Heart Rate Zones Explained
A complete reference for the five heart rate training zones — Zone 1 recovery (50–60%), Zone 2 endurance (60–70%), Zone 3 aerobic (70–80%), Zone 4 threshold (80–90%), Zone 5 maximum (90–100%).
What Actually Happens Inside Each Zone
Percent-of-HRmax is a proxy. The real story is metabolic — which fuels dominate, whether lactate accumulates, and which cellular adaptations are being trained.
| Zone |
Primary fuel |
Blood lactate |
Cellular adaptation |
Sustainable time |
| Z1 · Recovery | Fat | < 1.5 mmol/L | Parasympathetic recovery, capillarisation | Hours |
| Z2 · Endurance | Fat (dominant) + carbs | 1.5–2 mmol/L | Type I fibre mitochondrial density | 2–5 hours |
| Z3 · Aerobic | Carbs (dominant) | 2–4 mmol/L | Aerobic enzyme activity | 45–90 min |
| Z4 · Threshold | Carbs (near-exclusive) | ~4 mmol/L (LT2) | Lactate clearance, buffering | 20–60 min |
| Z5 · Maximum | Carbs + anaerobic | 6–12 mmol/L | VO₂max, stroke volume, Type II recruitment | 1–8 min |
The Two Thresholds That Define the Zones
Sport scientists divide intensity by two physiological breakpoints, not by arbitrary percentages:
- LT1 (first lactate threshold) — the intensity above which blood lactate first rises measurably above baseline (~2 mmol/L). Marks the top of Zone 2.
- LT2 (second lactate threshold, MLSS) — the highest intensity at which lactate production and clearance remain balanced (~4 mmol/L for most). Marks the top of Zone 4.
Percent-of-HRmax zones (50–60, 60–70, etc.) are a convenient shortcut that maps roughly onto these thresholds for the average adult. Your personal thresholds may sit 5–10 percentage points above or below the textbook numbers, especially if you are highly trained or very deconditioned.
Heart Rate Zones (reference: age 30, HRmax ≈ 187 bpm, Tanaka)
| Zone |
Name |
% HRmax |
BPM (age 30) |
Primary use |
| 1 | Recovery | 50–60% | 94–112 | Warm-up, recovery, active rest |
| 2 | Endurance | 60–70% | 112–131 | Aerobic base, fat oxidation |
| 3 | Aerobic | 70–80% | 131–150 | Tempo, aerobic capacity |
| 4 | Threshold | 80–90% | 150–168 | Lactate threshold intervals |
| 5 | Maximum | 90–100% | 168–187 | VO₂ max, neuromuscular power |
What Each Zone Feels Like (Talk Test)
- Zone 1 · Recovery: You can sing.
- Zone 2 · Endurance: You can hold a full conversation.
- Zone 3 · Aerobic: Speaking becomes noticeably harder.
- Zone 4 · Threshold: Only short phrases of a few words.
- Zone 5 · Maximum: Almost impossible to speak.
Frequently Asked Questions
How accurate are heart rate calculators?
Formula-based calculators typically estimate HRmax within ±10–15 bpm. They are accurate enough to structure training for recreational athletes but not a substitute for a supervised max test.
What is the Karvonen method?
Karvonen uses heart rate reserve (HRR = HRmax − HRrest). Target HR = HRrest + (Intensity% × HRR). It personalises zones by accounting for resting heart rate.
Should I use different zones for cycling vs running?
Your bpm targets stay the same, but heart rate response differs by sport. Cycling HR is typically 5–10 bpm lower than running at equivalent perceived effort due to the seated position.
Is Zone 2 the best zone for fat loss?
Zone 2 maximises the percentage of calories from fat, but higher intensities burn more total calories per minute. Long-term fat loss is driven by total weekly energy balance.
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