If I could order one test that would tell me more about a patient's long-term health trajectory than any other single measurement — labs included — it would be their VO2 max.
That's a strong claim. I want to back it up.
A landmark study published in JAMA Network Open in 2018 followed more than 120,000 adults who underwent exercise treadmill testing over more than two decades. The finding was striking: patients in the bottom quartile of cardiorespiratory fitness had five times the all-cause mortality risk of those in the top quartile. Not 20 percent higher risk. Not double. Five times.
That association was stronger than smoking. Stronger than hypertension. Stronger than diabetes. Stronger than any individual lab marker in our standard cardiovascular panel.
And it's modifiable. That's the part that matters most.
What VO2 Max Actually Measures
VO2 max — maximal oxygen uptake — is a measure of the maximum rate at which your body can consume oxygen during sustained intense exercise. It reflects the integrated efficiency of your cardiovascular system, your lungs, your blood's oxygen-carrying capacity, and your muscle cells' ability to extract and use that oxygen to produce energy.
The units are milliliters of oxygen per kilogram of body weight per minute — mL/kg/min. A higher number means your body can deliver and use more oxygen per unit of effort, which translates directly into greater cardiovascular reserve, better metabolic efficiency, and the physiological resilience to handle the demands of aging.
Think of it this way. Every physical demand in life — climbing stairs, carrying grandchildren, recovering from illness or surgery, managing the cardiovascular stress of an acute health event — draws on your cardiorespiratory reserve. VO2 max is a direct measure of how much of that reserve you have. More reserve means more margin. Less reserve means you're closer to the edge of what your body can handle.
The Marginal Decade — Why This Matters Now
At NOVA Wellness, our functional fitness assessment framework is built around what I call the marginal decade — the functional capacity required to maintain independence and quality of life at age 80 to 90.
Here is the challenge. VO2 max declines at approximately one percent per year after age 40, accelerating with each decade. That means a 50-year-old woman with a VO2 max of 30 mL/kg/min — which is average for her age — will have a VO2 max of roughly 20 by the time she reaches 80 if nothing changes. A VO2 max of 20 at 80 represents a very limited functional reserve — enough to walk slowly, but not enough to carry groceries up stairs, recover from a hospitalization quickly, or handle the demands of a full, active life.
The only way to arrive at 80 with adequate cardiorespiratory reserve is to build meaningfully above average now — while there is still time to build and while the body responds well to training. This is the same framework we apply to bone density, muscle mass, and every other physiological resource that declines with age. You cannot build it later. You build it now and maintain it.
Where You Should Be — By Age and Sex
Based on population data and the clinical targets I use in our functional fitness assessments, here is what the ranges look like:
Ages 40–49:
Elite (Grade A): ≥ 49 mL/kg/min for men · ≥ 43 for women
Above average (Grade B): 40–48 men · 34–42 women
Average (Grade C): 33–39 men · 27–33 women
Below average (Grade D): below 33 men · below 27 women
Ages 50–59:
Elite (Grade A): ≥ 43 mL/kg/min for men · ≥ 37 for women
Above average (Grade B): 34–42 men · 29–36 women
Average (Grade C): 28–33 men · 23–28 women
Below average (Grade D): below 28 men · below 23 women
The minimum longevity threshold — the floor I want every patient above — is the 75th percentile for their age. Average is not good enough if the goal is robust health in later decades. Average means half the population is doing better than you, and the decline curve from average puts you at risk of functional limitation well before the age most people expect it.
These numbers are not meant to be discouraging. They are meant to be honest — because knowing where you stand is the only way to do something about it.
How It Connects to Hormones and Metabolism
VO2 max and hormonal health are more connected than most people realize — and this is where the NOVA perspective adds something that a standard fitness assessment doesn't.
Testosterone directly influences VO2 max. Testosterone supports red blood cell production through erythropoiesis, improves mitochondrial function in muscle tissue, and supports the lean mass that drives cardiovascular efficiency. Men and women with low testosterone consistently show lower cardiorespiratory fitness for their age — and optimization of testosterone is associated with improvements in VO2 max over time. This is one of the reasons hormone therapy and exercise work synergistically rather than independently.
Thyroid function is similarly connected. Active thyroid hormone — Free T3 — directly regulates mitochondrial biogenesis and the efficiency of cellular energy production. Suboptimal thyroid conversion, as we covered in the thyroid post, is one of the most common reasons patients with apparently adequate training habits plateau at a VO2 max below where their effort should place them. The engine is capable; the fuel delivery is insufficient.
Insulin resistance reduces VO2 max through multiple mechanisms — impaired mitochondrial function, reduced glucose oxidation during exercise, and the metabolic inflexibility that prevents efficient fuel switching between fat and carbohydrate at different intensities. Improving insulin sensitivity — through resistance training, dietary modification, and when appropriate, GLP-1 therapy — consistently produces improvements in cardiorespiratory fitness alongside the metabolic benefits.
This is why VO2 max belongs in a comprehensive longevity evaluation alongside labs and body composition — not in a separate fitness assessment that never talks to the clinical picture.
Zone 2 Training — The Foundation
The most effective way to build VO2 max over time is not all-out sprints or high-intensity interval training — at least not primarily. The foundation is Zone 2 cardiovascular training.
Zone 2 is the exercise intensity at which you are working hard enough to elevate your heart rate meaningfully but still able to maintain a conversation in full sentences. It corresponds roughly to 65 to 75 percent of maximum heart rate and, more precisely, to a blood lactate level below 2.0 mmol/L — the upper threshold of aerobic metabolism before the body shifts into more anaerobic pathways.
Training at Zone 2 intensity for sustained periods — typically 30 to 60 minutes per session — builds mitochondrial density in muscle cells. More mitochondria means more capacity to generate energy aerobically, which directly raises the ceiling of what the cardiovascular system can do. This is the physiological basis of endurance improvement.
The practical talk test: during Zone 2 training you should be able to speak in complete sentences, but with mild effort — not comfortable conversation, not gasping. If you can sing, you're working too easily. If you can't speak in sentences, you've crossed into Zone 3 or above.
The research-backed minimum for meaningful VO2 max improvement is approximately 150 to 180 minutes of Zone 2 per week. This doesn't have to be running — brisk walking, cycling, rowing, swimming, or any sustained aerobic activity at the right intensity counts. The modality matters far less than the intensity and the consistency.
High-intensity intervals — true VO2 max efforts at 90 to 100 percent intensity — are a valuable addition once Zone 2 is established, and they produce more rapid short-term VO2 max improvements than Zone 2 alone. But without the aerobic base that Zone 2 builds, high-intensity training produces adaptation that fades quickly and doesn't translate to the long-term improvements we're after.
How to Test Your VO2 Max
The gold standard is a metabolic cart test — indirect calorimetry performed on a treadmill or cycle ergometer at a sports performance lab or cardiology facility. This is the most accurate measurement and the one that produces the numbers I use in clinical grading. It typically costs between $150 and $300 and takes about an hour including warm-up.
For patients who want a reasonable estimate without a formal test, modern fitness wearables — Garmin, Polar, and Apple Watch — use heart rate data during exercise to estimate VO2 max. These estimates are less precise than a metabolic cart test and vary in accuracy depending on the device and the individual, but they are useful for tracking trends over time and are reasonably reliable for patients who wear them consistently during aerobic activity.
A simpler field test: the Cooper 12-minute run. Run as far as possible in 12 minutes on a flat surface. Use a standard conversion formula to estimate VO2 max from the distance covered. It's not as precise as a metabolic cart, but it costs nothing and gives a reasonable ballpark.
What We Do with This at NOVA
VO2 max is part of our functional fitness assessment framework — the clinical grading system I've built to reverse-engineer from the marginal decade. Alongside strength, stability, mobility, body composition, and biomarker targets, cardiorespiratory fitness tells us what the patient's physiological runway looks like and what domains require the most urgent attention.
A patient with excellent labs and hormone optimization but a VO2 max in the bottom quartile is not in a good position long-term. The labs may be optimized. The cardiovascular reserve is not. We address both.
The goal is always the same: to help patients arrive at 80 with the reserves they need to do what matters to them. That requires starting now, building deliberately, and measuring progress honestly.
VO2 max is one of the most honest measurements we have. And it's one of the most responsive to the work you're willing to do.
If you want to understand where your cardiorespiratory fitness stands and what to do about it, that conversation starts with a consultation. Book a free 30 minutes at novawellnessut.com or call and text us at (801) 449-1402.
Matt Nelson, NP
NOVA Wellness — Orem, Utah
(801) 449-1402 · novawellnessut.com
