VO2 Max: Why Cardiorespiratory Fitness Is the Strongest Predictor of Longevity

Right, so. If you were only allowed to track one number about your body for the next decade, it probably shouldn’t be your weight, your cholesterol, or your step count. It should be your VO2 Max — the maximum amount of oxygen your body can actually use when you’re working as hard as you can.

It’s the fitness measure most tightly bound to how long you live. Which raises the obvious follow-up question, and the one almost nobody answers properly: is mine any good?

This post is the plain-English version — what VO2 Max is, what counts as a good score for someone your age and sex, why it predicts survival so well, and how to find out where you actually sit. The training plan is a separate post; I’ll point you at it at the end.

What VO2 Max actually is

VO2 Max measures the maximum volume of oxygen your body can use during intense exercise. It’s expressed in millilitres of oxygen per kilogram of body weight per minute (mL/kg/min).

It reflects the combined capacity of your:

• Heart to pump blood
• Lungs to oxygenate blood
• Blood vessels to deliver oxygen to muscles
• Muscles to extract and use oxygen

That’s the whole reason it works as a summary statistic. Most health numbers report on one system — a lipid panel tells you about your lipids, and that’s it. VO2 Max only goes up if the heart, lungs, vasculature and muscle are all doing their jobs, which makes it very hard to fake and very informative when it starts sliding.

What counts as a good VO2 Max for your age

A typical untrained 40-year-old male might have a VO2 Max around 35-40 mL/kg/min. An elite endurance athlete of the same age could be above 55-60. The gap represents a meaningful difference in cardiovascular health, metabolic function, and — as the research shows — life expectancy.

The raw number on its own is less useful than people think, though, because it’s heavily shaped by age and sex. This is why the published reference standards — the largest of them the FRIEND registry, which pooled US cardiopulmonary exercise tests and reported percentiles in ten-year age bands, separately for men and women (Kaminsky and colleagues, Mayo Clinic Proceedings, 2015) — rank people within their own band rather than against one universal threshold.

Two things follow from that, and between them they’re the reason “what’s a good VO2 max?” has no single answer.

Your band moves as you age. Reference values fall steadily across the age bands, so a number that puts a 30-year-old squarely in the middle of the pack puts a 60-year-old comfortably above it. In percentile terms, simply not declining is quietly an improvement.

Men’s and women’s bands are different. At the same age, women’s reference values sit below men’s — mostly haemoglobin mass, heart size and body composition, not effort. A 65-year-old woman at 32 mL/kg/min and a 30-year-old man at 50 can both be genuinely excellent for who they are. Comparing your number straight across to your partner’s is a category error, not a verdict.

So the honest question isn’t “is 38 good?” It’s “which percentile am I in, for my age and my sex?” Bit annoying if you wanted a single target to beat. But it’s the right way round, and it means the benchmark is always the version of you that didn’t train.

Why it predicts longevity

Part of the answer is the multi-system point above: the number can’t rise unless several organ systems are genuinely doing their jobs, which makes it very hard to fake and very informative when it starts sliding.

The rest is that the survival data agrees, consistently, across a lot of different populations — and it agrees without an obvious ceiling: in the largest single cohort, fitter people kept doing better right up to the top of the distribution. That evidence is observational, though, and that’s a real limitation rather than a footnote. It shows fitness and survival travelling together; it doesn’t show on its own that moving your own number buys you years. I took the landmark 2018 cohort apart properly — its design, what it actually measured, and the caveats the headlines skip — in the JAMA VO2 max study, dissected. If you want to know how much weight the evidence really bears, read that one.

Where the argument has landed in practice is the bit I find most telling: the American Heart Association’s 2016 scientific statement recommended clinicians assess cardiorespiratory fitness routinely and treat it as a clinical vital sign — sat alongside blood pressure and heart rate rather than below them. That’s an unusual thing to say about a fitness metric.

VO2 Max declines with age — but the rate is trainable

VO2 Max naturally declines by approximately 10% per decade after age 30. But this rate of decline is not fixed. Regular exercise, particularly high-intensity training, can slow the decline dramatically.

Studies of master athletes (competitive athletes in their 50s, 60s, and beyond) show VO2 Max values that would place them in elite categories for people decades younger. The body retains its capacity for cardiovascular adaptation well into old age.

This means that a 60-year-old who has trained consistently might have a VO2 Max comparable to an untrained 30-year-old. In biological age terms, their cardiovascular system is functioning decades younger than their chronological age.

For a practical way to translate this into one clear health number, read what biological age means in practice.

How to find out your number

A true VO2 Max is measured with a mask, on a treadmill or bike, in a graded test taken to exhaustion — that’s what the reference registries are built from, and it’s the only version that’s properly precise. Most people will never do one, which is fine.

Apple Watch estimates VO2 Max from outdoor walking and running workouts using heart rate data and movement patterns. It is not lab-accurate in absolute terms, but the estimates are consistent enough that the direction is trustworthy — and the direction is what you’re actually reading.

Sarvita pulls VO2 Max data from Apple Health and converts it to a VO2 Max Age using age-percentile reference tables, which is the percentile question above answered as one number instead of a table lookup. VO2 Max Age is one component of Sarvita’s overall biological age algorithm — alongside HRV Age and Body Composition Age — giving you a more complete picture than any single metric alone.

If you already track recovery with an Apple Watch app, it’s worth understanding how Sarvita compares to Athlytic: both read the same Apple Watch and HRV data, but Athlytic tells you how recovered you are today while Sarvita coaches your biological age over time.

Where to go if your number is low

The short version, because the long version belongs to another post: mostly easy aerobic volume, plus one genuinely hard session a week. The steepest part of the return curve is at the bottom, so going from unfit to moderately fit moves your percentile far more than going from good to elite ever will.

The long version, written out on a calendar with the heart rates filled in, is the 12-week VO2 max plan — three sessions a week, twelve weeks, one re-test at the end. For the reasoning behind the easy/hard split rather than the schedule, there’s the Zone 2 deep dive. And to see where cardio sits next to strength and stability, the four-pillar longevity training framework is the wider structure this fits into.

The practical takeaway

There is no single good VO2 Max. There’s a good VO2 Max for someone your age and your sex, and the only version of the question worth asking is which percentile you’re in — because that’s the form the reference tables come in, and it’s the form the survival data comes in too.

Two things worth holding onto. The number is unusually informative precisely because it’s hard to fake: it moves only when several systems are genuinely working, which is why the AHA was willing to call it a vital sign. And the steepest part of the curve is at the bottom, which is genuinely good news if you’re starting from the sofa rather than from “already quite fit and hoping to become elite”.

Find out where you sit first. The plan comes after.