Most people approach cardio one of two ways: they go all-out until they can't breathe, or they plod along at a comfortable pace. Both can produce results, but neither is particularly strategic. Heart rate zone training gives you a framework to get specific outcomes from specific workouts — and it starts with understanding five distinct effort levels.
What Are Heart Rate Zones?
Heart rate zones divide your maximum heart rate (MHR) into ranges, each corresponding to a different physiological state and training benefit. Most systems use 5 zones, though some use 3 or 7.
The foundation of all zone calculations is your Maximum Heart Rate (MHR), estimated with the formula: MHR = 220 − your age. A 35-year-old would have an estimated MHR of 185 bpm.
The 5 Heart Rate Zones
Zone 1: Active Recovery (50–60% MHR)
This is a very light effort — a gentle walk or easy cycling. You can hold a full conversation. Zone 1 promotes blood flow, reduces muscle soreness, and aids recovery without adding stress. Use it on rest days or as warm-up/cool-down.
Zone 2: Aerobic Base (60–70% MHR)
Often called "fat-burning zone," this is a comfortable, sustainable pace where you can speak in full sentences but are clearly breathing harder. Zone 2 is the most important zone for building endurance, improving mitochondrial efficiency, and enhancing fat metabolism. Elite endurance athletes spend 70–80% of their training here.
Zone 2 feels almost too easy — that's the point. The adaptation happens at the cellular level over weeks and months. If you're breathing hard, you've gone too fast.
Zone 3: Tempo (70–80% MHR)
Moderate-to-hard effort where conversation becomes difficult — a few words at a time. Zone 3 improves aerobic capacity and lactate threshold. Many recreational runners spend too much time here — hard enough to cause fatigue, but not hard enough to drive the adaptations of Zone 4 or 5.
Zone 4: Threshold (80–90% MHR)
Hard effort where you can barely speak. This is near your lactate threshold — the point at which lactate accumulates faster than your body can clear it. Zone 4 intervals dramatically improve your ability to sustain higher speeds, making it essential for race preparation and performance training.
Zone 5: Maximum Effort (90–100% MHR)
All-out effort that can only be sustained for short bursts — seconds to 2 minutes maximum. Zone 5 develops peak power, VO2 max, and neuromuscular coordination. Think sprint intervals, hill repeats, or high-intensity interval training (HIIT).
How to Structure Your Training Across Zones
Research supports the 80/20 principle: elite endurance athletes spend roughly 80% of their training in Zones 1–2 and 20% in Zones 4–5. Zone 3 — the "grey zone" — is largely avoided because it's too hard for recovery and not hard enough for maximum adaptation.
For recreational fitness, a good weekly structure might be:
- 2–3 Zone 2 sessions (30–60 min each)
- 1 Zone 4 interval session (e.g., 4×8 min at threshold)
- 1 Zone 5 HIIT session (e.g., 8×30 sec sprints)
Calculate Your Heart Rate Zones
Enter your age and resting heart rate to get your personalised training zones instantly.
Open Heart Rate Calculator →Using a Heart Rate Monitor
Chest strap monitors are the most accurate option. Wrist-based monitors (smartwatches) are convenient but can be off by 10–15 bpm during high-intensity work due to movement artefacts. For casual training, either works. For precise zone training, a chest strap is worth the investment.
The Bottom Line
Heart rate zone training replaces "train by feel" with precision. By spending the right amount of time at the right intensity, you build specific fitness qualities, reduce injury risk, and make every workout purposeful. Start by calculating your zones, and try one Zone 2 session this week — you'll likely be surprised how slow "slow" needs to be.