VO2max and Zone 2 training: the key longevity biomarker

VO2max is the maximum amount of oxygen your body can take in, transport and use during maximal effort. Expressed in ml/kg/min, it is the gold standard for cardiorespiratory fitness.

The value reflects the entire oxygen cascade: pulmonary ventilation, cardiac output, oxygen transport in the blood and the mitochondrial capacity of your muscles. A high VO2max signals more than sporting ability. It points to efficient physiology right down to cellular level.

The Fick equation describes what sits behind it: VO2max = maximum heart rate × maximum stroke volume × arteriovenous oxygen difference. All three components can improve. That is exactly where targeted training comes in.

The scientific picture is clear: cardiorespiratory fitness, measured as VO2max, is among the strongest predictors of all-cause mortality, comparable to or stronger than classic risk factors such as smoking or high blood pressure. Three large cohort studies involving more than 975,000 participants shaped this field.

The Cleveland Clinic study (Mandsager 2018) analysed 122,007 patients across 1.1 million person-years. The result: there is no upper limit to the benefit. Even the fittest participants still did better than the next-fittest group. Low fitness was associated with a 3.5-fold higher risk of death than smoking.

The largest study to date (Kokkinos 2022, 750,302 veterans) confirmed that low fitness is more dangerous than any cardiac risk factor examined. The association was inverse, independent and graded across all age groups, both sexes and all ethnic groups.

This part is especially relevant: your starting value is not the whole story. Every improvement of 1 ml/kg/min VO2max was associated with 9% lower all-cause mortality, regardless of where people started. Even a moderate gain of just 1 MET between two exercise tests was linked to significantly lower mortality.

VO2max peaks in the early to mid-20s and then declines continuously: an average of 10% per decade in adults aged 20 to 65. From age 70, the decline accelerates to 15–20% per decade.

The key distinction is between unavoidable biological ageing and preventable decline caused by behaviour. Reviews estimate that 50–70% of the decline in VO2max can be prevented through consistent training. Biology sets the slope. Your behaviour decides how steep the drop becomes.

Physiological causes include a maximum heart rate that falls by 5–10 beats per decade, lower mitochondrial efficiency, reduced muscle capillary density and loss of muscle mass (sarcopenia).

Zone 2 training means working at moderate intensity that mainly taxes the aerobic energy system. It sits below the first lactate threshold (LT1) and feels "comfortably hard": you can still just about speak in sentences, but you can no longer sing comfortably.

Here is the crucial point. Zone 2 is not effortless cruising. It is the intensity that most strongly stimulates your mitochondria and oxidative capacity without tipping into the anaerobic range. Iñigo San Millán, professor at the University of Colorado and coach to Tour de France riders, describes Zone 2 as deliberate metabolic stimulation.

One caveat. A 2025 study found substantial individual variation in Zone 2 markers. Standard percentages of HRmax do not reflect everyone's actual metabolic demands. Lactate measurement remains the most accurate proxy.

Zone 2 training works on several levels at once. That breadth is what makes it so valuable for longevity.

Mitochondrial biogenesis: your body builds new mitochondria. The transcription factor PGC-1α, the "master regulator" of mitochondrial biogenesis, is activated. Sessions of 60–90 minutes trigger a stronger response than 30-minute sessions.

Fat oxidation and metabolic flexibility: Zone 2 teaches your body to use fat more efficiently as fuel. Insulin sensitivity improves, blood sugar regulation becomes more stable and you depend less on carbohydrates.

Cardiovascular adaptations: stroke volume rises, capillary density in the muscles increases, resting heart rate and blood pressure fall, and endothelial function improves.

Lactate clearance: lactate moves from fast-twitch to slow-twitch fibres, where it is burned as fuel. MCT transporters are upregulated. Lower lactate at the same workload means better metabolic health.

Not ideal if raising VO2max is your only goal: a 2025 narrative review found that Zone 2 on its own is not the optimal intensity for mitochondrial adaptations, because higher intensities trigger stronger PGC-1α responses. Zone 2 is therefore recommended as a base combined with high-intensity training. Its strength is volume tolerance. You can train for far more hours in Zone 2 than with HIIT without overloading yourself.

The best-supported training concept for longevity right now is the polarised method: roughly 80% Zone 2 and 20% Zone 5. Peter Attia sums it up: "Life is Zone 1, Zone 2, and Zone 5."

A randomised controlled trial in untrained adults backs this up: polarised training improved VO2max by 12.9%, more than HIIT alone (9.8%) or threshold training (7.3%). Zone 2 builds the "floor" (aerobic base). Zone 5 raises the "ceiling" (maximum capacity).

Gold standard: spiroergometry. Cardiopulmonary exercise testing (CPET) measures your oxygen consumption through a mask while the workload rises in stages. It is the most accurate option and also identifies the VT1 and VT2 thresholds. Sports-medicine centres offer it, and prices vary by country and provider.

Submaximal tests: the Cooper test (12-minute run), the beep test (shuttle run) or a graded ergometer test give useful estimates without an all-out effort.

Smartwatch estimates: Apple Watch, Garmin and COROS estimate VO2max from heart rate, pace and movement data. They can be 5–10 ml/kg/min off laboratory values. As a trend indicator (getting better or worse?), they are still useful.

Use our heart-rate zone calculator to work out your personal training zones.

Finding Zone 2 without a lab:

• Talk test: full sentences are possible, singing is not
• Nose test: you can only just breathe through your nose alone
• Heart rate: 60–70% of HRmax (rule of thumb: 220 minus your age)
• Subjective effort: RPE 3–4 out of 10, challenging but repeatable
• Lactate: 1.5–2.0 mmol/L, if you have a meter