Your Garmin says your VO2max is 42. Your friend’s says 48. What does that mean? Less than you think.

VO2max — maximum oxygen consumption — is the maximum rate at which your body can take in, transport, and use oxygen during exercise. It’s measured in milliliters of oxygen per kilogram of body weight per minute (ml/kg/min). Higher numbers mean your aerobic engine has more capacity.

It is the most commonly cited fitness metric. It is also one of the most misunderstood.

What It Actually Measures

During maximal exercise, your body’s oxygen consumption follows a curve that eventually plateaus — you physically cannot use more oxygen even if the exercise intensity increases. That plateau is your VO2max.

In a lab, this is measured directly with a mask that analyzes the oxygen content of your exhaled air while you run on a treadmill at progressively harder intensities. The gold standard is precise, expensive, and something most recreational runners will never do.

Your watch estimates VO2max from pace and heart rate data using algorithms. These estimates are useful for tracking trends over time but can be off by 5-10% compared to lab measurements — and the accuracy varies significantly between devices and individual physiology.

What Determines It

Genetics. About 50% of your VO2max is determined by genetics.[1] This is the uncomfortable truth: some people have aerobic ceilings dramatically higher than others. Elite male distance runners typically have VO2max values of 70-85 ml/kg/min. The average untrained male is around 35-40. No amount of training will turn a genetic 45 into a genetic 80.

Training. The other 50% is trainable. Untrained individuals can typically improve VO2max by 15-25% through consistent endurance training. Already-trained runners see smaller improvements — 5-10% — because they’re closer to their genetic ceiling.

Age. VO2max declines approximately 1% per year after age 25-30. This is partly physiological aging and partly decreased training volume as life gets busier. The decline can be slowed (but not stopped) by maintaining consistent training.

Body composition. Because VO2max is expressed relative to body weight (ml/kg/min), losing weight increases your VO2max even without any cardiovascular improvement. This is math, not fitness.

Why It’s Overemphasized

Watch manufacturers love VO2max because it’s a single number that goes up when you train. It feels like a video game score. It provides the dopamine hit of measurable progress.

But here’s the problem: VO2max is the ceiling of your aerobic engine, not a predictor of how well you use that engine.

Two runners with identical VO2max values can run vastly different race times because of differences in:

  • Lactate threshold — what percentage of VO2max they can sustain
  • Running economy — how much oxygen they need at a given pace
  • Fatigue resistance — how well they maintain form and efficiency over distance
  • Mental toughness — their ability to sustain discomfort

A runner with a VO2max of 45 and excellent running economy will often beat a runner with a VO2max of 50 and poor economy at any distance beyond 800 meters.

What Pacewright Uses Instead

Pacewright doesn’t estimate VO2max from your watch data. Instead, it uses Jack Daniels’ VDOT system — which is derived from VO2max concepts but applied practically through race performance.[2]

VDOT takes your race result (time and distance) and calculates an equivalent fitness score. This score inherently includes all the factors that VO2max alone misses — your economy, your threshold, your fatigue resistance — because it’s based on what you actually did, not on an isolated physiological measurement.

Two runners with different VO2max values but identical 5K times will get the same VDOT score — because for the purpose of prescribing training, they’re equivalently fit.

Should You Care About Your VO2max?

As a trend: Yes. If your estimated VO2max is going up over months of training, you’re getting fitter. If it’s going down despite consistent training, something is off.

As an absolute number: Not much. Your VO2max relative to your genetic ceiling matters more than your VO2max relative to other people. A VO2max of 40 might represent 95% of one person’s potential and 65% of another’s.

As a training target: Not really. You don’t need to train specifically to raise your VO2max number. Train consistently, do your easy runs easy, do your hard runs hard, and your VO2max will improve as a byproduct of good training. Chasing the number on your watch leads to running easy days too fast (which improves the watch estimate without actually improving fitness).

As a race predictor: It’s a component, but an incomplete one. Your race performance is better predicted by your actual race times (via VDOT) than by a lab-measured or watch-estimated VO2max.