VO2 max: the fitness number that outpredicts smoking.

VO2 max is the maximum volume of oxygen your body can take in, transport and burn per minute during hard exercise — measured in millilitres of oxygen per kilogram of body weight per minute (mL/kg/min). It is a single number that summarises how well your lungs, heart, blood, blood vessels and muscle mitochondria work together. It is also, on the available evidence, the strongest measured predictor of all-cause mortality in adult medicine — stronger than smoking status, stronger than diabetes, stronger than established coronary artery disease. Almost no Australian has ever had it measured.

The key facts, up front

• Low fitness carried an adjusted hazard ratio of 5.04 for death versus elite fitness in a cohort of 122,007 adults — against 1.41 for smoking, 1.40 for diabetes and 1.29 for coronary artery disease.
• Every 1-MET improvement in fitness (roughly 3.5 mL/kg/min, or about 1 km/h faster running pace) was associated with 13% lower all-cause mortality and 15% lower cardiovascular event risk across 33 cohort studies.
• There was no upper limit of benefit. The fittest 2.3% of people had the lowest mortality of any group — no plateau, no U-shaped curve, no evidence of harm from very high fitness.
• The American Heart Association calls it a clinical vital sign and recommends that all adults have cardiorespiratory fitness measured or estimated annually.
• Only 22.4% of Australian adults aged 18–64 met the national physical activity guidelines in 2022, and 46.9% of employed adults described their working day as mostly sitting.

What the clinical evidence actually shows

Cardiorespiratory fitness has an unusually deep and consistent evidence base — which is why VO2 max sits alongside the blood markers in The HodieLabs Evidence-Based Clinical Library rather than being treated as a sports-performance curiosity.

• Cleveland Clinic cohort (Mandsager et al. JAMA Network Open 2018): 122,007 consecutive adults referred for treadmill testing, followed over 1.1 million person-years. Risk-adjusted all-cause mortality fell in a dose-dependent way with every increment of fitness. Elite performers (fitness two standard deviations above the age- and sex-matched mean) had an 80% lower adjusted mortality risk than the least fit — and elite still beat merely high fitness (adjusted HR 0.77). The authors found no ceiling to the benefit.
• Kodama meta-analysis (JAMA 2009): 33 cohort studies, 102,980 participants for the mortality analysis. Each 1-MET higher maximal aerobic capacity was associated with a relative risk of 0.87 for all-cause mortality and 0.85 for coronary/cardiovascular events. Adults below 7.9 METs had substantially higher event rates than those above it.
• American Heart Association scientific statement (Ross, Blair, Arena et al. Circulation 2016): the formal synthesis, concluding that cardiorespiratory fitness is as powerful a predictor of cardiovascular and mortality risk as hypertension, smoking, obesity, dyslipidaemia and type 2 diabetes — and that adding it to standard risk models meaningfully improves risk classification. Hence the recommendation to treat fitness as a vital sign.
• Aerobics Center Longitudinal Study (Blair et al. JAMA 1989 and 1995): the foundational work. The 1989 paper established the fitness–mortality gradient in healthy men and women; the 1995 follow-up of 9,777 men found that those who moved from unfit to fit between two examinations had a 44% lower age-adjusted all-cause mortality risk, and 52% lower cardiovascular mortality, than men who stayed unfit.

Where the evidence is weaker — and why that matters

An honest reading has to include the caveats, because the caveats change how the number should be used.

Almost all of this is observational. Fitness is not randomly assigned. People with high VO2 max tend to be leaner, less inflamed, better slept and free of the occult illness that quietly suppresses exercise capacity years before diagnosis. Reverse causation — sickness lowering fitness rather than low fitness causing sickness — is a genuine and largely unfixable problem in this literature. The Cleveland Clinic authors say so explicitly.

The "unfit to fit" finding has been directly challenged. Williams (Medicine & Science in Sports & Exercise, 2003) simulated the Aerobics Center design and showed that measurement error alone — people being reclassified between visits simply because treadmill performance varies — could reproduce much of the apparent mortality benefit of "improving" fitness. Regression to the mean is a real competitor explanation for part of that 44%.

The best randomised test was null on its primary outcome. The Generation 100 trial (Stensvold et al. BMJ 2020) randomised 1,567 Norwegians aged 70–77 to five years of supervised high-intensity interval training, moderate continuous training, or standard national guideline advice. All-cause mortality did not differ significantly between the combined exercise groups and the control group. Two caveats cut the other way: the control group was itself unusually active, and the whole trial population outlived the Norwegian norm for their age band, which is precisely what you would expect if activity helps and the "control" was not really inactive.

The defensible position is therefore: VO2 max is an exceptionally strong prognostic marker, the intervention that raises it is safe and beneficial across dozens of other outcomes, and the direct randomised mortality evidence is thinner than the headlines suggest. That is still an easy case for measuring it.

How HodieLabs reads your VO2 max

Every marker in the HodieLabs Evidence-Based Clinical Library is interpreted against published clinical authority standards and age- and sex-matched norms — never a single arbitrary "optimal" cut-off. For VO2 max:

• Below 30 mL/kg/min — low fitness in an adult of any age. This is the band where the mortality signal in the cohort data is strongest, and it is treated as an actionable finding even when every blood marker is normal.
• Below roughly 38 mL/kg/min (men) or 32 mL/kg/min (women) between ages 35 and 50 — below age-expected. Midlife fitness is strongly predictive of outcomes two to three decades later, and this is the decade in which the number responds best to training.
• Trend over time is the primary signal. VO2 max declines with age in everyone. A flat or rising line across serial testing is a better result than any one-off percentile.

Critically, VO2 max is read alongside the bloods, not instead of them. A high VO2 max with elevated hs-CRP means inflammation that fitness is not masking. A low VO2 max with a normal HbA1c and a clean lipid panel is the classic hidden risk: perfect-looking bloods, deconditioned cardiovascular system. A rising TG:HDL ratio alongside falling fitness points at insulin resistance well before glucose moves. And a VO2 max that will not improve despite consistent training frequently traces back to oxygen delivery — low haemoglobin or depleted iron stores — rather than to lack of effort.

What actually raises VO2 max

The training evidence is more robust than the mortality evidence, because it is largely randomised.

• A base of low-intensity aerobic volume. Zone 2 work — a conversational pace you could hold for an hour — three to four times a week for 30 to 45 minutes builds the mitochondrial and capillary density that raises your ceiling. This is the unglamorous majority of the work.
• One to two high-intensity sessions per week. Intensity is what moves the peak. In Wisløff et al. (Circulation 2007), 12 weeks of aerobic interval training at 95% of peak heart rate raised VO2 peak by 46% in post-infarction heart failure patients, versus 14% for moderate continuous training at 70% — alongside reverse left-ventricular remodelling and a 40% fall in pro-BNP. Healthy, already-active people should expect far smaller percentage gains; the deconditioned have the most to gain.
• Consistency measured in months, not weeks. Eight to twelve weeks is the realistic window for a measurable change, and detraining reverses it faster than training built it.
• The Australian guideline floor is a floor, not a target. 150–300 minutes of moderate or 75–150 minutes of vigorous activity per week, plus two strength sessions, is the national minimum for adults 18–64. The cohort data show benefit continuing well beyond it.

The Australian gap

In the 2022 National Health Survey, only 22.4% of Australian adults aged 18–64 met the physical activity guidelines, and nearly half of employed adults (46.9%) described a typical workday as mostly sitting. Compliance falls with age exactly as cardiovascular risk rises: 31.3% of 18–24 year olds met the guidelines, against 16.1% of 55–64 year olds. Meanwhile VO2 max is essentially absent from routine Australian primary care — a standard health check measures blood pressure, cholesterol and glucose, and never touches the variable with the largest hazard ratio in the room. Consumer wearables from Garmin, Apple, WHOOP and Oura have quietly put an estimate in millions of Australian pockets, but almost nobody has had that estimate interpreted by a clinician or validated against a proper test.

How measurement works at HodieLabs

VO2 max is part of the fitness assessment in every Health Blueprint at our Melbourne Preventative Health & Longevity Clinic, read against age- and sex-matched norms and integrated with your blood panel, body composition and wearable data rather than in isolation. Because it is one of the few longevity markers that responds strongly and quickly to a specific intervention, it also anchors the training prescription — and it feeds the biological age calculation, where a low VO2 max is one of the heaviest single penalties applied.

The bottom line

VO2 max is the rare marker that is simultaneously the strongest predictor of dying, one of the most modifiable things about you, and almost never measured. The randomised mortality evidence is genuinely incomplete, and anyone telling you that raising your VO2 max is proven to extend your life is overstating the data. But between a hazard ratio that dwarfs every traditional risk factor, an intervention with a better safety profile than any drug, and an evidence base for training that is unambiguous — the case for knowing your number, and knowing which way it is trending, is about as strong as preventative medicine gets. For more on why this distinction matters, see our piece on healthspan versus lifespan.

References

1. Mandsager K, Harb S, Cremer P, Phelan D, Nissen SE, Jaber W. Association of cardiorespiratory fitness with long-term mortality among adults undergoing exercise treadmill testing. JAMA Netw Open. 2018;1(6):e183605.
2. Kodama S, Saito K, Tanaka S, et al. Cardiorespiratory fitness as a quantitative predictor of all-cause mortality and cardiovascular events in healthy men and women: a meta-analysis. JAMA. 2009;301(19):2024–2035.
3. Ross R, Blair SN, Arena R, et al. Importance of assessing cardiorespiratory fitness in clinical practice: a case for fitness as a clinical vital sign. A scientific statement from the American Heart Association. Circulation. 2016;134(24):e653–e699.
4. Blair SN, Kohl HW 3rd, Paffenbarger RS Jr, Clark DG, Cooper KH, Gibbons LW. Physical fitness and all-cause mortality: a prospective study of healthy men and women. JAMA. 1989;262(17):2395–2401.
5. Blair SN, Kohl HW 3rd, Barlow CE, Paffenbarger RS Jr, Gibbons LW, Macera CA. Changes in physical fitness and all-cause mortality: a prospective study of healthy and unhealthy men. JAMA. 1995;273(14):1093–1098.
6. Williams PT. The illusion of improved physical fitness and reduced mortality. Med Sci Sports Exerc. 2003;35(5):736–740.
7. Stensvold D, Viken H, Steinshamn SL, et al. Effect of exercise training for five years on all cause mortality in older adults (the Generation 100 study): randomised controlled trial. BMJ. 2020;371:m3485.
8. Wisløff U, Støylen A, Loennechen JP, et al. Superior cardiovascular effect of aerobic interval training versus moderate continuous training in heart failure patients: a randomized study. Circulation. 2007;115(24):3086–3094.
9. Australian Bureau of Statistics. Physical activity, 2022. National Health Survey. Released 15 December 2023.
10. Australian Government Department of Health and Aged Care. Physical activity and exercise guidelines for all Australians — for adults (18 to 64 years).

This article is general information, not medical advice. Speak with your GP about what testing and care is appropriate for you.