What is Zone 2 Training? — Expert consensus (Seiler, Mujika et al.)
Key Findings (definition)
Zone 2 = intensity immediately BELOW the first lactate or ventilatory threshold (LT1/VT1), the intensity at which a large proportion of endurance training is proposed to be done.
Zone 2 ≠ below LT2! Many coaches incorrectly classify all sub-FTP work as "zone 2".
A 14-member panel of applied sport scientists and professional coaches agreed that zone 2 should preferably sit just under the first lactate or ventilatory threshold, done as continuous, variable or interval sessions. They expected it to bring a wide range of central and peripheral adaptations — but said these may not be specific to zone 2, since sessions slightly above or slightly below that intensity could bring them about as well.
**Practical Example:**
LT1 established by a lab or field test
Zone 2 = immediately below LT1 (true aerobic base)
Between LT1 and FTP = heavy domain (Zone 3-4), NOT zone 2
Practical Application
Expert consensus (panel of 14 sport scientists and coaches): Zone 2 is the intensity immediately below the first lactate or ventilatory threshold (LT1/VT1), delivered as continuous, variable or interval-type sessions — so anchor Zone 2 to LT1 from a lab or field test, not to a % of FTP.
The expected adaptations (broad, central and peripheral) are not unique to zone 2: the panel noted that slightly higher and slightly lower intensities can induce them too — do not treat a small drift above or below LT1 as a wasted session.
Inference, not tested: subjective markers (conversational pace, nasal breathing possible, steady HR) are a practical cross-check that a ride sits below LT1.
Inference, not tested: long rides at power just below LT2 but clearly above LT1 are heavy domain, not Z2 — avoid "grey zone" drift when the session is meant to be zone 2.
Limitations
Expert consensus is not primary experimental evidence—ranked Level B despite high agreement
Individual variation in where LT1 sits relative to LT2 is large; group rules-of-thumb miss outliers
"Zone 2" terminology varies across systems; a zone defined as a % of FTP (e.g. Coggan's "endurance" zone) is not anchored to LT1 and can overshoot it — the panel's anchor is the first lactate/ventilatory threshold
Fat-oxidation "peak" (FatMax) is not the panel's definition—"Zone 2 = fat-ox zone" is an approximation, not an identity
The abstract names no lactate or RER values for zone 2; the definition is threshold-anchored, not a fixed lactate number
How this entry was checked and changed
Why this level
(consensus-based, not primary experimental)
Content correction 2026-09-27
"steady blood lactate ≈ 1.5-2.0 mmol/L and RER 0.85-0.88" -> deleted; the abstract gives no lactate or RER values, only "immediately below the first lactate or ventilatory threshold".
"%FTP can overshoot LT1 by 10-20W", "HR steady within ±5 bpm over 60 min", "rides >3 h" -> numbers deleted; not in the abstract. Subjective-marker and grey-zone bullets relabelled as inference.
"LT1 can sit anywhere between 55-78% of VO2max power" and "Coggan Z2 defined as 56-75% FTP" -> numbers deleted; not in the abstract.
"San-Millán (mitochondrial zone)" as a source of the definition -> deleted; the abstract describes a panel of 14 experts, no named sources. Added the panel's point that the expected adaptations are not unique to zone 2.
Cross-reference labels pointed at the wrong entry or named the wrong author (checked against each cited entry's byline); repointed to the entry the label describes, or removed where the base holds no such paper.
Cross-reference descriptions checked against the cited entries' current content; wrong years, wrong entries and claims the cited entry does not make were corrected.