Movement · 5 min
Zone 2: the longevity engine
In a study of over 122,000 adults, low cardiorespiratory fitness carried a higher mortality risk than smoking, diabetes, or established heart disease. Fitness is not a vanity metric. It is a signal of mitochondrial health, and mitochondria sit upstream of almost every chronic disease of ageing.
Why VO2max matters
VO2max — the maximum rate at which you can use oxygen — is a strong, dose-dependent predictor of all-cause mortality. Moving from the bottom 25% of fitness to merely above-average is associated with roughly a halving of mortality risk over the following decade. Moving from average to elite halves it again.
It is also one of the most modifiable markers in medicine. Most adults can add 15–20% to VO2max over a year of structured training.
What Zone 2 is
Zone 2 is the highest intensity at which you remain almost entirely aerobic — fat is the dominant fuel, lactate stays around 1.5–2 mmol/L, and you could, in principle, hold the effort for hours. Practically: a pace at which you can speak in full sentences but a conversation feels mildly inconvenient.
It is not slow because slow is virtuous. It is slow because mitochondrial biogenesis — the adaptation that makes you metabolically resilient — responds best to long, steady, sub-threshold work.
How to train it
Aim for 150–180 minutes per week of Zone 2, in sessions of 30–60 minutes. Walking uphill, cycling, rowing, easy running — anything that lets you sustain the effort. Add one shorter VO2max session per week (4 × 4 minutes hard with 4 minutes recovery is the classical protocol). Keep two resistance sessions on top.
What to do this week
- Schedule three 45-minute Zone 2 sessions. Talk-test pace, no faster.
- Add one VO2max interval session: 4 × 4 minutes hard, 4 minutes easy.
- Keep two resistance training sessions — strength and aerobic fitness are independent longevity inputs.
- If you train by heart rate, a rough Zone 2 ceiling is 180 minus your age (individual variation is large; lactate or talk test is better).