Five years ago, Zone 2 training was something only elite endurance coaches discussed in hushed tones. Today, everyone from longevity researchers to weekend warriors seems to be evangelising it. But what does the science actually say — and are you doing it right?
At SOMA, we've seen a 340% increase in Zone 2 training logs over the past 18 months. Here's everything you need to know to do it correctly.
What is Zone 2?
Zone 2 refers to a specific intensity band of aerobic exercise, typically defined as 60–70% of your maximum heart rate — the effort level at which you can hold a conversation but feel a slight challenge doing so. More precisely, Zone 2 is the highest intensity at which your body primarily burns fat as fuel and clears lactate at the rate it's being produced, keeping blood lactate below approximately 2 mmol/L.
It's harder than a walk, easier than you might think, and deceptively powerful.
The physiology: why Zone 2 is special
The benefits of Zone 2 training operate primarily at the cellular level, which is why they've been largely invisible to traditional performance tracking.
Mitochondrial biogenesis. Zone 2 is the most potent known stimulus for increasing mitochondrial density and efficiency. Research from Dr. Iñigo San Millán's lab at CU Boulder found that elite cyclists have approximately 3–5× more mitochondrial capacity per gram of muscle than sedentary individuals — and Zone 2 training is the primary driver of this adaptation.
Fat oxidation capacity. Modern lifestyles and high-intensity training dominance have eroded many athletes' ability to burn fat efficiently. Zone 2 reverses this. Over 8–12 weeks, regular sessions dramatically improve your fat oxidation rate — you sustain higher intensities before depleting glycogen, and recover faster because your aerobic system is more efficient.
Cardiac output. Consistent aerobic base work increases stroke volume (blood pumped per heartbeat) and lowers resting heart rate — two of the most reliable markers of cardiovascular fitness and long-term health.
How much Zone 2 do you need?
Elite endurance athletes typically spend 75–80% of their total training volume in Zone 2. For recreational athletes and those in non-endurance sports, the evidence supports a minimum of 150 minutes per week, with 200–300 minutes per week producing the most significant adaptations.
The most common mistake SOMA users make? Going too hard. Without precise heart rate zone calibration, most people naturally gravitate toward Zone 3 — the "grey zone" — which is harder on the body, less metabolically specific, and substantially slower to produce Zone 2 adaptations.
How SOMA prescribes your Zone 2
Your Zone 2 heart rate range is highly individual — it cannot be accurately derived from generic age-based formulas. SOMA calculates your personalised zones using:
Critically, SOMA adjusts Zone 2 prescriptions based on your daily Readiness Score. On high-suppression days, a Zone 2 session may be recommended as active recovery — at a slightly lower intensity and shorter duration than your progressive training sessions.
The Zone 2 protocol for beginners
Weeks 1–2: 3 × 30-minute sessions at true Zone 2 intensity (nasal breathing, conversational). Focus on keeping your heart rate in zone — not on pace or speed.
Weeks 3–4: Progress to 3 × 40 minutes, plus one 60-minute session on a weekend.
Month 2: Target 3–4 sessions per week totalling 150–180 minutes.
Month 3+: Increase weekly volume by no more than 10% per week toward 200–300 minutes.
Expect to feel surprisingly slow at first — particularly if you're accustomed to high-intensity training. Embrace it. The adaptations are happening beneath the surface.
Measuring progress
Zone 2 progress is best measured not by speed, but by how fast you can go at the same heart rate. After 8–12 weeks, SOMA users typically see their aerobic threshold pace improve by 10–20% — meaning significantly faster movement while keeping heart rate firmly in Zone 2.
That's your mitochondria at work. And they're telling you the protocol is working.