LT1 vs LT2: what is the difference?
LT1 is where blood lactate first lifts off baseline and marks the top of genuinely easy running. LT2 is where it accelerates away and marks the ceiling of sustainable hard running.
LT1 sits at roughly 65–75% of heart-rate reserve. It is the boundary of true aerobic easy running: below it you can talk in sentences, fuel almost entirely from a mix that leans on fat, and accumulate large volume without much recovery cost. Most of a marathon build should sit here, and the most common error in recreational training is running easy days just above it.
LT2 sits at roughly 80–88% of heart-rate reserve. Above it, lactate accumulation accelerates and the effort becomes time-limited in a way you can feel. It corresponds closely to the pace you could race for about an hour, which for most runners is somewhere between 10 km and half-marathon pace.
The gap between the two defines the three-zone model that underpins polarized and pyramidal training: Zone 1 below LT1, Zone 2 between the two thresholds, Zone 3 above LT2. Almost every discussion about training intensity distribution — 80/20, polarized, pyramidal — is a discussion about how to divide time between those three bands.
Marathon pace is the awkward one. For a well-trained runner it sits just below LT2; for a recreational runner finishing in five hours it can sit close to LT1. That is why the same session prescription genuinely means different things to different runners, and why anchoring paces to your own race times matters more than copying a plan.
Key numbers
| LT1 | 65–75% HRR | ceiling of easy running |
|---|---|---|
| LT2 | 80–88% HRR | ceiling of sustainable hard running |
| Zone 2 | between the two | the "grey zone" of the three-zone model |
Work it out for yourself
HR pacing simulator — Map your own LT1 and LT2 heart rates from your max and resting values.
Frequently asked questions
Which threshold is "threshold pace"?
LT2. When a plan prescribes a tempo or threshold session, it means the pace corresponding to the second threshold — roughly one-hour race pace, or comfortably hard.
How do I find my LT1 and LT2 without lab testing?
Heart-rate reserve percentages give a workable estimate: LT1 around 65–75% and LT2 around 80–88%. Race results give a better one — a recent 10 km or half-marathon time pins LT2 pace far more accurately than any heart-rate rule of thumb.
Sources
- Seiler (2010). What is best practice for training intensity and duration distribution in endurance athletes? International Journal of Sports Physiology and Performance.
- Stöggl & Sperlich (2015). The training intensity distribution among well-trained and elite endurance athletes. Frontiers in Physiology.
Related explainers
Glossary: LT1 (Lactate Threshold 1), LT2 (Lactate Threshold 2), HRR (Heart Rate Reserve)