Zone 2 vs Zone 3: what's the difference?
Zone 2 is easy, conversational running that builds your aerobic base. Zone 3 is moderate, "comfortably hard" running that feels productive but adds more fatigue. Most recreational runners spend too much time in Zone 3 and not enough in Zone 2.
| Zone 2 | Zone 3 | |
|---|---|---|
| Heart rate | ~60–70% of heart rate reserve | ~70–80% of heart rate reserve |
| How it feels | Easy, full sentences | Moderate, short phrases |
| Trains | Aerobic base, fat use, efficiency | Tempo endurance |
| Recovery cost | Low | Medium |
| How often | Most of your runs | Occasionally, as planned workouts |
Find your exact ranges with the calculator.
Why Zone 3 is the trap
Zone 3 feels like a good workout, so it's where runners drift when they run "by feel." But doing it every day leaves you too tired to run truly hard on hard days and too fatigued to recover. That's how runners plateau, a pattern often called the "gray zone."
When Zone 3 helps
- Tempo runs: 20 minutes comfortably hard, once a week, for runners with a solid base.
- Race-pace practice for half marathons and marathons.
The fix
Keep your easy days truly easy (Zone 2), keep your hard days purposeful, and aim for roughly 80% easy overall.
Stay out of the gray zone
RunZone tells you in your ear when you drift out of Zone 2 on easy days, so your easy runs stay easy.
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Is Zone 3 bad?
No. Zone 3 has a place, like tempo runs or races. The problem is doing almost every run there, because it adds fatigue without the full benefits of either easy or hard training.
How do I know if I'm in Zone 3 instead of Zone 2?
In Zone 3 you can speak in short phrases, not full sentences. In Zone 2 you can hold a conversation.
How much Zone 3 should I do?
Most plans keep the large majority of running easy, with harder work, including Zone 3 tempo, making up roughly 20% or less.