What is lactate threshold heart rate (LTHR)?
Your heart rate at the second lactate threshold, roughly what you could average racing for an hour. It usually sits at 80–88% of heart-rate reserve.
Lactate threshold heart rate, or LTHR, is your heart rate at LT2: the point where lactate starts accumulating faster than you can clear it, and the effort you could sustain for roughly an hour. Because it is tied to a physiological landmark rather than to a ceiling, it moves as your fitness changes, which makes it a better anchor for training zones than a percentage of maximum heart rate.
The standard field test is a 30-minute solo time trial on flat ground. Warm up, run the full 30 minutes as hard as you can at an even effort, and take the average heart rate of the final 20 minutes; the first ten are excluded because heart rate is still catching up with the effort. A race lasting about an hour gives a similar number — a 10 km for many recreational runners, closer to a half marathon for faster ones. Shorter races are run above threshold, so their average heart rate overstates it.
Without a test, heart-rate reserve gives a workable estimate. LT2 sits at roughly 80–88% of reserve, so LTHR ≈ resting HR + 0.80–0.88 × (max HR − resting HR). A runner with a resting heart rate of 55 and a maximum of 185 lands at 159–169 bpm, or about 86–91% of maximum. That range is the honest precision of a formula; a test or a race narrows it to a few beats.
LTHR is specific to the sport and the conditions. It is usually a few beats lower on a bike than on foot, heat and dehydration raise heart rate at any given pace, and cardiac drift pushes it upward over a long effort. A marathon is run below LTHR — typically somewhere in the high 80s to mid 90s as a percentage of it for a well-paced race, and lower for a first or slower marathon — and starting at or above it is a reliable way to blow up.
Key numbers
| LTHR | 80–88% HRR | heart rate at LT2 |
|---|---|---|
| As % of max HR | ~85–92% | varies between runners |
| Field test | 30 min solo | average HR of the last 20 min |
| Retest | every 6–8 weeks | or after a clear change in fitness |
Heart rate zones from LTHR
| Zone | % of LTHR | If LTHR is 165 bpm |
|---|---|---|
| Zone 1 — recovery | <85% | <140 |
| Zone 2 — aerobic | 85–89% | 140–148 |
| Zone 3 — tempo | 90–94% | 149–156 |
| Zone 4 — sub-threshold | 95–99% | 157–164 |
| Zone 5a — threshold | 100–102% | 165–169 |
| Zone 5b — VO₂max | 103–106% | 170–174 |
| Zone 5c — anaerobic | >106% | 175+ |
Boundaries follow Joe Friel's widely used running zones. They are conventions rather than physiological landmarks: only the line at 100% (LT2) is measured, and LT1 typically falls somewhere in the upper part of zone 1 or in zone 2. Treat the edges as soft.
Work it out for yourself
HR pacing simulator — Enter your resting and maximum heart rate to see your LT2 heart rate, and how heat and drift move you toward it over a marathon.
Frequently asked questions
How do I calculate my LTHR without a lab test?
Run a 30-minute solo time trial and average the last 20 minutes, or use a recent race of about an hour. If you only have resting and maximum heart rate, LTHR ≈ resting + 0.80–0.88 × (max − resting).
What are the LTHR zone percentages?
In Joe Friel's running scheme: zone 1 below 85%, zone 2 85–89%, zone 3 90–94%, zone 4 95–99%, and zone 5 from 100% upward, split into 5a (100–102%), 5b (103–106%) and 5c (above 106%).
Is LTHR the same as threshold pace?
They describe the same intensity in different units. Pace is more stable on a flat, cool day; heart rate is more useful on hills and in heat, when the same pace costs more. Using both and noticing when they disagree is more informative than trusting either alone.
Should I run a marathon at my LTHR?
No. LTHR is roughly one-hour race intensity. Marathon effort sits below it, and cardiac drift will raise your heart rate over the race even at a constant pace, so starting near LTHR leaves no room for the second half.
Is LTHR different from max heart rate?
Yes. Maximum heart rate is a ceiling that barely changes with training and falls slowly with age. LTHR is the heart rate at your threshold, typically 85–92% of maximum, and it is the part that responds to training.
Sources
- Friel. Quick guide to setting zones. TrainingPeaks.
- Faude, Kindermann & Meyer (2009). Lactate threshold concepts: how valid are they? Sports Medicine.
- Seiler (2010). What is best practice for training intensity and duration distribution in endurance athletes? International Journal of Sports Physiology and Performance.
- Swain & Leutholtz (1997). Heart rate reserve is equivalent to %VO₂ reserve. Medicine & Science in Sports & Exercise.
Related explainers
Glossary: LTHR (Lactate Threshold Heart Rate), LT2 (Lactate Threshold 2), HRR (Heart Rate Reserve)