Lactate Threshold
Also known as: Seuil lactique, LT1/LT2, Anaerobic threshold, OBLA
The exercise intensity above which lactate begins to accumulate in the blood faster than the body can clear it. Two thresholds are typically defined: LT1 (first inflection, ~2 mmol/L) marks the top of pure aerobic work; LT2 (second inflection, ~4 mmol/L) marks the maximal lactate steady state — the hardest pace sustainable for ~30-60 minutes.
Formula
LT1 ≈ first rise above resting lactate (~2.0 mmol/L) — the top of Zone 2.
LT2 ≈ maximal lactate steady state (~4.0 mmol/L) — the boundary between sustainable and unsustainable intensity.
Field proxy: LT2 ≈ ~85-90% of HRmax, or your 60-min time-trial pace.Example
Cyclist with FTP 250W and HRmax 190. LT1 ≈ 175W / 140 bpm (top of Zone 2, fully aerobic). LT2 ≈ 250W / 170 bpm (the FTP definition — sustainable for ~60 min). Above 250W, lactate accumulates rapidly and the clock to exhaustion starts.
How Afitpilot Uses This
We do not currently capture lactate or measured threshold values — these require lab testing or field protocols (30-min TT, ramp test) we don't yet support. Threshold-zone work is prescribed indirectly via target RPE: RPE 6-7 sits around LT1 (top of Zone 2), RPE 8-9 sits around LT2 (tempo/threshold work). The 3-zone polarized model used in our endurance prescriptions maps directly to LT1/LT2 — below LT1, between LT1-LT2 (the 'grey zone' to minimize), and above LT2 (high-intensity intervals).
Lactate threshold across athlete profiles
| Who / Context | Value | Note |
|---|---|---|
| Untrained adult | LT2 at ~50-60% of VO2max | Hits lactate accumulation very early — fatigue at low effort |
| Recreational endurance | LT2 at ~70-75% of VO2max | Years of consistent training push the threshold up |
| Elite endurance (pro cyclist, marathoner) | LT2 at ~85-90% of VO2max | Why elites can sustain near-VO2max intensities for an hour |
| Trained powerlifter | LT2 typically low (~55-65% VO2max) | Strength training does not develop the LT2 — concurrent training is required |
| Hybrid athlete (Hyrox, CrossFit) | LT2 at ~75-80% VO2max | Middle ground — enough aerobic work to push the threshold meaningfully |
| Trainability | LT2 improves 10-25% in first year of focused training | Faster gains than VO2max, which is more genetically capped |
Known Limitations
- •Threshold values drift over a season — a well-trained cyclist's LT2 can rise 20-40W over 3-6 months of focused training. A threshold measured in January is not the threshold in May.
- •Lab lactate testing and field tests (FTP, Cooper, 30-min TT) produce different numbers — typically within 5-10% of each other but not identical. Pick one method and stick with it for trend tracking.
- •Threshold is highly sensitive to glycogen status, sleep, and heat. A 'good' threshold day and a 'bad' threshold day can differ by 5-10% at the same fitness level.
- •The notion of a sharp 'threshold' is a useful simplification — in reality, lactate accumulation curves are smooth. The threshold is a model-fit inflection, not a physiological cliff.
Science Context
The dual-threshold model (LT1, LT2) traces to Kindermann (1979) and Skinner-McLellan (1980), with refinements by Mader (1976, the 4 mmol/L OBLA concept) and Coyle (1984, the lactate-steady-state framework). The threshold concept underpins virtually every modern endurance training model: Coggan's power zones, Seiler's 3-zone polarized model, and Joe Friel's heart-rate zones all reference LT1 and LT2 as anchors. Research consistently identifies LT2 (or its proxies — FTP, marathon pace, MLSS) as one of the strongest predictors of endurance performance, often better than VO2max itself.