight, or that a specific percentage improvement is guaranteed for any given athlete. What the evidence does support is that it's a trainable quality, not a fixed trait set entirely by genetics or footstrike pattern, and that strength training is one of the more reliable ways to move it.