Why It Matters
VO2 max reflects how effectively your body captures, transports, and uses oxygen. Higher levels are associated with better functional capacity and lower risk of cardiovascular and all-cause mortality.
The key message is practical: fitness age can improve at any age. Even moderate increases in aerobic capacity can produce meaningful health and quality-of-life benefits.
What the Research Says
The clearest demonstration of VO₂ max's importance came from a 2018 study out of the Cleveland Clinic, led by Kyle Mandsager and published in JAMA Network Open. Researchers followed 122,007 patients who underwent treadmill exercise testing over a median of 8.4 years and found that cardiorespiratory fitness was inversely associated with all-cause mortality, with no observed upper limit of benefit — meaning fitness levels classified as "extreme" (two or more standard deviations above the mean for age and sex) were tied to the lowest risk-adjusted mortality of any group studied. In other words, there was no point at which being fitter stopped helping. Compare that to most health interventions, which tend to show diminishing returns or even reversals at the extreme end, and VO₂ max starts to look less like a nice-to-have fitness stat and more like a dose-dependent protective factor with no known ceiling.
That finding wasn't a fluke of one hospital's patient population. In 2022, Peter Kokkinos and colleagues published an analysis in the Journal of the American College of Cardiology examining cardiorespiratory fitness data from roughly 750,000 U.S. military veterans, spanning ages 30 to 95 and including large numbers of women and multiple racial groups. The study established age- and sex-specific fitness categories based on peak METs achieved during standardized treadmill testing and used Cox regression models to estimate mortality risk across those categories, confirming that the inverse relationship between fitness and all-cause mortality held consistently across the spectra of age, race, and sex. This matters because it rules out an obvious objection to the earlier data — that maybe the fitness-longevity link was really just a proxy for being young, male, or otherwise low-risk. It isn't. Higher fitness predicted better survival odds in septuagenarians and octogenarians just as reliably as it did in healthier, younger cohorts.
Given evidence at that scale, it's not surprising that the medical establishment has started treating fitness less like a lifestyle preference and more like a diagnostic. In 2016, the American Heart Association published a formal scientific statement, led by Robert Ross, arguing that cardiorespiratory fitness should be assessed as a routine clinical vital sign, alongside things like blood pressure and heart rate. The statement concluded that mounting evidence had firmly established low cardiorespiratory fitness as a risk factor for cardiovascular disease, all-cause mortality, and mortality from various cancers — putting it in the same category of seriousness as smoking or high blood pressure, despite VO₂ max rarely getting the same attention in a routine physical.
What makes this especially useful information, rather than just another statistic to feel anxious about, is that VO₂ max is one of the more directly modifiable numbers in the entire risk-factor conversation. You can't will your LDL cholesterol down through effort alone, and genetics play a real role in baseline fitness too, but structured aerobic training — particularly a mix of steady-state cardio and higher-intensity intervals — reliably raises VO₂ max at almost any age and starting point. The research above doesn't ask you to reach elite athlete status to benefit, either; the mortality curve drops sharply just moving out of the bottom quartile of fitness, meaning the biggest returns often come from the first meaningful improvements a previously sedentary person makes.
How to Apply It
You don't need a lab-based VO₂ max test to start acting on this information, though many gyms, sports medicine clinics, and some wearables now offer estimates. The more actionable takeaway is behavioral: build a regular mix of steady-state cardio (brisk walking, cycling, swimming) with occasional higher-intensity intervals, since both contribute to raising cardiorespiratory fitness over time. If you're currently sedentary, the research suggests you have the most to gain — simply moving out of the least-fit category tends to produce the sharpest drop in mortality risk of any step along the fitness spectrum.
Treat cardiorespiratory fitness the way you'd treat blood pressure or cholesterol: something worth knowing your number for, tracking over time, and actively working to improve, rather than an abstract "get more exercise" reminder. Few single numbers in health carry this much predictive weight while also being this trainable.
References
Association of Cardiorespiratory Fitness With Long-term Mortality Among Adults Undergoing Exercise Treadmill Testing. JAMA Network Open.Mandsager, K., Harb, S., Cremer, P., Phelan, D., Nissen, S. E., & Jaber, W. (2018, October 19).https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6324439/
Cardiorespiratory Fitness and Mortality Risk Across the Spectra of Age, Race, and Sex. Journal of the American College of Cardiology.Kokkinos, P., Faselis, C., Samuel, I. B. H., Pittaras, A., Doumas, M., Murphy, R., Heimall, M. S., Sui, X., Zhang, J., & Myers, J. (2022, August 9).https://www.jacc.org/doi/abs/10.1016/j.jacc.2022.05.031
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.Ross, R., Blair, S. N., Arena, R., Church, T. S., Després, J-P., Franklin, B. A., Haskell, W. L., Kaminsky, L. A., Levine, B. D., Lavie, C. J., Myers, J., Niebauer, J., Sallis, R., Sawada, S. S., Sui, X., & Wisløff, U. (2016, December 13).https://pubmed.ncbi.nlm.nih.gov/27881567/