Most amateur runners train in a no-man’s-land: too hard to build aerobic base, too easy to sharpen speed. Heart rate zones exist to stop exactly that — and the surprise is how slow effective training mostly is.
The Five Zones
Anchored to your max HR (rough formula: 208 − 0.7 × age): Z1 50–60% recovery · Z2 60–70% aerobic base · Z3 70–80% tempo · Z4 80–90% threshold · Z5 90%+ maximal. A 40-year-old’s max ≈ 180, putting Zone 2 at roughly 108–126 bpm — conversational pace, embarrassingly gentle.
Why Zone 2 Builds Champions
Z2 work grows mitochondria, capillaries and fat-burning capacity — the machinery every faster pace runs on — while being recoverable enough to repeat daily. Elite endurance athletes famously follow ~80/20: four-fifths of training genuinely easy, one-fifth genuinely hard. Amateurs invert it, live in Zone 3, and plateau.
Using the Zones
- Easy days: hold Z2 even when it means walking hills — ego is the enemy
- One or two quality sessions weekly in Z4–Z5 (intervals, threshold)
- Resting heart rate creeping up over several days = accumulated fatigue or oncoming illness; the morning number is a free coach
Calibrate Properly
Formulas mis-estimate individuals by ±10 bpm. If a chest strap and a hill sprint test are available, measure your real max — every zone inherits the accuracy.