What Are Heart Rate Zones?
Heart rate zones divide your heart rate range into five distinct training intensities — from very easy recovery efforts all the way to maximum sprint work. Training with zones lets you match your effort level to your goal, rather than just "going hard" every session.
Each zone triggers a different physiological response. Understanding them turns guesswork into a real training strategy.
The Five Zones
### Zone 1 — Recovery (50–60% of max HR)
This is gentle movement. Walking, easy cycling, or a slow jog. Your body primarily uses fat for fuel, and your cardiovascular system gets a break. Zone 1 is ideal for active recovery days between harder sessions.
### Zone 2 — Fat Burn / Aerobic Base (60–70% of max HR)
Zone 2 is where most of your long-distance base training should happen. It feels comfortable — you can hold a full conversation. Your body is efficiently burning fat as its primary fuel source, and you're building mitochondrial density, which is the engine of aerobic fitness. Many elite endurance athletes spend 80% of their training here.
### Zone 3 — Cardio / Aerobic (70–80% of max HR)
This is a moderate aerobic effort — comfortably uncomfortable. Zone 3 improves cardiovascular efficiency and is the classic "cardio" zone. Good for tempo runs, cycling at a steady pace, or sustained swimming efforts.
### Zone 4 — Hard / Threshold (80–90% of max HR)
At Zone 4, you're working near your lactate threshold — the point at which lactic acid begins to accumulate faster than your body can clear it. Training here increases your threshold, meaning you can sustain higher efforts before fatiguing. Interval training and tempo workouts typically target this zone.
### Zone 5 — Peak / VO2 Max (90–100% of max HR)
This is maximum effort. Short, intense bursts — sprints, HIIT finishers, or all-out hill repeats. Zone 5 develops raw speed and raises your VO2 max ceiling. You can only sustain this for seconds to a few minutes.
Why Training With Zones Works
Random effort leads to random results. Zones give you precision:
- Aerobic base days stay in Zone 1–2, protecting your recovery and building sustainable endurance.
- Quality sessions push into Zone 4–5, delivering the high-intensity stimulus your body needs to adapt and improve.
- Most people without zone training accidentally spend too much time in Zone 3 — too hard to recover from, not hard enough to truly improve. This is called the "grey zone."
Personalized vs. Generic Zones
A critical limitation of generic heart rate zones is that they're calculated from a rough maximum heart rate estimate (like 220 minus your age). This is notoriously inaccurate for many people.
ZoneSteady uses the Karvonen formula, which factors in your resting heart rate alongside your age to produce personalized zone boundaries. The difference can be significant — two 35-year-olds with very different resting heart rates will have meaningfully different Zone 2 ranges.
Getting Started
1. Find your resting heart rate (check it first thing in the morning before getting up)
2. Enter your age and resting HR into ZoneSteady
3. Start a workout and watch your zone update in real time on your Apple Watch and iPhone
Training with zones doesn't require running every session at a specific pace — it just requires paying attention to how hard your heart is actually working.