Zone 2 and VO2max: the two numbers that best predict your longevity

If you were to track only one health marker over the next twenty years, the available data points to cardiorespiratory fitness. A cohort study published in 2018 in JAMA Network Open, covering more than 120,000 patients who had undergone an exercise test, found a very strong relationship between cardiorespiratory fitness and all-cause mortality — with no plateau observed at high levels.

What VO2max actually measures

VO2max is the maximum volume of oxygen your body can take in, transport and use per minute, relative to your weight (ml/kg/min). It is an integrative indicator: it involves the lungs, the heart, the blood, the vessels and the capacity of muscle mitochondria to consume oxygen. When any one of those steps weakens, the number falls.

In practice it is also the measure of your functional reserve. Climbing four flights of stairs, running for a bus, surviving pneumonia at 75: all of it draws on the same reserve. It declines naturally by about 10 % per decade after thirty — and far faster with inactivity. The point of training is not only to raise the curve: it is to push to the right the moment it drops below the threshold of independence.

Zone 2: the base everything else depends on

Zone 2 is a low to moderate intensity, below the first ventilatory threshold: you can hold a conversation, you barely sweat, you feel you are “not working hard enough”. That is precisely where the most valuable adaptation happens.

At that intensity, muscle works mainly through slow fibres, very rich in mitochondria, and preferentially oxidises fatty acids. The training signal is twofold: an increase in the number and quality of mitochondria (mitochondrial biogenesis), and improved capillary density. The physiologist Iñigo San Millán did much to make this approach known among endurance athletes, before it was picked up in the longevity field, notably by the physician Peter Attia.

That ability to use fat at moderate intensity has a name: metabolic flexibility. It is degraded in metabolic syndrome and type 2 diabetes, and it is one of the mechanisms through which endurance training improves metabolic health independently of weight loss.

How to recognise zone 2 without equipment

• The talk test: you can say a complete sentence without catching your breath, but singing would be uncomfortable.
• Nasal breathing: you can still breathe through your nose alone, with effort.
• Feel: “I could keep this up for another hour” — 5 to 6 on a 10-point exertion scale.
• Heart rate: roughly 60 to 70 % of estimated max HR. A useful marker, but the estimating formulas have a margin of error of several beats.

The most common mistake by far: going too fast. Most amateur “easy” sessions are actually in zone 3 — too hard to build the base, too easy to develop VO2max. It is the grey zone that tires you without making you fitter.

Intervals: the direct lever on VO2max

To raise the ceiling, you have to go and touch it. Long high-intensity interval protocols — typically four repetitions of four minutes at high intensity, with three minutes of active recovery — are among the most studied for improving VO2max in untrained and trained subjects alike.

But those sessions are expensive in recovery terms. Hence the polarised model: about 80 % of volume at low intensity, 20 % at high, and almost nothing in between. It is the structure most endurance athletes use, and it also works for someone with four hours a week.

Brisk walking, cycling, rowing, swimming and the elliptical all work. Cycling has a practical advantage for zone 2: it is easier to hold a steady intensity than when running, where the slightest hill takes you out of the zone.

Tracking progress without a laboratory

A laboratory exercise test remains the reference measurement. At home, three indicators are more than enough to see progress:

• Heart rate at a fixed pace. If your HR falls for the same speed on the same route, you are progressing. It is the clearest signal.
• Speed at a fixed HR. The inverse of the above: you go faster for the same cardiac cost.
• Heart rate variability on waking. Measured with electrodes, as a seven-day trend. It reflects the state of the autonomic nervous system: a prolonged fall signals accumulated load, not rising fitness.

And a fourth, which everyone should track: resting blood pressure. High blood pressure is the leading modifiable risk factor for mortality worldwide, it is almost always symptomless, and having it checked costs nothing: most pharmacies take it for free, and your doctor records it at every consultation.

The four mistakes that cap progress

1. Doing everything in zone 3. Too hard for the base, too easy for the ceiling. Slow the easy sessions down, make the hard ones harder.
2. Neglecting strength. Aerobic capacity and muscle mass are two separate insurance policies. One does not replace the other: see our piece on muscle as a longevity organ.
3. Ignoring recovery. Adaptation happens between sessions. Degraded sleep cancels part of the benefit: that is the subject of our piece on the three systems of sleep.
4. Looking for the perfect plan. For a sedentary person, the biggest gain sits between zero and two sessions a week. Start there.

And supplements, in all this?

Honestly: marginal next to the training itself. Only three have a place in this context, and none replaces a session.

• Creatine improves performance on short intense efforts and supports muscle mass: useful for intervals and for strength.
• Electrolytes are genuinely useful beyond an hour of effort, in strong heat, or with heavy sweating. Below that, food is enough.
• Omega-3s act on the lipid profile, not on performance. It is a cardiovascular health intervention, not an ergogenic aid.

Everything else — fat burners, NO boosters, seven-stimulant “pre-workouts” — is marketing. In this field the hierarchy is clear: training volume, then sleep, then protein intake, then, a long way behind, supplements.