Heart Rate Zones Explained — How to Train Smarter

Heart rate zone training is one of the most effective ways to structure exercise — not by how hard something feels, but by measurable physiological data. Understanding what's happening in your body at different intensities helps you train with purpose rather than just effort.

Maximum Heart Rate — The Foundation

All zone calculations start from your maximum heart rate (MHR) — the highest rate your heart can sustain. The classic formula is 220 minus your age, though more accurate formulas like Tanaka (208 − 0.7 × age) are now preferred. A 35-year-old would have an estimated MHR of about 183–184 bpm.

These are estimates. Your actual MHR can vary by 10–20 bpm from the formula and is best determined through a supervised maximal exercise test.

The Five Zones

Zone 1 — Very Light (50–60% MHR). Warm-up, cool-down, active recovery. You can hold a full conversation easily. Burns a high percentage of fat as fuel. Good for recovery days.

Zone 2 — Light (60–70% MHR). The aerobic base zone. You can speak in sentences but it's slightly effortful. This is where endurance is built — the zone elite athletes spend the majority of their training time. Primarily fat burning, develops mitochondrial density.

Zone 3 — Moderate (70–80% MHR). The "aerobic" zone. Conversation becomes difficult. Improves cardiovascular efficiency. Many recreational athletes spend too much time here — it's hard enough to feel productive, but not targeted enough to maximise either endurance or speed gains.

Zone 4 — Hard (80–90% MHR). The threshold zone. Short sentences only. This is where lactate threshold training occurs — pushing the point at which lactic acid accumulates faster than it can be cleared. Improves speed and performance at higher intensities.

Zone 5 — Maximum (90–100% MHR). All-out effort, unsustainable for more than a minute or two. Builds speed and power. Used in interval training.

The 80/20 Principle

Research on elite endurance athletes consistently shows they spend roughly 80% of training time in Zones 1–2 and 20% in Zones 4–5. Very little time in Zone 3. This "polarised" approach produces better results than the "moderate all the time" approach most recreational athletes default to. Zone 2 builds the aerobic base; Zone 4–5 sharpens performance on top of it.

Using a Heart Rate Monitor

Chest strap monitors are more accurate than wrist-based optical monitors, particularly at high intensities. Wrist monitors tend to lag and smooth the reading. For Zone 2 training — where precision matters most for staying in the right band — a chest strap is worth considering.