How Zone 2 Heart Rate Calculator works
Methodology for the Zone 2 Heart Rate Calculator: formulas, coefficients, data sources, assumptions, and known limitations.
Scope
Estimates the Zone 2 aerobic training range using four independent definitions: Maffetone 180-age, Karvonen at 60–70% HRR, a straight 60–70% of max HR, and a lactate-threshold-anchored range.
Zone 2 is the intensity where mitochondrial adaptation and fat oxidation dominate. The definitions differ enough that the right choice depends on your training history.
Formula
Maffetone: ceiling = 180 - age (+/- adjustments). Karvonen Z2: (MHR - RHR) * [0.60, 0.70] + RHR. %MHR Z2: MHR * [0.60, 0.70]. LT-anchored Z2: [0.80, 0.88] * LTHR.
Coefficients
| Parameter | Value | Note |
|---|---|---|
| Maffetone adjustments | -10 (major illness/return), -5 (new to training), +5 (competitive, 2+ yrs consistent) | |
| Karvonen Z2 intensity | 0.60 – 0.70 HRR | |
| LTHR-anchored Z2 | 0.80 – 0.88 of LTHR |
Data sources
- Maffetone P. The Maffetone Method. Ragged Mountain Press, 1999. — Author reference page documenting the 180-age formula and its adjustment rules.
- Karvonen MJ, Kentala E, Mustala O. The effects of training on heart rate; a longitudinal study. Ann Med Exp Biol Fenn. 1957;35(3):307-315. — PMID 13470504. Origin of the heart-rate reserve formula.
- Seiler S. What is best practice for training intensity and duration distribution in endurance athletes? Int J Sports Physiol Perform. 2010;5(3):276-291. — PMID 20861519. Background on the polarized/pyramidal model and the role of Z2.
- San-Millán I, Brooks GA. Assessment of metabolic flexibility by means of measuring blood lactate, fat, and carbohydrate oxidation responses to exercise in professional endurance athletes and less-fit individuals. Sports Med. 2018;48(2):467-479. — PMID 28623613. Metabolic rationale for training at the Zone 2/LT1 intensity.
Assumptions
- If a lactate threshold HR (LTHR) is known from a 30-minute time-trial field test, use the LT-anchored range — it is the most individually calibrated.
- Resting HR is a true resting reading, not a post-coffee reading.
Approximation range
Maffetone tends to prescribe the most conservative ceiling, especially for lifters and short-course athletes moving into endurance.
Karvonen-HRR tends to fall 5–10 bpm above the Maffetone ceiling for the same athlete.
All four definitions agree within ~12 bpm for typical adults; the spread is the point of displaying them together.
Limitations
- No HR-based zone definition can distinguish between fat-oxidation-dominant and carbohydrate-dominant work at the same HR; metabolic cart or lactate testing is the ground truth.
- HR drift on long runs inflates numbers by 5–15 bpm vs minute-1 of the same effort; Z2 prescriptions should be taken as 'HR at minute-20 steady state'.
- Stimulants, dehydration, and heat materially shift zones.
Reproducibility
35 yo, MHR 185, RHR 55, LTHR 162. Maffetone ceiling 180-35 = 145. Karvonen Z2 (0.60–0.70): (185-55)*0.60+55 = 133; (185-55)*0.70+55 = 146. %MHR Z2: 111–130. LT-anchored Z2: 0.80*162 = 130; 0.88*162 = 143.
Change log
- 2026-04-24: methodology page first published.
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