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Health · 6 min read · Last updated September 2026
Age 35: Fox gives 185, Tanaka gives 183.5 — close here. At age 60 they diverge: Fox 160, Tanaka 166. Fox's equation came from a scatter of studies and systematically underestimates HRmax in older adults; Tanaka was fitted on a larger measured sample. Neither beats an actual field test (a hard, properly warmed-up effort) or a lab test.
Using Tanaka 183.5 bpm for our 35-year-old (reserve method shown because it anchors zones to resting heart rate too: HRR = HRmax − HRrest; zones = HRrest + %×HRR, with HRrest = 60): HRR = 123.5.
| Zone | % of HRmax | Feel | Example bpm (max-%) |
|---|---|---|---|
| Z1 recovery | 50–60% | Easy, conversational | 92–110 |
| Z2 aerobic | 60–70% | Comfortably breathing harder | 110–128 |
| Z3 tempo | 70–80% | "Comfortably hard" | 128–147 |
| Z4 threshold | 80–90% | Hard, short phrases only | 147–165 |
| Z5 VO₂max | 90–100% | All-out, minutes at most | 165–183 |
Most endurance training time belongs in Z1–Z2 — the "80/20" distribution popularized by polarized-training research. Zone 2 mislabeled as Z3 is the most common self-coaching error, and it usually comes from an HRmax formula that underestimates your true max.
Tanaka (208 − 0.7×age) tracks measured maxima better than the classic 220 − age, especially over 40. Both carry roughly ±10–12 bpm error — treat the output as a starting band, then adjust with a field test or how effort actually feels.
Zone 2 is the intensity where you can hold a conversation with slightly longer breaths — roughly 60–70% of max heart rate. It builds aerobic base with low stress and is where most weekly endurance volume is best spent.
They lower both resting and maximum heart rate substantially, so percentage-of-max formulas computed from age alone will mislead. Anyone on such medication should set zones with their doctor or use perceived-exertion scales instead.
For adults, 60–100 bpm is the usual reference band, with well-trained people often in the 40s–50s. A sudden sustained rise from your own normal can signal illness, overtraining or dehydration — it is a trend worth watching, not a single reading.