Running Economy: Understanding Efficiency Beyond VO2 Max

Take two runners. Give them identical VO2 max values — the same ceiling on how much oxygen their bodies can process per minute. Give them the same lactate threshold, the same fraction of that ceiling they can sustain for an hour.

By any reasonable model, they should race the same time. They frequently don’t. One of them is minutes faster over ten kilometres, and the difference is not in the engine.

It’s in what the engine has to pay.

The third variable

Endurance performance is usually described with two numbers. VO2 max: the size of the aerobic engine. Lactate threshold: the fraction of that engine you can run at without accumulating fatigue faster than you can clear it.

Both are real, both matter, and together they explain less than people assume. The missing term is running economy — how much oxygen you consume to run at a given speed.

Think of it as fuel consumption. Two cars with the same engine and the same fuel tank do not travel the same distance, because one of them is heavier, or shaped worse, or wastes energy in a thousand small ways. Running economy is the same idea applied to a body. It asks: at 4:30 per kilometre, how much oxygen does this particular runner burn?

The spread between runners is large. Two athletes with matched VO2 max can differ in economy by twenty per cent or more. Twenty per cent of your entire aerobic capacity is not a rounding error. It is the difference between a good runner and a very good one.

And it explains something that otherwise makes no sense: why VO2 max, tested in a lab, is a mediocre predictor of race performance among trained runners. Among untrained people it predicts reasonably well. Among people who all run seriously, it barely predicts at all — because they’ve converged on similar engines, and diverged on what those engines cost to operate.

What you’re paying for

Where does the oxygen go, if not into forward motion?

Some of it goes into vertical movement. Every centimetre you rise on each stride is work done against gravity that produces no horizontal progress. Over forty thousand strides in a marathon, small vertical excursions become an enormous energetic bill.

Some goes into braking. A foot that lands well ahead of the centre of mass applies a decelerating force. You then have to re-accelerate. You paid twice, and travelled the same distance.

Some goes into stabilisation. A pelvis that drops, a torso that rotates excessively, a knee that collapses inward — these are motions that muscles must resist. Resistance is work. Work is oxygen.

Some is recovered and reused, and this is the interesting part. Tendons — the Achilles above all — behave like springs. Landing stretches them, storing elastic energy. Push-off releases it. A stiffer, better-timed tendon returns more of that energy for free, meaning muscle contributes less, meaning less oxygen is consumed. A substantial fraction of the energy in each stride can be recycled this way, and how much varies enormously between individuals.

This is why economy is not a matter of “good form” in the aesthetic sense. It’s a matter of how much energy leaves the system versus how much comes back.

The problem with training it directly

Here is where economy becomes frustrating, and where most advice goes wrong.

You cannot practise being economical. There is no session called economy intervals. When runners attempt to improve economy by consciously changing how they run — landing differently, shortening their stride, adopting a form they read about — the results are inconsistent and frequently negative in the short term.

The reason is that your current running form is not arbitrary. It is a solution your nervous system converged on, over years and hundreds of thousands of strides, given your particular skeleton, your particular tendon stiffness, your particular strengths and restrictions. It is not necessarily the global optimum. But it is a local optimum, and it is optimised for the body you actually have.

Impose a different pattern from outside and you generally get less economy, not more, because you’ve forced a system away from its optimum without changing the constraints that put it there.

Which points to the actual answer.

Change the constraints, and the form follows

Economy improves reliably when the underlying properties of the system change. Not when the movement is coached from the outside.

Volume. The single most consistent finding. Runners with more accumulated years and more accumulated kilometres are more economical. Repetition is how the nervous system searches the space of possible movements and settles into cheaper ones. It is slow, unglamorous, and it works.

Strength. Heavy resistance training — genuinely heavy, low repetitions — improves running economy in trained runners, reliably, without adding meaningful muscle mass. The mechanism is largely neural and tendinous: stiffer tendons return more elastic energy, and stronger muscles operate at a lower fraction of their maximum, which is metabolically cheaper.

Plyometrics. Jumping, bounding, hopping. These train the stretch-shortening cycle directly — the storage-and-return mechanism that determines how much of each stride is free. Among the interventions studied, plyometric training produces some of the largest economy improvements per hour invested.

Fast running. Strides. Short hill sprints. Brief efforts at speeds well above race pace, short enough that they cost nothing metabolically. These recruit high-threshold motor units and improve the coordination of forceful, rapid contractions. Six twenty-second strides at the end of an easy run is not a workout. It is economy training.

Notice what these have in common. None involves thinking about your form. All of them change what the body can do, and then allow the nervous system to find its own way to a cheaper solution.

The uncomfortable part

Economy is also, to a real degree, given rather than made.

Tendon length and insertion points, limb proportions, the fundamental elastic properties of your connective tissue — these are structural. They set a range. Training moves you within the range, sometimes substantially. It does not relocate the range.

There is a case for finding this liberating rather than discouraging. The runner who spends five years trying to fix their form, chasing a stride they saw on video, is often trying to overcome a constraint that isn’t going anywhere — while neglecting the interventions that would have moved them meaningfully within the range they actually have.

Where this leaves the training week

If economy is the variable that separates runners with similar engines, and if it responds to volume, strength, plyometrics, and short fast running, then the implication for a training week is fairly plain — and fairly at odds with how most recreational runners train.

The economy work is the part that gets dropped. Strength training is what happens when there’s time. Strides are what you skip because the easy run is finished and you want to go home. Plyometrics belong, it is assumed, to sprinters.

Meanwhile the intervals — the sessions that hurt, the ones that feel like training — are pushing on a VO2 max that, for most experienced runners, is already close to its ceiling and moves very little.

There’s something almost perverse about it. The hardest work goes into the variable that has stopped responding, and the variable with room left is addressed with whatever attention survives the session.

The engine gets most of the effort. The cost of running it gets whatever’s left.