What Are Heart Rate Training Zones?
Heart rate zones divide your effort levels into bands based on a percentage of your maximum heart rate (MHR). Training in specific zones produces specific physiological adaptations — time in Zone 2 builds your aerobic engine, while Zone 4–5 work improves your lactate threshold and VO₂max.
The five-zone model used here is standard across most coaching methodologies and sports science research:
| Zone | Name | % Max HR | Feel | Primary Benefit |
|---|---|---|---|---|
| Zone 1 | Recovery | 50–60% | Very easy, can sing | Active recovery, blood flow |
| Zone 2 | Aerobic Base | 60–70% | Comfortable, conversational | Fat oxidation, mitochondrial density |
| Zone 3 | Aerobic/Tempo | 70–80% | Moderate, short sentences | Aerobic capacity, tempo fitness |
| Zone 4 | Threshold | 80–90% | Hard, few words possible | Lactate threshold, race fitness |
| Zone 5 | VO₂max | 90–100% | Maximum, cannot speak | Speed, anaerobic capacity |
Why Zone 2 Training Matters Most
The majority of endurance training volume — typically 70–80% — should be done at Zone 2 intensity. This is supported by the training distribution of elite runners, cyclists, and triathletes, who overwhelmingly follow a polarised model: high volume at low intensity (Zone 1–2) and lower volume at high intensity (Zone 4–5), with relatively little time in Zone 3.
Zone 2 training specifically stimulates:
- Mitochondrial biogenesis — more mitochondria per muscle fibre
- Fat oxidation efficiency — the body gets better at using fat as fuel, sparing glycogen
- Capillary density — more blood vessels deliver oxygen to working muscles
- Cardiac stroke volume — the heart becomes more efficient per beat
These adaptations form the foundation that makes all faster training more effective. Runners who push too hard on easy days accumulate fatigue and limit their ability to perform quality hard sessions — a pattern known as the "grey zone" trap.
The Tanaka Formula vs 220 − Age
The classic 220 − age formula has been used since the 1970s, but it has significant limitations: it was never derived from a controlled study and has a standard deviation of approximately ±12 bpm. The Tanaka formula (2001) was derived from a meta-analysis of 351 studies (18,712 subjects) and is more accurate, particularly for adults over 40 where 220 − age systematically overestimates maximum heart rate.
For an average 50-year-old: 220 − 50 = 170 bpm vs Tanaka: 207 − (0.7 × 50) = 172 bpm. The difference is small at this age but grows for older individuals.
How to Find Your True Maximum Heart Rate
All formulas are estimates with ±10–15 bpm individual variation. The most accurate method is a field test:
- Warm up thoroughly — 15 minutes easy running
- Run a hard 800m (or 3-minute effort) at all-out effort on a slight uphill
- Record your peak heart rate from a chest-strap monitor during or immediately after
- Repeat 2–3 times across different sessions for reliability
The highest peak reading across multiple hard efforts is a close approximation of your true max HR. Heart rate monitors on the wrist are not accurate enough for this test — use a chest strap.
Using Heart Rate Zones for Running
For runners, heart rate training complements pace-based training. On easy and long runs, train by heart rate (Zone 2) rather than pace — this ensures you stay aerobic even when heat, fatigue, or hills push your effort level up. On tempo and interval sessions, switch to pace targets.
Use the Running Pace Calculator to find your training paces, then cross-reference with your heart rate zones to ensure your easy runs are truly easy.
Scientific References: Tanaka H, et al. (2001). Age-predicted maximal heart rate revisited. J Am Coll Cardiol. 37(1):153–156. — Seiler S & Tønnessen E. (2009). Intervals, Thresholds, and Long Slow Distance: The Role of Intensity and Duration in Endurance Training. Sportscience. 13:32–53. — Karvonen MJ, et al. (1957). The effects of training on heart rate. Ann Med Exp Biol Fenn. 35(3):307–315.