How do I calculate my heart-rate zones?

Most accurate: a lab test or field test (30-minute time trial). Most accessible: estimate max HR with the Tanaka formula (208 − 0.7 × age) and calculate zones as percentages. Tanaka is more accurate than the older 220 − age formula, especially for runners over 35.

What is Zone 2 heart rate?

Zone 2 is the aerobic-base zone, roughly 60–70% of max heart rate. For most runners, this corresponds to the MAF formula (180 − age). Zone 2 is the intensity at which the body builds the aerobic engine that powers ultra-distance running, and it should make up 70–85% of an ultrarunner's training volume.

How accurate is wrist-based heart rate for running?

Wrist-based optical HR is moderately accurate for steady-state easy efforts but unreliable for intervals, cold-weather running, and movements with significant arm swing. For training where HR data matters (Zone 2 base, threshold work), use a chest strap like the Polar H10 or Garmin HRM-Pro Plus. The Whoop arm strap and Polar Verity Sense armband are nearly chest-strap accurate without the discomfort.

HR Zones Explained Reference

Heart-rate zones for running. Plainly.

The five training zones — what each one is, what it feels like, and how to distribute your weekly volume across them. The reference most runners want when they buy their first chest strap.

Step one

Calculate your max heart rate.

Your zones are percentages of max HR. Use the Tanaka formula — more accurate than the older 220 − age, especially for runners over 35.

The Tanaka Formula

Max HR = 208 − (0.7 × age)

Age 30

187 bpm

Age 40

180 bpm

Age 50

173 bpm

Age 60

166 bpm

More accurate: Field-test your max HR with a 30-minute time trial, or get a lab test. Formula estimates have a ±10 bpm error band.

The five zones

The full training spectrum.

Different zones drive different physiological adaptations. Most ultrarunners spend too much time in Z3 and not enough in Z2. The fix: more easy miles, fewer "moderate" ones.

Z1 50–60% Max HR

Recovery

Walk-jog. You could hold a casual conversation in full paragraphs.

Use: Active recovery between hard sessions. Most ultrarunners under-utilize this zone.

Hours, daily

Z2 60–70% Max HR

Aerobic Base

Conversational pace. Full sentences, slightly aware of breathing.

Use: The aerobic-base zone. 70–85% of weekly running volume should be here for ultrarunners. Builds mitochondria + capillaries — the cellular machinery of endurance.

Hours — the engine of ultras

Z3 70–80% Max HR

Tempo

Comfortably hard. Three- to five-word sentences. Aware of breathing.

Use: The "gray zone" most ultrarunners get stuck in. Useful in moderation; trap if you live here. 30–60 min tempo runs once a week max.

20–60 min sessions

Z4 80–90% Max HR

Threshold

Hard. Single words. Breathing rhythmically labored.

Use: Lactate-threshold work. The pace you can hold for ~60 min all-out. 1 session per week, 3–6 × 5 min or 4 × 8 min with 2 min recoveries.

6–30 min cumulative

Z5 90–100% Max HR

VO2 Max

All-out. No talking. Cannot sustain longer than a few minutes.

Use: VO2 max work. Mile repeats, 3-min hard intervals. Once every 1–2 weeks during a base block. Rare for ultrarunners during peak training.

2–8 min cumulative

For ultrarunners specifically

Zone 2 is the engine.

70–85% of an ultrarunner's weekly volume should be in Zone 2. It's the intensity that builds aerobic capacity — the cellular machinery that lets you run for 12, 18, 30 hours without bonking.

The single most common mistake in ultra training is running easy days too hard — drifting into Z3. The fix is Zone 2 discipline: run by HR or by talk test, slow down when in doubt.

Read: The Ultimate Zone 2 Training Guide →

The 80/20 distribution

How an ultrarunner's week should look.

80% of weekly volume in Z1–Z2 (easy/aerobic). 20% in Z3–Z5 (tempo, threshold, intervals). This polarized split outperforms the gray-zone "everything moderate" approach in nearly every endurance sport study.

Mon Z2 · easy 8 mi Recovery from weekend long runs

Tue Z4 · 5 × 6 min @ threshold The one quality session of the week

Wed Z1 · easy 5 mi or rest Active recovery

Thu Z2 · easy 10 mi Mid-week medium-long

Fri Z1 · rest or 4 mi easy Pre–long-run recovery

Sat Z2 · long run 22 mi Saturday long

Sun Z2 · medium-long 14 mi Back-to-back, fatigue training

Weekly total: 63 miles. Z1 + Z2: 59 miles (94%). Z4: 4 miles (6%). Genuinely polarized.

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