Heart rate zones explained
Heart rate zones divide effort into bands, from very easy to all-out. Understanding them helps you train with purpose — and explains why Zone 2 means different things in different places.
The five-zone system
| Zone | % of max HR | Feels like | Typical purpose |
|---|---|---|---|
| 1 | 50–60% | Very easy; easy conversation | Recovery, warm-up, general activity |
| 2 | 60–70% | Easy; full sentences | Aerobic base, endurance, fat use |
| 3 | 70–80% | Moderate; shorter sentences | Aerobic capacity, "tempo" |
| 4 | 80–90% | Hard; a few words | Threshold, race pace |
| 5 | 90–100% | Maximal; no talking | Short intervals, top-end speed |
Percentages vary slightly between devices and coaches. With the Karvonen method the same percentages are applied to heart rate reserve instead of maximum.
How official guidelines line up
Public health bodies use broader categories. The American Heart Association describes moderate intensity as about 50–70% of maximum heart rate and vigorous as about 70–85%. The American College of Sports Medicine's classification puts moderate intensity at 40–59% of heart rate reserve (55–69% of maximum) and "hard" at 60–84% of reserve. Zones 1–2 broadly correspond to moderate activity; Zones 3–4 to vigorous.
The three-zone research model
Exercise scientists often use three zones anchored to physiological thresholds: Zone 1 below the first lactate or ventilatory threshold (blood lactate below about 2 mmol/L), Zone 2 around the lactate threshold (about 4 mmol/L), and Zone 3 above it. In that model, the "Zone 2" popularised in fitness media is actually Zone 1. When reading research, always check which model is used.
Which zones should you train in?
Most training for health and endurance should be easy (Zones 1–2), with a smaller amount of harder work. Elite endurance athletes typically spend around 80% of training at low intensity. See how much Zone 2 per week and get your own zone table from the calculator.
Frequently asked questions
Why does my watch show different zones from this calculator?
Devices use different formulas and zone boundaries. Some use percentage of maximum, others heart rate reserve or lactate threshold estimates. You can usually set custom zones in the app to match your calculator results.
Which zone is best for heart health?
Public health guidelines focus on moderate and vigorous activity overall. A mix — mostly Zones 1–2, with some Zones 3–4 if you are able — covers both. Check with your doctor if you have a heart condition.
Is Zone 3 bad?
No, but spending most sessions there — the "moderately hard" middle — tends to cause fatigue without the full benefits of truly easy or truly hard training.
Medical note: This is general information, not medical advice. Heart rate formulas are estimates. If you have a heart condition, high blood pressure, diabetes, take medication that affects heart rate (such as beta-blockers), are pregnant, or are new to exercise, ask a doctor before changing your training. Stop and seek help if you feel chest pain, severe breathlessness, dizziness or palpitations. Full disclaimer.
Calculate your Zone 2 heart rate
Sources
- American Heart Association, "Target Heart Rates Chart" (last reviewed Aug 2024)
- Pollock ML et al. "ACSM Position Stand: The recommended quantity and quality of exercise…" Medicine & Science in Sports & Exercise 1998;30(6):975–991
- Stöggl TL, Sperlich B. "The training intensity distribution among well-trained and elite endurance athletes." Frontiers in Physiology 2015;6:295