Lactate Threshold Training: LT1 & LT2 Explained

What is the lactate threshold?

Lactate is a by-product — and fuel — of carbohydrate metabolism that circulates in your blood at all times. At easy intensities, production and clearance stay in balance, so concentration hovers around a baseline of roughly 1–2 mmol/L. As intensity rises, production eventually outpaces clearance and blood lactate climbs. The intensities where this balance visibly changes are your lactate thresholds — the most direct physiological anchors for training zones that exist.

What is the difference between LT1 and LT2?

LT1, often called the aerobic threshold, is the first intensity at which lactate rises meaningfully above baseline. Below it, you can ride for hours; it marks the ceiling of true endurance riding. LT2 — the anaerobic threshold, closely related to MLSS (maximal lactate steady state) — is the highest intensity at which lactate remains stable. Above LT2, lactate accumulates rapidly and the clock starts ticking. Classic field markers put LT1 near 2 mmol/L and LT2 near 4 mmol/L, though individual curves vary — which is exactly why measuring your own values beats generic formulas.

Why train with LT1 and LT2 instead of FTP alone?

FTP is a single power number estimated from performance. LT1 and LT2 are two measured physiological markers, and the gap between them tells you more than either alone. Polarized and pyramidal training models — the backbone of most endurance programs — are defined in terms of these thresholds: the bulk of volume below LT1, targeted quality work around and above LT2. Two riders with identical FTP can have very different thresholds, and therefore need different zone boundaries.

How do you test your lactate thresholds at home?

You need a handheld lactate meter (such as Lactate Plus or Lactate Pro 2), test strips, and a controlled protocol on a smart trainer. The standard approach is a graded step test:

• Warm up 10–15 minutes at an easy pace.
• Ride steps of 3–5 minutes, starting well below your expected LT1 and increasing power by 20–25 W per step (ERG mode makes the steps precise).
• Take a small blood sample from your earlobe or fingertip at the end of every step and note the value with the step's power.
• Stop when lactate clearly exceeds ~4–6 mmol/L or you can no longer hold the step.
• Plot lactate against power: the first sustained rise above baseline is LT1, the point where the curve steepens sharply is LT2.

How do you train with LT1 and LT2 zones?

Once you know both thresholds, the structure is straightforward. Ride the majority of your volume — typically around 80% — below LT1, where aerobic adaptations accumulate with minimal fatigue cost. Place your quality work deliberately: sweet-spot and threshold sessions just below LT2 raise sustainable power, while intervals above LT2 develop VO2max and race-winning capacity. Re-test every 6–8 weeks: as fitness improves, both thresholds shift right and your zones should follow.

How does ENDURE estimate LT1 and LT2?

ENDURE is the first cycling app that lets you log lactate readings directly during a ride — or add them afterwards from your activity history. The app fits a curve through your readings and automatically estimates LT1 and LT2, including a confidence tunnel that shows how solid the estimate is. Your blood markers live next to your power data instead of in a spreadsheet, and every new reading refines the picture. Available in Early Release on iOS and Android.