Peter Attia calls it the single most powerful marker of how long you’ll live. Longevity clinics charge thousands of dollars to measure it as part of a “performance health assessment.” And if you own an Apple Watch, Garmin, or WHOOP, a number claiming to be it is quietly sitting in your fitness app right now, updating itself while you sleep.
VO2 max — your body’s maximum capacity to take in and use oxygen during hard exercise — has become the wellness world’s favorite biomarker almost overnight. Search interest has climbed for years, driven by Outlive, the “Zone 2 training” boom, and a wearable industry that turned a once-obscure exercise-physiology metric into a number people obsess over the way they used to obsess over step counts. And yet, look for a rigorous, independent answer to the two questions that actually matter — how accurate is the number your device is showing you, and does raising it actually make you live longer — and you’ll mostly find marketing copy from wearable brands, SEO content from supplement companies, and dense exercise-science papers that assume a kinesiology degree.
That gap is what this article is for. The short version: the population-level evidence linking fitness to survival is some of the strongest in all of preventive medicine. The wearable number in your pocket is a rough guess with a real error margin most people never see. And a genuinely important 2025 study, largely absent from consumer coverage, complicates the simple story that a higher number causes a longer life.
Key takeaways
- Cardiorespiratory fitness is one of the most consistently validated predictors of all-cause mortality in medicine — a 2018 study of 122,007 people found no upper limit to the survival benefit of higher fitness, and the American Heart Association has called for it to be treated as a clinical vital sign.
- A 2025 Mendelian randomization study — a genetic method built to test causation, not just correlation — found VO2 max was not independently causal for longevity once body composition and physical activity were accounted for. Fitness may be more of a marker of good health than an independent cause of a longer life.
- Wearable VO2 max estimates carry real, documented error: a 2025 validation study found Apple Watch underestimates lab-measured VO2 max with a 13.31% average error; Garmin performs better with a chest strap than wrist-only sensing; WHOOP’s estimate leans heavily on resting data rather than a maximal effort.
- A genuine lab-measured VO2 max requires a cardiopulmonary exercise test (CPET) with direct gas analysis — the only true gold standard — and typically costs $150 to $400 at a fitness lab, or $300-$600+ clinically.
- “Good” VO2 max values differ enormously by age and sex; comparing your number to a generic online benchmark, rather than an age- and sex-matched one, is one of the most common ways people misjudge their own fitness.
- VO2 max is genuinely trainable — structured aerobic and interval training has been shown to raise it by roughly 15-20% within 8-12 weeks — which matters more practically than chasing precision in the number itself.
Quick Answer: Do You Actually Need a Lab VO2 Max Test?
| Your situation | What the evidence suggests |
|---|---|
| Generally healthy, exercising casually, just curious | A wearable estimate (understood with its error margin) or a submaximal field test is enough — a $300+ lab test adds little practical value |
| Training seriously for endurance performance (running, cycling, triathlon) | A lab CPET is genuinely useful — it gives training zones based on your actual physiology, not an estimate |
| Considering it as a “longevity” data point at a concierge or performance clinic | Reasonable as one data point among many, but treat the single number cautiously — see the causation section below before assuming a higher score itself extends your life |
| Unexplained shortness of breath, chest symptoms, or a cardiology referral | A clinical CPET is a real diagnostic tool here, typically ordered and often covered by insurance — this is a different use case from wellness testing |
| Relying entirely on a smartwatch number to judge your health | Treat it as a rough trend indicator only — published error rates of 5-13%+ mean a single reading isn’t precise enough to anchor decisions on |
Not sure whether VO2 max testing — or any other preventive test — actually fits your goals? Answer a few quick, non-identifying questions and get personalized eligibility guidance across all 6 categories ScanGlean covers. Take the Fit Check →
What Is VO2 Max, Exactly?
VO2 max (maximal oxygen uptake) is the highest rate at which your body can absorb, transport, and use oxygen during progressively harder exercise, expressed as milliliters of oxygen consumed per kilogram of body weight per minute (mL/kg/min). It’s a measure of the entire chain that gets oxygen from the air into your working muscles: how well your lungs extract it, how much your heart can pump, how much oxygen your blood can carry, and how efficiently your muscle cells can use it once it arrives.
Because it depends on so many systems working together, VO2 max functions as a genuine whole-body integration score — which is a large part of why it correlates with so many different health outcomes, not just athletic performance.
Why It Suddenly Became the Longevity World’s Favorite Number
The scientific case for taking cardiorespiratory fitness seriously isn’t new. In 2016, the American Heart Association published a scientific statement — led by researcher Robert Ross and colleagues, in Circulation — arguing that fitness should be measured or estimated in every adult, “at a minimum… each year,” and treated as a clinical vital sign on par with blood pressure, similar to how it’s long been treated in exercise-science research. That statement was formally updated in 2024 with additional supporting evidence.
What changed is the audience. Outlive, physician Peter Attia’s 2023 bestseller, popularized VO2 max as a centerpiece of his “Centenarian Decathlon” framework, explicitly framing high aerobic capacity as one of the most trainable, most consequential levers for extending both lifespan and healthspan. At roughly the same time, consumer wearables — Garmin first, then Apple Watch, then WHOOP and Oura — began displaying an estimated VO2 max number to ordinary users with zero exercise-physiology background, no context about margin of error, and often a colored “fitness age” attached to it. A metric that used to live exclusively in university exercise-physiology labs and elite sports programs is now a badge people screenshot and compare.
The Evidence That Built VO2 Max’s Reputation
Strip away the hype, and the underlying research is genuinely some of the most robust in preventive medicine.
The foundational meta-analysis. In 2009, researcher Satoru Kodama and colleagues published a meta-analysis in JAMA pooling 33 studies covering nearly 103,000 people. It found that each 1-MET increase in cardiorespiratory fitness (roughly the metabolic cost of walking briskly) was associated with a 13% reduction in all-cause mortality and a 15% reduction in cardiovascular events. People with low fitness had 70% higher all-cause mortality than people with high fitness.
The “no ceiling” study. The most cited recent evidence comes from a 2018 study in JAMA Network Open, led by researcher Kyle Mandsager and colleagues at Cleveland Clinic, following 122,007 patients who underwent treadmill stress testing between 1991 and 2014. Compared with the least-fit group, people classified as “elite” (roughly two standard deviations above their age-matched average) had about an 80% lower risk of death — and critically, the survival benefit kept increasing all the way to the top of the fitness distribution, with no observed plateau. As senior investigator Wael Jaber put it, “there was no ceiling for benefit.” That’s an unusual finding in medicine, where most risk factors show diminishing returns at the extremes.
The long-view evidence. A 2018 study in the Journal of the American College of Cardiology, led by researcher Johan Clausen using the Copenhagen Male Study — one of the longest-running cohorts with objectively measured fitness — followed middle-aged men for 46 years and found that higher midlife cardiorespiratory fitness was associated with lower mortality risk that persisted for decades afterward, making it one of the longest human follow-up studies linking a single fitness measurement to lifelong outcomes.
Taken together, these are not small or shaky findings. They’re large, well-replicated, and consistent across different countries, decades, and study designs — which is exactly why VO2 max earned its reputation as one of medicine’s most powerful single predictors of survival.
The Twist Almost No One Reports: Is It Actually Causal?
Here’s where the popular narrative gets ahead of the science, and where this article differs from almost everything else you’ll find on this topic.
All of the studies above are observational: they measure people’s fitness once (or a few times) and track what happens to them afterward. Observational studies are excellent at showing that two things move together; they’re structurally unable to prove that one causes the other. Fitter people also tend to have less visceral fat, exercise more consistently, smoke less, and have fewer chronic conditions to begin with — any of which could be doing the real work, with VO2 max simply riding along as a marker.
In 2025, researchers Alisa Kjaergaard, Christina Ellervik, and colleagues published a study in the Journal of Clinical Endocrinology & Metabolism that directly tested this question using Mendelian randomization — a method that uses naturally occurring genetic variation as a kind of randomized experiment, since the genetic variants that influence a trait like fitness are assigned essentially at random at conception, sidestepping many of the confounding factors that plague standard observational research. Using genome-wide data, the researchers examined whether genetically predicted VO2 max had an independent causal effect on longevity, after separately accounting for body composition and physical activity.
Their finding: VO2 max was not causally associated with longevity once these other factors were accounted for. In other words, the genetic version of the experiment suggests that fitness itself may be more of a downstream marker of good metabolic health, favorable body composition, and consistent activity — rather than an independent lever that, on its own, extends life.
This doesn’t overturn everything above. It’s worth being precise about what it does and doesn’t mean:
- It doesn’t mean exercise is worthless — physical activity itself remained relevant in the same analysis, and there’s a large, separate body of randomized-trial evidence that exercise improves cardiovascular risk factors, cognitive function, and quality of life regardless of how it moves a VO2 max number.
- It doesn’t mean the observational mortality data is wrong — a 122,007-person study with an 80% mortality difference between top and bottom groups is a real, measured pattern, not a statistical artifact.
- It does mean that treating “raise my VO2 max number” as the causal goal — as opposed to a signal that reflects genuinely healthy behaviors and body composition — may be aiming at the wrong target. The number appears to be a very good report card, not necessarily the thing doing the work.
This is exactly the kind of nuance that gets lost between “landmark 122,000-person study” and a wearable notification telling you your fitness age just improved by two years.
How Is VO2 Max Actually Measured?
The gold standard: cardiopulmonary exercise testing (CPET). In a lab or clinical setting, you exercise on a treadmill or stationary bike at progressively increasing intensity while breathing through a mask connected to a metabolic cart that directly measures the oxygen you inhale and the carbon dioxide you exhale. The test continues until you reach true volitional exhaustion, at which point your oxygen consumption plateaus despite increasing effort — that plateau is your actual, directly measured VO2 max. This is the only method that measures the thing itself, rather than estimating it.
Submaximal field tests. For people who can’t or don’t want to reach true exhaustion, several validated field tests estimate VO2 max from a lower-intensity effort: the Rockport 1-mile walk test, the Cooper 12-minute run test, and various step-test and cycle-ergometer protocols. These trade some accuracy for accessibility and safety, and are commonly used in research and general fitness settings rather than elite sport or clinical diagnosis.
Non-exercise prediction equations. Perhaps the least well-known option: researchers have developed equations that estimate VO2 max using no exercise at all — just age, sex, BMI, resting heart rate, and a self-reported physical activity questionnaire. The best-known version, developed by researcher Radim Jurca and colleagues and published in the American Journal of Preventive Medicine using data from nearly 50,000 people across three cohorts, achieves a standard error of estimate in the range of roughly 8-15%. That’s a genuinely useful tool for large research studies, and a reasonable ballpark for personal curiosity — but not a substitute for direct measurement when precision actually matters.
Wearable Estimates vs. Lab Tests: How Big Is the Gap?
This is the part most people never see, because the number on your wrist arrives with total confidence and zero error bars.
| Device / Method | How it estimates VO2 max | Documented accuracy vs. lab CPET |
|---|---|---|
| Cardiopulmonary exercise test (CPET) | Direct gas exchange analysis during a maximal effort | Gold standard — this is the reference measurement everything else is compared against |
| Garmin (Firstbeat algorithm) with chest strap | Heart rate response during outdoor runs, combined with pace and personal data | Roughly 5-7% mean error in independent validation |
| Garmin, wrist-only optical heart rate | Same algorithm, less reliable heart rate input | Roughly 5-8 mL/kg/min error — noticeably worse than with a chest strap |
| Apple Watch | Heart rate and speed data collected passively over several outdoor walks/runs (no dedicated maximal test) | 13.31% mean absolute error and a 6.07 mL/kg/min average underestimation in a 2025 peer-reviewed validation study |
| WHOOP | Modeled primarily from resting physiological data, activity history, and demographics rather than a maximal-effort test | No dedicated maximal effort measurement; independent reviewers describe wider uncertainty than exercise-based wearable estimates |
| Non-exercise prediction equation | Age, sex, BMI, resting heart rate, activity questionnaire | ~8-15% standard error of estimate in validation research |
A few things worth understanding about why this gap exists: none of these consumer devices measure oxygen consumption directly — they infer it from proxies like heart rate and pace, run through a proprietary algorithm the company doesn’t fully disclose. That’s not necessarily dishonest, but it does mean the “VO2 max” number on your wrist is a modeled estimate wearing the same label as a clinically measured value, which invites people to treat it with far more precision than it has earned.
It’s also worth noting the direction of the error matters. Apple Watch’s roughly 13% underestimation, for example, means someone genuinely in the “excellent” fitness category by lab standards might see a wearable number that reads as merely “good” — a real source of unwarranted concern, or unwarranted motivation to chase a number that was never accurate in the first place.
What Counts as a “Good” VO2 Max?
This is where a lot of the internet’s VO2 max content quietly misleads people: benchmark numbers thrown around casually (like “40 is good” or “50 is elite”) almost never specify age or sex, even though both change the answer dramatically.
Using normative data from the Cooper Institute’s Aerobics Center Longitudinal Study — a cohort of more than 80,000 adults who completed maximal treadmill tests with direct gas analysis, published in the American College of Sports Medicine’s Guidelines for Exercise Testing and Prescription (11th edition) — fitness is categorized by age- and sex-specific percentiles: below the 20th percentile is “Poor,” 20th-39th “Fair,” 40th-59th “Average,” 60th-79th “Good,” 80th-94th “Excellent,” and 95th and above “Superior.”
| Age | Men — 50th percentile (Average) | Men — Excellent threshold | Women — 50th percentile (Average) | Women — Excellent threshold |
|---|---|---|---|---|
| 25 | ~44 mL/kg/min | ~54 mL/kg/min | ~35 mL/kg/min | ~41 mL/kg/min |
| 35 | ~42 mL/kg/min | ~49 mL/kg/min | ~30 mL/kg/min | ~36 mL/kg/min |
| 45 | ~38 mL/kg/min | ~45 mL/kg/min | ~28 mL/kg/min | ~33 mL/kg/min |
| 55 | ~34 mL/kg/min | ~41 mL/kg/min | ~24 mL/kg/min | ~29 mL/kg/min |
(Figures are approximate midpoints drawn from published ACSM/Cooper Institute normative tables and will vary somewhat by source and test protocol; treat them as a general reference, not a precise personal benchmark.)
Across every age bracket, men score roughly 15-20% higher than women on average — a gap driven by real physiological differences (higher hemoglobin concentration and oxygen-carrying capacity, larger heart size relative to body weight, and higher lean muscle mass), not a difference in effort or training. Comparing a woman’s VO2 max directly against a man’s, without adjusting for this, is one of the more common ways people misjudge where they actually stand.
The Psychology of Chasing a Number
This is where fitness tracking runs into the same psychological trap that ScanGlean has flagged in other corners of preventive health, from continuous glucose monitors to biological age clocks: a device hands you a precise-looking number, and precision gets mistaken for accuracy.
The “fitness age” framing effect. Several apps and wearables now convert your VO2 max estimate into a “fitness age” — telling you, for instance, that despite being 42, your body tests as 34. This is the same underlying data, reframed to trigger a stronger emotional response, and it works: an age number feels personal and identity-relevant in a way a raw mL/kg/min figure doesn’t. It also means the same 13% wearable error margin gets inherited by a number people take even more personally than the original metric.
Comparison without context. Fitness apps and social platforms make it trivially easy to compare your number to a friend’s, a stranger’s, or an “elite athlete” benchmark — almost always without controlling for age or sex, the two variables shown above to change the expected number by 15-20% or more. A 45-year-old woman comparing her VO2 max to a 25-year-old man’s isn’t measuring the same thing the numbers imply she’s measuring.
Treating a wearable trend as a diagnosis. A single VO2 max reading that dips after a bad night’s sleep, an illness, or a stressful week can read as alarming on an app dashboard, when the underlying error margin (5-13%+ depending on device) means day-to-day noise is often larger than any real physiological change. The appropriate use of a wearable estimate is as a rough, long-run trend line — not a number to react to daily.
The causal-goal trap. As covered above, the 2025 Mendelian randomization findings suggest the healthiest mental model isn’t “I need to raise this specific number because the number itself extends my life” — it’s “this number tends to reflect genuinely healthy behaviors, so building those behaviors is the actual goal, and the number is feedback, not the target.” That’s a subtle but meaningful reframe, and it’s one almost no wearable marketing copy makes room for.
So, Should You Get a Real Lab Test?
For most healthy adults who are simply curious, the honest answer is: probably not necessary. A well-calibrated wearable estimate — understood with its real error margin — or a submaximal field test gives a reasonable trend signal for a fraction of the cost, and the research above suggests the specific number matters less than the underlying behaviors it reflects.
A lab-measured CPET earns its cost in a narrower set of situations:
- You’re training seriously for endurance performance (marathon, triathlon, competitive cycling) and want scientifically accurate training zones based on your actual physiology rather than an estimated one.
- You want a genuinely precise baseline before starting a structured fitness program, to measure real improvement rather than device-to-device noise.
- A physician has ordered one for a medical reason — unexplained shortness of breath, pre-surgical risk assessment, or evaluating exercise capacity in the context of a diagnosed condition. This is a different context from wellness curiosity, and it’s the version most likely to be covered by insurance.
- You’re at a longevity or performance clinic that includes it as one input among many (alongside DEXA body composition, bloodwork, and a physician review) rather than presenting the number itself as the product.
Typical costs in the U.S. as of 2026: a fitness-focused test at a university exercise lab or performance studio generally runs $99 to $250; boutique performance labs and some big-city facilities charge $175 to $400, particularly when bundled with a detailed physiological report and coaching consultation; a clinical CPET ordered for a medical reason typically costs $300 to $600 or more but is frequently covered by insurance, unlike the wellness version, which almost never is.
Can You Actually Improve Your VO2 Max — and Is That the Right Goal?
Whatever your view on the causation question above, VO2 max is genuinely one of the more trainable fitness metrics available, and improving it comes bundled with benefits that don’t depend on resolving the causality debate.
Sustained moderate-intensity (“zone 2”) training — long, steady efforts at an intensity where you can still hold a conversation — builds the aerobic base and mitochondrial capacity that underlies fitness improvements over months of consistent practice.
High-intensity interval training has repeatedly shown some of the fastest gains in controlled research. The Norwegian 4x4 protocol (four 4-minute intervals at roughly 85-95% of maximum heart rate, separated by active recovery), studied extensively by exercise physiologist Jan Helgerud and colleagues, has been shown to meaningfully raise VO2 max in both healthy adults and clinical populations, often faster than continuous moderate exercise alone.
Across various controlled training studies, previously untrained or moderately trained adults commonly see VO2 max improvements in the range of 15-20% over 8-12 weeks of consistent structured training, with smaller incremental gains continuing over subsequent months. Genetics play a real role too — twin and family studies have found substantial individual variation in “trainability,” meaning two people doing an identical program can see meaningfully different results.
The practical takeaway, consistent with the causal-goal reframe above: training for a higher VO2 max and training for genuinely better cardiovascular health point you toward the same behaviors — consistent aerobic exercise, a mix of intensities, and enough volume over time. Chasing the training is likely to serve you better than chasing the number.
Where VO2 Max Fits in the Longevity Clinic Landscape
VO2 max testing has become a standard inclusion at many concierge longevity and performance clinics, typically bundled alongside DEXA body composition scans, comprehensive bloodwork, and a physician consultation rather than sold as a standalone product. We cover specific providers and pricing — including how VO2 max testing factors into programs at Biograph, Fountain Life, and other leading U.S. longevity clinics — in our full clinic-by-clinic comparison.
As a standalone diagnostic component, VO2 max testing (done properly, in a lab, with direct gas analysis) is one of the more genuinely evidence-backed tools these clinics offer — considerably more validated than some of the newer, less-established tests bundled into the same packages. The caution isn’t about the test’s validity; it’s about making sure the number gets interpreted with the nuance this article has laid out, rather than as a simple “higher score, longer life” scoreboard.
The Bottom Line
The evidence connecting cardiorespiratory fitness to survival is genuinely some of the strongest in preventive medicine — large, repeated, and remarkably consistent across decades of research. That part of the VO2 max story deserves the attention it’s gotten.
What deserves more attention than it currently receives: the number on your wearable carries a real, published error margin that most marketing never mentions; “good” and “excellent” mean very different things depending on your age and sex; and a rigorous 2025 genetic study found the relationship between VO2 max and longevity may not be causal once body composition and activity are accounted for — suggesting the number is likely more of a report card for healthy behavior than a lever you pull directly.
None of that makes fitness testing worthless. It means the most useful way to relate to your VO2 max — wearable-estimated or lab-measured — is as a rough, honest trend indicator of the training you’re actually doing, not a precise score to optimize for its own sake.
Curious which preventive tests are actually worth your time and money? Answer a few quick, non-identifying questions and get personalized eligibility guidance across all 6 categories ScanGlean covers. Take the Fit Check →
Frequently Asked Questions
What is VO2 max and why do longevity clinics test it?
VO2 max is the maximum rate at which your body can take in, transport, and use oxygen during intense exercise, measured in milliliters of oxygen per kilogram of body weight per minute (mL/kg/min). Longevity clinics test it because cardiorespiratory fitness is one of the most consistently validated predictors of all-cause mortality in the medical literature — a 2016 American Heart Association scientific statement recommended it be treated as a clinical vital sign alongside blood pressure and cholesterol.
Is VO2 max really the best predictor of how long you’ll live?
Among measurable health markers, it’s one of the strongest. A landmark 2018 JAMA Network Open study of 122,007 patients undergoing treadmill testing found cardiorespiratory fitness had a stronger, more linear relationship with survival than smoking, diabetes, or hypertension, with no observed ceiling — the fittest group had roughly 80% lower mortality than the least fit. A 2009 JAMA meta-analysis of 33 studies found each 1-MET increase in fitness cut all-cause mortality risk by about 13%. That said, a 2025 Mendelian randomization study raised real questions about whether the relationship is causal — see below.
How accurate are wearable VO2 max estimates from Apple Watch, Garmin, or WHOOP?
Less accurate than most people assume, and the gap varies significantly by brand and hardware. A 2025 PLOS ONE validation study found Apple Watch underestimated lab-measured VO2 max by an average of 6.07 mL/kg/min, with a mean absolute percentage error of 13.31%. Garmin’s Firstbeat algorithm performs better with a chest strap (roughly 5-7% error) than with wrist-only optical heart rate sensing (5-8 mL/kg/min error). WHOOP estimates VO2 max primarily from resting physiological data and demographics rather than a maximal effort test, which independent reviewers say produces wider uncertainty than exercise-based estimates.
Does raising your VO2 max actually make you live longer?
This is genuinely unsettled, and it’s the part most consumer content skips entirely. Large observational studies consistently link higher fitness to lower mortality. But a 2025 Journal of Clinical Endocrinology & Metabolism study using Mendelian randomization — a genetic method designed to test causation rather than mere association — found VO2 max was not causally linked to longevity once body composition and physical activity were accounted for, suggesting fitness may be more of a marker of good health than an independent cause of it. That doesn’t mean exercise is pointless; it means the specific number on your wearable may matter less than the behaviors that produce it.
What is considered a “good” VO2 max for my age?
It depends heavily on age and sex, which is why single benchmark numbers you see online are often misleading. Using ACSM/Cooper Institute normative data, a 35-year-old man’s 50th percentile is roughly 42 mL/kg/min, with “excellent” starting around 49; a 35-year-old woman’s 50th percentile is roughly 30 mL/kg/min, with “excellent” starting around 36. Men typically score 15-20% higher than women at every age due to differences in hemoglobin, heart size, and lean mass — a difference that reflects physiology, not fitness level.
How much does a real VO2 max test cost, and do I need a lab test?
A fitness-focused lab test at a university exercise lab or performance studio typically runs $99 to $250; add-on packages at longevity clinics or specialty gyms can run $175 to $400. A clinical cardiopulmonary exercise test (CPET), ordered for a medical reason like unexplained shortness of breath, typically costs $300 to $600+ but is often covered by insurance when medically indicated, unlike the wellness version. Most healthy adults curious about their fitness don’t need a lab test — a well-run submaximal field test or an honest read of a wearable estimate’s error margin is enough for general purposes.
What’s the difference between a lab VO2 max test and a wearable estimate?
A lab test (cardiopulmonary exercise test) measures oxygen consumption directly, using a mask connected to a gas analyzer while you exercise to true exhaustion on a treadmill or bike — this is the scientific gold standard. A wearable estimate uses an algorithm that infers VO2 max from heart rate, pace, and personal data during submaximal effort, without ever measuring actual gas exchange. Non-exercise prediction equations, used in some large research studies, estimate it from age, resting heart rate, BMI, and activity questionnaires alone, with a standard error of roughly 8-15%.
Can you actually improve your VO2 max, and how long does it take?
Yes — it’s one of the more trainable fitness metrics. Structured aerobic training, including sustained moderate-intensity (“zone 2”) work and high-intensity interval protocols like the Norwegian 4x4 method, has been shown in controlled studies to raise VO2 max by roughly 15-20% over 8-12 weeks in previously untrained or moderately trained adults, with continued smaller gains over months of consistent training. Genetics also set a meaningful ceiling — trainability itself varies substantially between individuals.
This article is for general educational and informational purposes only. It is not medical advice, and it is not a substitute for diagnosis, treatment, or guidance from a licensed physician or other qualified healthcare provider. Anyone with cardiovascular symptoms, a heart condition, or other significant health concerns should consult a physician before undertaking maximal exercise testing or a new high-intensity training program.
Sources
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- 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.
- Mandsager K, Harb S, Cremer P, et al. Association of Cardiorespiratory Fitness With Long-Term Mortality Among Adults Undergoing Exercise Treadmill Testing. JAMA Network Open, 2018;1(6):e183605.
- Clausen JSR, Marott JL, Holtermann A, et al. Midlife Cardiorespiratory Fitness and the Long-Term Risk of Mortality: 46 Years of Follow-Up. Journal of the American College of Cardiology, 2018;72(9):987-995.
- Kjaergaard AD, Ellervik C, Jessen N, Lessard SJ. Cardiorespiratory Fitness, Body Composition, Diabetes, and Longevity: A 2-Sample Mendelian Randomization Study. Journal of Clinical Endocrinology & Metabolism, 2025;110(5):1451-1459.
- Lambe R, O’Grady B, Baldwin M, Doherty C. Investigating the accuracy of Apple Watch VO2 max measurements: A validation study. PLOS ONE, 2025;20(5):e0323741.
- Jurca R, Jackson AS, LaMonte MJ, et al. Assessing Cardiorespiratory Fitness Without Performing Exercise Testing. American Journal of Preventive Medicine, 2005;29(3):185-193.
- American College of Sports Medicine. ACSM’s Guidelines for Exercise Testing and Prescription, 11th ed., 2021 (Cooper Institute Aerobics Center Longitudinal Study normative data).
- Helgerud J, Høydal K, Wang E, et al. Aerobic High-Intensity Intervals Improve VO2max More Than Moderate Training. Medicine & Science in Sports & Exercise, 2007;39(4):665-671.