In thirty years of clinical practice, I have never found a single number more predictive of long-term health outcomes than cardiorespiratory fitness, specifically VO₂ max. Not cholesterol. Not fasting glucose. Not even blood pressure. When researchers from the Cleveland Clinic followed over 122,000 patients, they found that low cardiorespiratory fitness carried a higher mortality risk than hypertension, smoking, diabetes, or end-stage renal disease combined.
Let that land for a moment. We spend enormous energy treating blood pressure and managing lipid panels, yet the most potent prognostic tool we have is a measure most annual physicals do not even order.
"Low cardiorespiratory fitness is the strongest predictor of all-cause mortality we have, stronger than smoking, stronger than hypertension, stronger than diabetes."
Cleveland Clinic, JAMA Network Open, 2018
What VO₂ Max Actually Measures
VO₂ max is the maximum rate at which your body can consume oxygen during maximal exertion. It is expressed in millilitres of oxygen per kilogram of body weight per minute (mL/kg/min). At its core, it is a measure of how efficiently your cardiovascular and respiratory systems can deliver and utilise oxygen: the fuel for everything your cells do.
A 40-year-old man with a VO₂ max above 50 mL/kg/min sits in the "Superior" category. The average sedentary 40-year-old sits around 35. Elite endurance athletes routinely exceed 70. What matters for our purposes is not the elite end. It is the mortality cliff at the low end. Moving from the lowest fitness quintile to the second-lowest is associated with a greater reduction in all-cause mortality than moving from the second-highest to the highest.
Why It Predicts So Much More Than Heart Disease
The instinct is to frame VO₂ max as a cardiovascular metric. It is, but only in part. What it actually captures is the integrated efficiency of multiple systems simultaneously: cardiac output, lung diffusion capacity, blood oxygen-carrying capacity, mitochondrial density in muscle tissue, and the vascular network's ability to deliver that oxygen to working cells.
This is why VO₂ max predicts not just cardiovascular mortality, but cancer outcomes, cognitive decline, and all-cause mortality. Many of the biological mechanisms that drive chronic disease (mitochondrial dysfunction, oxidative stress, inflammatory burden) are also the mechanisms that depress aerobic fitness. VO₂ max is a proxy for systemic biological age in a way that few other single measurements can match.
VO₂ max can be measured directly via a maximal exercise test with metabolic cart (gold standard) or estimated via submaximal protocols. At Ultra Healthy Human, we use a calibrated submaximal treadmill protocol that correlates closely with direct measurement and is appropriate for most clinical patients.
The Decline Problem and the Intervention Window
Without deliberate intervention, VO₂ max declines approximately 10% per decade from early adulthood. By age 70, a sedentary individual may have lost 40–50% of the aerobic capacity they had at 25. This matters because the absolute value at any given age is a function of both your peak and the rate of decline, and we can influence both.
The window for meaningful intervention is not a brief one. We see significant VO₂ max improvements in patients well into their 60s and 70s with appropriately structured training. The ceiling rises more slowly with age, but the mortality benefit of each unit improvement is, if anything, greater in older patients because they are starting from closer to the threshold where risk escalates sharply.
How to Actually Move the Number
The research is unambiguous that the most efficient way to increase VO₂ max is high-intensity interval training, specifically intervals at or near VO₂ max intensity. The Norwegian 4×4 protocol, developed and validated by researchers at the Norwegian University of Science and Technology, produces the most consistent results in the literature: four intervals of four minutes each at 85–95% of maximum heart rate, separated by three-minute active recovery periods, performed twice weekly.
Get a VO₂ max test, either direct or estimated. Without a starting point, you cannot track progress or calibrate training intensity correctly.
Use the Norwegian 4×4 protocol as your anchor. This is the most evidence-supported approach for VO₂ max improvement across all age groups.
Zone 2 training (sustained moderate-intensity effort where you can still hold a conversation) builds mitochondrial density and supports the adaptations that HIIT demands.
VO₂ max adaptations accumulate over months, not weeks. Retest quarterly to track progress and adjust intensity targets as fitness improves.
What We Track at Ultra Healthy Human
Every new patient at Ultra Healthy Human receives a baseline cardiorespiratory fitness assessment as part of their initial workup. We use age- and sex-adjusted norms to contextualise the result, and we set a personalised target VO₂ max based on where the patient wants to be, not just relative to their age cohort, but relative to the biological age they are aiming to maintain.
For patients who want to go deeper, we pair the VO₂ max assessment with a full metabolic panel that includes fasting insulin, HSCRP, homocysteine, and our expanded lipid panel. Together, these give us a comprehensive picture of where cardiovascular and metabolic risk actually sits, and what to do about it.
Know your number
A VO₂ max assessment is part of every Ultra Healthy Human initial workup. If you do not know your cardiorespiratory fitness level, schedule a consultation and we will establish your baseline, and build a protocol to move it.