Understanding Heart Rate Training Zones
Training in specific heart rate zones allows you to precisely target different physiological adaptations — fat burning, aerobic base building, threshold improvement, and anaerobic power. Most people make the mistake of training everything at a moderate "medium-hard" intensity, missing both the deep aerobic base work and the high-intensity stimulus needed for performance improvements.
The 5 Training Zones — What Each One Does
| Zone | % Max HR | Perceived Effort | Primary Adaptation | Fuel Source |
|---|---|---|---|---|
| Zone 1 — Recovery | 50–60% | Very easy, conversational | Active recovery, fat metabolism | Primarily fat (>90%) |
| Zone 2 — Aerobic Base | 60–70% | Easy, can hold full conversation | Mitochondrial density, fat oxidation, aerobic capacity | Fat (~85%), carbs (~15%) |
| Zone 3 — Tempo | 70–80% | Moderate — short sentences only | Aerobic efficiency, lactate clearance | Fat (~50%), carbs (~50%) |
| Zone 4 — Threshold | 80–90% | Hard — speaking is difficult | Lactate threshold, anaerobic capacity | Primarily carbs (~85%) |
| Zone 5 — VO2 Max | 90–100% | Maximum effort — very brief | VO₂max, neuromuscular power | Almost entirely carbs (>95%) |
The 80/20 Rule: How Elite Endurance Athletes Train
Research on elite endurance athletes consistently shows that roughly 80% of training volume is performed at low intensity (Zone 1–2) and only 20% at high intensity (Zone 4–5). This polarised model produces superior adaptations compared to training everything in the "moderate hard" Zone 3.
Karvonen vs. % Max HR: Which Method is More Accurate?
% Max HR (Simple)
Zones are calculated as a fixed percentage of maximum heart rate (220 − age). Fast to calculate but does not account for fitness level.
Formula: Max HR × Zone %
- ✓Simple, no equipment needed
- ✗Ignores fitness level (resting HR)
- ✗220−age formula has wide individual variation
Karvonen Formula (Recommended)
Uses Heart Rate Reserve (Max HR − Resting HR) to personalise zones based on your cardiovascular fitness level.
Formula: RHR + (HRR × Zone %)
- ✓Accounts for individual fitness level
- ✓More accurate for trained athletes
- ✗Requires accurate resting HR measurement
How to Accurately Measure Your Resting Heart Rate
Measure first thing in the morning, before getting out of bed or checking your phone.
Lie still for 2–3 minutes before taking the reading.
Use your index and middle finger on your wrist (radial pulse) or neck (carotid pulse). Count beats for 60 seconds — not 15 × 4, which is less accurate.
Average across 3–5 mornings for the most reliable result.
A wearable device (Apple Watch, Garmin, Whoop) can track this automatically during sleep — typically the most accurate reading.