Zone 2 Training
Build more mitochondria. Burn more fat. Live longer.
Objective
Accumulate 3-4 hours per week of low-intensity aerobic training to build mitochondrial density and metabolic flexibility. Zone 2 is the intensity where fat oxidation is maximized and lactate remains stable (San-Millán & Brooks, 2018).
Both San Millán and Seiler agree: ~80% of training volume should be Zone 2 (San-Millán & Brooks, 2018; Seiler, 2010). Elite endurance athletes know this. Most recreational exercisers don’t.
Key benefits:
- More mitochondria = more cellular energy capacity
- Better lactate clearance = higher ceiling for intense work later
- Improved insulin sensitivity = better metabolic health (Attia, 2023)
The Protocol
How to find Zone 2:
- Talk Test (best): Can hold a conversation, but would rather not. Can’t sing.
- RPE: 3-4 out of 10. Feels easy. Sustainable for hours.
- Heart Rate: 70-80% max HR, or 180 minus age. HR is noisy—trust the talk test first.
Session structure:
- 5 min warmup at easy pace
- 45-90 min at Zone 2 intensity
- 5 min cooldown
Best modalities:
- Stationary bike / trainer (easiest to control intensity)
- Incline walking / rucking
- Rowing (if technique allows low HR)
- Running (often spikes HR too high for beginners—use caution)
Cadence
- Weekly: 3-4 sessions, 45-90 min each
- Monthly: Review average watts/speed at target HR
- Quarterly: Retest Zone 2 threshold (should improve)
Time tradeoffs: 3×45 min beats 2×60 min. More frequency > longer sessions.
KPIs
| Indicator | Type | Target | How to measure |
|---|---|---|---|
| Sessions/week | Leading | ≥3 | Training log |
| Total weekly minutes | Leading | 150-240 min | Training log |
| Watts/speed at Zone 2 HR | Lagging | Increasing over months | Compare same HR, higher output |
| Resting heart rate | Lagging | Decreasing trend | Morning measurement |
Failure Modes
| Problem | Fix |
|---|---|
| Drifting into Zone 3 | Feels productive but isn’t; too hard for mitochondria, too easy for VO2max. Slow down. |
| Boredom | Audiobooks, podcasts, or TV. The benefit is cellular, not psychological. |
| HR spikes on runs | Switch to bike or incline walk until aerobic base improves |
| Skipping sessions | Schedule like meetings; pair with entertainment you enjoy |
| No time for 60+ min | 3×30 min still helps; consistency > duration |
Progression
Don’t increase intensity. Zone 2 is a biological state, not a performance target.
Progress by increasing the wattage or speed required to stay in Zone 2. That’s fitness improving.
Related
- Dependency: Optimize_Sleep (recovery and adaptation happen during sleep)
- Complement: Train_Strength (the other 20% of the training equation)
- Concept: Cardio_vs_Strength (why both matter)