VO2 max is probably one of the topics I’ve written about most. And hopefully, I’ve not beaten a dead horse here. I just think there’s endless interest in it, and I don’t think it’s the “fad” people make it out to be.
Even though the importance of VO2 max has been underscored by me and others on numerous occasions, it has resurfaced in the mainstream conversation for a different reason—people are questioning its validity as a true “longevity biomarker.” Because of that, I felt like it would be nice to provide a “state-of-the-science” update.
I’ve been doing the podcast rounds lately, which has allowed me to brush up on research on VO2 max as a longevity biomarker. That’s what this post is about, plus the most up-to-date research on how to improve it with training and other tactics. If you want a somewhat deeper dive into the science, you can pick up my book “VO2 Max Essentials” on Amazon.
Why VO2 max still matters
VO2 max remains one of the most discussed metrics in exercise physiology, and for good reason. It is the maximum rate at which the body can take up, transport, and utilize oxygen during intense exercise and is widely regarded as the gold-standard laboratory measure of cardiorespiratory fitness (CRF). The American Heart Association reinforced the clinical importance of CRF in their latest update, arguing that it should be routinely assessed in healthcare and even framing it as a clinical vital sign.
That said, VO2 max is often discussed too loosely. It is not a standalone “longevity score,” and it is not interchangeable with every estimate of aerobic fitness produced by a treadmill test, population equation, or (especially) wearable. It is a specific physiological construct that we should interpret with nuance.
What VO2 max actually reflects
Physiologically, VO2 max is best understood as an integrative property of the oxygen transport system. It depends on pulmonary gas exchange, cardiac output, blood oxygen-carrying capacity, the distribution of blood flow, and the ability of working muscles to extract and use oxygen. It reflects how well the body can deliver and utilize oxygen when the demand for aerobic energy production is at its highest (e.g., during maximal exercise).
That systems-level nature is, in my opinion, what makes VO2 max so compelling.
It is not simply a marker of “cardio” in the casual sense. It is a summary readout of how multiple organ systems perform together under stress. At the same time, it does not fully determine endurance performance on its own. Endurance outcomes also depend heavily on economy, durability, and the fraction of VO2 max that can be sustained near threshold, hence why the guy or girl with the highest VO2 max doesn’t always win the race.
Where the longevity evidence is strongest
There’s no question that a higher level of fitness is associated with a lower risk of dying.
A 2024 overview of meta-analyses synthesized 26 systematic reviews representing 199 unique cohort studies and more than 20.9 million observations.1Lang, J. J., Prince, S. A., Merucci, K., Cadenas-Sanchez, C., Chaput, J.-P., Fraser, B. J., Manyanga, T., McGrath, R., Ortega, F. B., Singh, B., & Tomkinson, G. R. (2024). Cardiorespiratory fitness is a strong and consistent predictor of morbidity and mortality among adults: an overview of meta-analyses representing over 20.9 million observations from 199 unique cohort studies. British Journal of Sports Medicine, 58(10), bjsports-2023-107849. https://doi.org/10.1136/bjsports-2023-107849
- Across those data, higher CRF was strongly and consistently associated with lower all-cause mortality, lower cardiovascular mortality, and lower risk of several chronic disease outcomes.
- High versus low CRF was associated with a 53% reduction in all-cause mortality risk, and each 1-MET (3.5 ml/kg/min of oxygen uptake) was associated with a 11% to 17% lower risk of all-cause mortality, depending on the meta-analysis.
Those are impressive associations, but the certainty should not be overstated. The same overview rated the certainty of evidence across outcomes from very low to moderate. That does not weaken the overall signal, which is clearly strong and consistent, but it does warrant caution when translating these epidemiologic associations into sweeping mechanistic claims. And I should note that many studies here were not actually about directly measured VO2 max. They are about CRF more broadly. So let’s discuss that…
VO2 max and CRF are related, but they are not interchangeable
A recent source of controversy is not whether aerobic fitness is important, but whether VO2 max is a useful, meaningful marker worth measuring (separately from CRF, that is).
This arose because many of the most-cited mortality studies do not rely on direct breath-by-breath laboratory measurements of VO2 max. Instead, they often use objectively measured exercise capacity expressed in METs, treadmill-estimated CRF, or even non-exercise CRF estimation models.
How much does that matter? Maybe not much if we’re talking about the strength of associations.
A 2025 systematic review and meta-analysis of 42 studies representing 35 cohorts and 3.8 million observations found:2Singh, B., Cadenas-Sanchez, C., Bruno, José Castro-Piñero, Chaput, J.-P., Cuenca-García, M., Maher, C., Nuria Marín-Jiménez, McGrath, R., Molina-Garcí, P., Myers, J., Gower, B., Ortega, F. B., Lang, J. J., & Tomkinson, G. R. (2024). Comparison of objectively measured and estimated cardiorespiratory fitness to predict all-cause and cardiovascular disease mortality in adults: A systematic review and meta-analysis of 42 studies representing 35 cohorts and 3.8 million observations. Journal of Sport and Health Science/Journal of Sport and Health Science, 100986–100986. https://doi.org/10.1016/j.jshs.2024.100986
- Objectively measured and estimated CRF showed broadly similar dose-response associations with all-cause and cardiovascular mortality.
- For each 1-MET increase in CRF, all-cause and cardiovascular mortality decreased by 14% and 16%, respectively, with no statistically significant differences between the objective and estimated approaches.
That is important because it supports the broader conclusion that fitness is a powerful risk marker, regardless of how it’s measured. Nevertheless, the epidemiology is strongest for CRF as a construct. VO2 max is the gold-standard laboratory expression of that construct, but the two are not perfectly synonymous in the literature. I’m willing to accept that, but I’m not quite convinced the semantics matter if we’re talking about longevity in the general sense.
Is VO2 max a biomarker?
Whether VO2 max should be called a biomarker depends largely on how the term is being used. If the intended meaning is an objective, reproducible measure associated with future health outcomes, then VO2 max or CRF clearly behaves like one.
If the intended meaning is a singular mechanistic readout of biological aging, the label becomes much harder to defend. The American Heart Association’s framing is more conservative and more useful: CRF is a vital sign because it provides meaningful prognostic information that improves risk assessment and clinical management. That is, it tells you more about your health when paired with common cardiovascular disease biomarkers (and probably more than any single risk factor, such as cholesterol, blood glucose, or whether you smoke).
I think the most defensible description is that VO2 max is an integrative functional marker. It compresses a great deal of physiology into one number, but it does not function like a magic molecular biomarker that fully explains why one person lives longer or ages better than another.
How to reliably improve VO2 max
If the goal is to improve VO2 max, the broad evidence still supports the straightforward (and boring) answer: combine sufficient aerobic volume with some strategically dosed high-intensity training.
A 2024 umbrella review of 24 systematic reviews, 429 primary studies, and 12,967 participants concluded that high-intensity interval training (HIIT) improves CRF compared with both non-exercise controls and moderate-intensity continuous training. Across included reviews, the average difference versus moderate-intensity continuous training ranged from 0.52 to 3.76 mL/kg/min.3Poon, E. T.-C., Li, H.-Y., Gibala, M. J., Wong, S. H.-S., & Ho, R. S.-T. (2024). High-intensity interval training and cardiorespiratory fitness in adults: An umbrella review of systematic reviews and meta-analyses. Scandinavian Journal of Medicine & Science in Sports, 34(5), e14652. https://doi.org/10.1111/sms.14652
So while the evidence supports HIIT as an effective and often time-efficient way to improve CRF, it does not mean every interval protocol is equally effective, or that interval work should be treated as the entire training story. Higher-intensity work is a useful tool for improving VO2 max, especially when it is programmed well and layered onto an adequate aerobic foundation.
Low intensity still matters
Low-intensity endurance training is sometimes dismissed as secondary or overly romanticized as “zone 2.” The evidence supports neither extreme—training performed below the first lactate or ventilatory threshold (the typical “zone 2” range) has been shown to produce a large effect on relative VO2 max and to improve several cardiometabolic risk factors. In the same meta-analysis, higher exercise intensity was associated with greater gains in VO2 max, but low-intensity training alone still meaningfully improved aerobic fitness.
That is probably the most useful way to frame low-intensity training. It is not a magical intensity zone. It is a practical way to accumulate enough recoverable volume to support aerobic adaptation. For most people, it makes more sense to think of low intensity as the foundation and high intensity as a potent but limited tool layered on top.
Polarized versus pyramidal distribution
Training intensity distribution—essentially how much of one’s training is spent in the various training zones—is another area where strong opinions often outrun the evidence.
A 2025 systematic review and meta-analysis in endurance athletes found no significant overall difference between polarized (a model that focuses on an 80/20 split between low- and high-intensity training with little emphasis on more moderate intensities) and pyramidal training (a model that emphasises high-volume low-intensity, moderate-volume “zone 2” intensity, and little high-intensity training) distributions for improving VO2 max or time-trial performance, although subgroup analyses did suggest that competitive athletes may benefit more from polarized models while recreational athletes may respond well to pyramidal ones.4Rosenblat, M. A., Watt, J. A., Arnold, J. I., Treff, G., Sandbakk, Ø. B., Esteve-Lanao, J., Festa, L., Filipas, L., Galloway, S. D., Muñoz, I., Ramos-Campo, D. J., Schneeweiss, P., Sellés-Pérez, S., Stöggl, T., Talsnes, R. K., Zinner, C., & Seiler, S. (2025). Which Training Intensity Distribution Intervention will Produce the Greatest Improvements in Maximal Oxygen Uptake and Time-Trial Performance in Endurance Athletes? A Systematic Review and Network Meta-analysis of Individual Participant Data. Sports Medicine (Auckland, N.Z.), 10.1007/s40279-02402149-3. https://doi.org/10.1007/s40279-024-02149-3
That doesn’t mean distribution is irrelevant. It means that the evidence does not support claims that one model universally wins. Successful endurance training tends to be low-intensity dominant, while the optimal mix of moderate and high intensity likely depends on training status, event demands, and the rest of the program. In other words, do what works for you.
What to make of sauna, ketones, and other adjuncts
One area I’m particularly interested in is the science of “hacking” VO2 max. What can you add to training that will effectively improve your fitness above and beyond the exercise stimulus? Here are a few I’ve covered lately (in my newsletter or elsewhere):
Passive heat exposure
Passive heat exposure after training is a good example where the data are interesting but inconclusive.
A 2025 systematic review and meta-analysis found trivial effects of post-exercise heat exposure on endurance performance in both hot and thermoneutral conditions, with only small effects on VO2 max and some physiological outcomes. That makes sauna or hot-water immersion an interesting adjunct, but not a first-line strategy for improving VO2 max.5Thomas, & Laye, M. J. (2025). The effect of post-exercise heat exposure (passive heat acclimation) on endurance exercise performance: a systematic review and meta-analysis. BMC Sports Science Medicine and Rehabilitation, 17(1). https://doi.org/10.1186/s13102-024-01038-6
There are some individual studies that have caught my eye, though. One that I recently wrote about found that passive heat after training, specifically repeated hot-water immersion, appeared to improve VO2 max in already well-trained runners without changing their normal training load.6Holmer, B. (2025, December 12). Physiology Friday #297: Post-Workout Hot Baths Provide a VO2max Boost. Physiologicallyspeaking.com; Physiologically Speaking. https://www.physiologicallyspeaking.com/p/physiology-friday-297-post-workout
- Runners completed a 5-week hot-water immersion block and a matched control block in a crossover design.
- The hot-water protocol was 45 minutes, 5 times per week, at a temperature of at least 104℉/40°C, usually after normal runs.
- The hot-bath phase increased VO2 max by 2.7 mL/kg/min.
- It also increased hemoglobin mass by 33 g, blood volume by 284 mL, and left ventricular end-diastolic volume by 10 mL, suggesting the gains were driven by both improved oxygen-carrying capacity and a heart that could fill and pump more blood per beat.
Post-exercise ketones
Ketone supplementation is another area where the evidence base remains a bit less mature than the marketing… but where studies and excitement are accumulating. It’s also an area where I’m personally experimenting (I use a serving or two of ketone-IQ ketones after most of my long or hard workouts).
A recent 2026 trial (that I covered in my newsletter) found that post-exercise ketone ester supplementation during an 8-week supervised endurance training program increased relative VO2 peak more than in the control group and improved 30-minute time-trial performance in trained men, apparently through peripheral muscular adaptations rather than greater peak cardiac output. That result is interesting and worth following, but it remains a single recent trial in a narrow population.
Exercise snacks
One adjunct strategy that may be more relevant for public health than for performance optimization is the idea of “exercise snacks”—short, intermittent bouts of activity performed throughout the day.
A 2026 systematic review and meta-analysis found that brief structured bouts of exercise lasting 5 minutes or less, performed at least twice daily, significantly improved CRF in physically inactive adults (emphasis on inactive). These are not a substitute for structured endurance training, but they are a plausible, evidence-based strategy for improving fitness in largely sedentary populations.7Rodríguez, M. Á., Quintana-Cepedal, M., Cheval, B., Thøgersen-Ntoumani, C., Crespo, I., & Olmedillas, H. (2025). Effect of exercise snacks on fitness and cardiometabolic health in physically inactive individuals: systematic review and meta-analysis. British Journal of Sports Medicine, bjsports-2025-110027. https://doi.org/10.1136/bjsports-2025-110027
However, I think exercise snacks can also have utility for the average fit person who’s training quite a bit—a way to “sneak in” some extra strength or aerobic work on top of a strong foundation. I use them all the time.
The latest evidence does not diminish the importance of VO2 max. If anything, it reinforces its value.
Cardiorespiratory fitness remains one of the strongest predictors of morbidity and mortality, and VO2 max is the gold-standard laboratory measure of this broader trait. But the science also argues for some precision and nuance. To recap:
- The strongest epidemiology is about CRF broadly, not always directly measured VO2 max.
- The best evidence for intervention still favors a combination of substantial aerobic work and some well-targeted high-intensity training.
- Most of the “hacks” around VO2 max remain adjuncts at best (but that doesn’t diminish their utility).
A science-forward view of VO2 max is therefore not that it is overrated. It is that it is best understood as a powerful systems-level marker—useful, informative, and worth improving.
