VO2 Max, Lactate Threshold & Running Economy Explained

Among runners, it’s widely known that VO2 max, lactate threshold, and running economy are the three key factors that determine running performance.

But how many runners truly understand what these terms mean?

I’m a recreational runner who took up competitive training as an adult. I run around 500 km per month with a performance-focused mindset.

In this article, I’ll explain the three key determinants of running performance — VO2 max, lactate threshold, and running economy — in detail with clear diagrams.

Throughout this article, I’ll use VO2 max, LT, and RE as shorthand for maximal oxygen uptake, lactate threshold, and running economy, respectively.

The Three Factors That Determine Running Performance

The three key factors that determine running performance are VO2 max, LT, and RE. This framework was established in exercise physiology research — most notably Bassett & Howley (2000) ※1 — and is widely cited in endurance performance studies. The discussion here focuses primarily on full marathon performance.

One important nuance: LT is conceptually contained within VO2 max, and muscle fiber type affects both LT and RE — so these three factors are not entirely independent of one another.

The sections below explore VO2 max, lactate threshold, and running economy in detail.

VO2 Max: Your Body’s Aerobic Engine

VO2 max represents “how much oxygen your body can use per kilogram of body weight per minute.”

What Is VO2 Max?

Mitochondria produce energy (ATP) by combining oxygen with fuel substrates — carbohydrates, fat, protein, and lactate. The more oxygen your mitochondria can process, the more ATP they generate to power muscle contraction and drive running speed.

Bassett & Howley (2000) ※1 established that VO2 max and LT are independent determinants of running performance. Even at the same VO2 max, a higher LT — the exercise intensity at which lactate begins to accumulate — leads to better race performance.

While VO2 max and LT are related, it’s important to treat them as distinct concepts.

A high VO2 max does not necessarily mean you clear lactate quickly. It’s possible for an unusually high carbohydrate-based energy production capacity to elevate VO2 max without a corresponding improvement in lactate clearance rate.

It’s equally important to recognize that a high VO2 max does not directly translate to fast running speed.

No matter how high your VO2 max, if your running economy (RE) — the efficiency with which you convert energy into running speed — is low, your actual pace will be limited.

Think of it like a car engine that burns a lot of fuel but has poor fuel efficiency: plenty of power is generated, but you can’t sustain high speeds or maintain them for long.

How to Improve Your VO2 Max

For a detailed guide on training to improve your VO2 max, see the article below.

Lactate Threshold (LT): Your Endurance Ceiling

LT is determined by “how quickly you can process lactate” and “how well you can generate energy without producing lactate in the first place.”

What Is Lactate Threshold?

When carbohydrates exceed the mitochondria’s processing capacity, they are temporarily converted to lactate and released. That lactate has two main destinations. First, it can be taken up by cardiac muscle or slow-twitch muscle fibers and oxidized into ATP. Brooks (1986) ※2 showed that more than 75% of lactate produced during steady-state exercise is oxidized via this pathway.

The second destination is the bloodstream: lactate travels to the liver and is reconverted to glucose through gluconeogenesis.

A high LT means two things: ① you can clear lactate quickly, and ② you can generate energy while relying less on carbohydrates.

Point ② — generating energy while relying less on carbohydrates — means a greater proportion of your fuel comes from fat.

Fat oxidation and LT are often discussed as separate topics, but in reality, a high LT inherently includes a higher proportion of fat as an energy source.

How to Raise Your Lactate Threshold

For a detailed guide on training to raise your lactate threshold, see the article below.

Running Economy (RE): Efficiency of Energy Conversion

RE refers to “how efficiently you convert the energy you produce into running speed.”

What Is Running Economy?

The clearest illustration of RE is the difference between runners who excel at shorter distances and those who excel at longer distances.

Runners who tend to perform better at shorter distances often have a high VO2 max but lower RE. They’re good at generating large amounts of energy in a short time, but that energy isn’t converted efficiently — so performance drops over longer efforts.

Conversely, runners who tend to perform better at longer distances often have a lower VO2 max but higher RE. They don’t generate as much energy per minute, but they use it so efficiently that they can sustain performance over long distances.

How to Improve Your Running Economy

RE is shaped by two main factors: biomechanical factors and bioenergetic factors.

Both factors share a common thread: RE improves gradually over time. A review by Barnes & Kilding (2015) ※3 found that RE improves with cumulative training volume and running history — meaning consistent daily training is itself the primary driver of RE gains.

One reason experienced runners can still set personal records at relatively older ages is likely RE. Running economy tends to improve in proportion to accumulated training experience, and its importance increases as race distance grows longer.

This suggests that as the race distance increases, running economy plays an ever greater role — and that the returns on years of consistent training never fully disappear.

References

※1 Bassett DR Jr, Howley ET (2000) “Limiting factors for maximum oxygen uptake and determinants of endurance performance” Med Sci Sports Exerc

※2 Brooks GA (1986) “The lactate shuttle during exercise and recovery” Med Sci Sports Exerc

※3 Barnes KR, Kilding AE (2015) “Strategies to improve running economy” Sports Medicine