Lactate threshold heart rate: how to find it and use it

Lactate threshold heart rate is the most useful heart rate number you probably don't know. Not your max, which you've likely never hit. Not your resting heart rate, which mostly tells you how you slept. The heart rate you can sit at for a long, hard effort before things start falling apart.

Know it, and your tempo and threshold runs stop being guesswork. Ignore it, and your "hard" runs drift between too easy and accidentally racing. This post covers what lactate threshold heart rate is, how heart rate and lactate threshold relate, how to determine lactate threshold heart rate without a lab, and how to use it, whether you schedule your week by hand or with a running app that adapts to your lifting.

What is lactate threshold heart rate?

As you speed up, your body passes two turning points. The first is where blood lactate starts rising above resting levels. The second is the highest intensity where lactate production and clearance still balance, the maximal lactate steady state (Faude, Kindermann and Meyer, 2009). When runners and coaches say "lactate threshold", they almost always mean the second one.

Your lactate threshold heart rate (LTHR) is simply the heart rate that goes with that second turning point. It's the heart rate of an effort that's comfortably hard: a few words at a time, sustainable for a while, then very suddenly not.

In the five-zone, percent-of-max model we use across this blog, threshold lives in zone 4, 80–90% of max heart rate, roughly RPE 7–8. If you want to see where that band falls for you, plug your max heart rate into your personal zones.

For the physiology in more depth and the full set of testing options, here's how to test lactate threshold. This post is about the heart rate number itself.

Heart rate and lactate threshold: how they relate

Heart rate doesn't measure lactate. It rises with effort, and lactate threshold happens at a certain effort, so the two line up well enough to be useful. But three caveats matter.

Where threshold falls as a percentage of max varies by person. In one well-known trial, researchers used 85% of max heart rate as their "lactate threshold" intensity (Helgerud et al., 2007), which sits in the middle of our zone 4. That's a reasonable group average, not your number. A 2020 review concluded that fixed percentages of maximal anchors like max heart rate have little merit for putting different people in the same physiological state (Jamnick et al., 2020).

Heart rate drifts at threshold. When trained cyclists rode at their maximal lactate steady state until they couldn't continue, they lasted 55 minutes on average, and heart rate rose significantly throughout (Baron et al., 2008). So your heart rate in minute 25 of a threshold effort is higher than in minute 5, at the same pace.

Heart rate lags. It takes a few minutes to catch up at the start of a hard effort. Don't chase the number early in a rep.

That's why a tested lactate threshold heart rate beats any formula, and why you should still use feel alongside it.

How to determine lactate threshold heart rate

Three routes, from most accurate to most practical.

1. A lab test

A graded treadmill test with small blood samples at each stage gives you a lactate curve, and from it a threshold heart rate and pace. It's accurate, but which threshold you get depends on the method the lab uses. Faude and colleagues found 25 different lactate threshold concepts in the research literature (Faude, Kindermann and Meyer, 2009). Ask which one they report.

2. The 30-minute field test

Coach Joe Friel's field test is the most widely used DIY method:

1. ›Warm up well: 15 minutes easy plus a few strides.
2. ›Run 30 minutes solo, as hard as you can sustain for the full 30, like a race.
3. ›Press lap at 10 minutes.
4. ›Your average heart rate for the last 20 minutes is your estimated lactate threshold heart rate.

Why the last 20? The first ten minutes include the lag while heart rate climbs. Average pace over the same 20 minutes gives you a working threshold pace too.

Test conditions matter more than people think:

• ›Flat route or track, mild weather, no group to race.
• ›Not the day after heavy squats or a long run.
• ›Same route and similar conditions each time, so retests compare like with like.
• ›If you track heart rate menstrual cycle patterns, test at a similar point in your cycle each time for the same reason.

It's a genuinely hard session. Treat it as one of your hard days for the week.

3. Estimate from effort

No test, no lab: run at an effort you'd rate 7–8 out of 10, where you can manage only a few words at a time, and note the heart rate once it settles. A 2022 review found that RPE and the talk test are valid markers of the respiratory compensation threshold, which sits close to lactate threshold (Bok, Rakovac and Foster, 2022). It's rougher than a test, but it's free and it's better than a birthday.

Is there a lactate threshold calculator for heart rate?

Not one that knows your number. Any lactate threshold calculator based on heart rate alone is doing arithmetic on an estimate of an estimate: an age formula for max, then a percentage of it.

If you want a starting band anyway, here's that arithmetic in the open. Our zone 4 is 80–90% of max:

Your lactate threshold heart rate is somewhere around there, if your max is right. Run the field test and you'll know.

A useful cross-check: once you have a tested LTHR, it should land inside your zone 4. If it lands in zone 5, your max heart rate estimate is probably too low. If it lands in zone 3, your estimate is probably too high, or the test wasn't run all-out.

How to use your lactate threshold heart rate

Threshold runs

Threshold sessions sit right around your LTHR: cruise intervals like 4 × 8 minutes with short jogs, or 20–30 minutes continuous for experienced runners. Expect heart rate to reach your LTHR a few minutes into each rep and creep slightly above it late in long efforts. Our guide to threshold runs covers the sessions and pacing in detail.

Tempo runs

Tempo runs usually sit at or a few beats under your LTHR, for 20–40 minutes. Slightly easier than threshold, slightly longer.

Easy runs

Your LTHR also tells you where not to be on easy days. If an "easy" run is creeping toward your threshold heart rate, it isn't easy.

Races

For a 10K, many runners spend much of the race around or above LTHR. For a half marathon, many sit near or a little under it. Marathon heart rate explained simply: for most runners it sits well below threshold early on and drifts up as the race goes on. Use LTHR as a ceiling to respect in the first half of longer races, not a target.

Lactate threshold heart rate vs VO2 max

They measure different things. VO2 max is your aerobic ceiling. Lactate threshold is how close to that ceiling you can work for a long time.

• ›If you want to know what a good VO2 max is, and how to raise it, the answer is mostly easy running plus a small dose of very hard intervals.
• ›If you want to see how your number compares, a VO2 max chart by age and sex gives lab-tested percentiles.

Threshold training raises how much of your engine you can use; VO2 max work raises the engine. Both move race times.

How often to retest

Every 6–12 weeks, or whenever threshold sessions start feeling suspiciously easy at the same heart rate. As fitness improves, your threshold pace should get faster. Track pace and heart rate together so you can see which one moved.

Common mistakes

• ›Using an age formula as your LTHR. It's a starting point, not a test result.
• ›Testing in a group. Racing someone turns a test into a race. Run it solo.
• ›Testing tired. Heavy legs from yesterday's squats will give you a low number.
• ›Chasing LTHR in the first minutes of a rep. Heart rate lags. Run the effort and let the number catch up.
• ›Mixing systems. Friel's threshold-based zones are numbered differently from the percent-of-max model on this blog. Pick one system per plan.

How exrsz handles threshold training

exrsz builds a periodized plan from your goal, schedule, level and equipment, with threshold and tempo sessions placed as planned hard days and easy running around them. It balances those sessions against your lifting in one plan, adapts each week to how you actually trained, and reshuffles missed sessions rather than cramming them in.

FAQ

What is lactate threshold heart rate?

It's the heart rate that corresponds to your lactate threshold, the highest intensity at which lactate production and clearance still balance. In a percent-of-max model it usually sits in zone 4, at 80–90% of max heart rate.

How do I determine my lactate threshold heart rate?

Run a solo 30-minute all-out effort, press lap at 10 minutes, and take your average heart rate for the last 20 minutes. A lab test with blood lactate is more precise, but the field test is good enough for most runners.

What percentage of max heart rate is lactate threshold?

It varies by person. One trial used 85% of max heart rate as its lactate threshold intensity (Helgerud et al., 2007), but fixed percentages of max don't put everyone at the same physiological intensity (Jamnick et al., 2020).

Is there a lactate threshold calculator based on heart rate?

Only a rough one: estimate your max heart rate and take 80–90% for a zone 4 band. A field test gives a far better number than any calculator.

Does lactate threshold heart rate change with training?

It can, and your threshold pace should improve as you get fitter. Retest every 6–12 weeks so your training targets keep up with your fitness.