Lactate threshold: what it is, how to test it, and how to raise it

Lactate threshold is the most useful number in endurance training that almost nobody knows. Not your VO2 max, not your max heart rate, not your 5K PR. The pace and heart rate you can hold for a long time before everything starts falling apart quickly.

Raise it and you can hold faster paces for longer, which is most of what distance racing is. Ignore it and you'll keep doing random hard runs that feel productive and change very little. Here's what lactate threshold is, how to run a lactate threshold test without a lab, and how to train it, whether you plan your week by hand or use an app that schedules runs around your gym days.

What is lactate threshold?

When you exercise, your muscles produce lactate, and your body clears it. At easy intensities, clearance keeps up and blood lactate stays near resting levels. As you speed up, you pass two turning points:

1. ›The first threshold (LT1): the intensity where blood lactate starts to rise above baseline.
2. ›The second threshold (LT2): the highest intensity where lactate production and clearance are still in balance, known in the lab as the maximal lactate steady state (MLSS). Above it, lactate keeps climbing and the clock on your effort starts ticking.

That two-breakpoint framework is how Faude, Kindermann and Meyer (2009) describe the "aerobic-anaerobic transition" in their review of threshold concepts. They found 25 different ways researchers define a lactate threshold, which explains why the term is confusing. When coaches and runners say "lactate threshold" or just "threshold", they almost always mean the second one. That's how we use it here.

Why it matters: the same review reports that most studies comparing lactate thresholds with endurance performance found strong correlations, particularly for running events. Your threshold is a good predictor of how fast you can race.

Where it sits in training by heart rate: threshold lives in zone 4, 80–90% of max heart rate, roughly RPE 7–8. The first threshold sits around the top of zone 2. Easy running stays below LT1; threshold running sits right around LT2. Zone 3 is the territory between them. If you'd like to see where those bands fall for your age and max heart rate, this zone 2 calculator lays out all five zones.

What threshold effort feels like

Threshold is "comfortably hard". Not a sprint, not a jog.

• ›You can say a few words, not sentences.
• ›Breathing is deep and rhythmic, but controlled.
• ›It feels sustainable for a while, then very suddenly isn't.
• ›Many coaches describe it as roughly the effort you could race for about an hour if you had to. Fitter runners can hold it longer; newer runners less.

Speed play is a gentle introduction to this feeling. A few fartlek runs, with short surges up to threshold effort and easy running between them, teach you where the line is without a stopwatch.

How to test your lactate threshold

There are three routes, from most accurate to most practical.

1. A lab lactate threshold test

A graded test on a treadmill or bike: the speed or power goes up in stages, and a technician takes small blood samples (usually from a fingertip or earlobe) to measure lactate at each stage. You get 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, since there are so many definitions (Faude et al., 2009). Ask which one they report.

2. The 30-minute field test

Coach Joe Friel's field test for lactate threshold heart rate is the most widely used DIY version:

1. ›Warm up well.
2. ›Run 30 minutes solo, as hard as you can sustain for the whole 30 minutes, as if it were 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.

Many runners also use their average pace over the same stretch as a working threshold pace. Run it on a flat route or a track, in mild weather, and not the day after heavy squats. It's a genuinely hard session, so treat it like one. Heads up: Friel's own zones are built on percentages of this threshold heart rate and numbered differently from the five-zone, percent-of-max model we use, so don't mix the two systems in one plan.

3. Estimate from effort

No test, no lab: run at an effort you'd rate about 7–8 out of 10, where you can manage only a few words at a time. Subjective markers aren't as crude as they sound. A 2022 review found that RPE and the talk test are valid markers of the second ventilatory threshold, which sits close to lactate threshold (Bok, Rakovac and Foster, 2022). Giving yourself an RPE target of 7–8 for threshold work is a perfectly good place to start.

Whichever method you use, retest every 6–12 weeks, or whenever threshold sessions start feeling suspiciously easy.

How to raise your lactate threshold

Threshold improves from two directions: lots of easy running underneath it, and some focused work at or near it.

Build the base underneath it

The bigger your aerobic base, the higher your threshold can sit. Well-trained endurance athletes do most of their sessions at low intensity, with a smaller share of hard work (Seiler, 2010). That easy volume is how zone 2 builds your engine, and for runners specifically, what is zone 2 running covers how slow those runs should actually be.

Do threshold sessions

The classic threshold workouts, as practiced by most coaches:

Threshold runs and tempo runs overlap a lot: threshold usually means right at LT2, tempo is often used for a slightly easier, longer effort just under it. Breaking threshold work into intervals lets you accumulate more time at the right intensity with less fatigue than one long block.

One session a week is a good start for most recreational runners. Two is plenty for nearly everyone.

Don't make every hard session a threshold session

Threshold training is effective, but it isn't the only tool. In Helgerud et al. (2007), four groups did the same total work for eight weeks; the groups doing 4 × 4-minute intervals at 90–95% of max heart rate improved VO2 max more than the group training at lactate threshold (85% of max). And in a nine-week study in well-trained athletes, a polarized mix of mostly easy work plus high-intensity intervals beat a threshold-focused program on most endurance markers (Stöggl and Sperlich, 2014).

The takeaway isn't "skip threshold". It's balance. Threshold raises how much of your engine you can use; VO2 max work raises the size of the engine. Knowing how to improve VO2 max matters once threshold sessions alone stop moving the needle, and the choice of tempo run vs interval run depends on which of those two is holding you back.

Threshold training for hybrid athletes

If you lift too, threshold sessions count as hard days. A 30-minute tempo at RPE 7–8 sits alongside heavy squats in your weekly fatigue budget, not underneath it.

• ›Keep threshold runs away from the day before or after your heaviest lower-body session.
• ›Pair them with upper-body lifting if you must double up.
• ›In a strength-priority block, one threshold session a week is enough to hold fitness.

Before a race, threshold work gets shorter rather than disappearing. That's the logic of tapering: cut volume, keep a little intensity so you stay sharp.

Lactate threshold, VO2 max and other numbers

Threshold isn't the only fitness marker you'll hear about.

• ›VO2 max is your aerobic ceiling; threshold is how close to it you can work for a long time. If you want to see how your estimate compares with others, a VO2 max chart by age and sex gives the reference ranges.
• ›Lactate threshold heart rate is the heart rate that goes with your threshold, and it's what most threshold-based zone systems are built on.
• ›VO2 max workouts are short, very hard intervals, mostly in zone 5.
• ›The Cooper test, a 12-minute run for distance, is an old field estimate of aerobic capacity (Cooper, 1968).

How exrsz handles threshold training

exrsz builds a periodized plan from your goal, schedule, level and equipment. Threshold and tempo sessions show up as planned hard days, with easy running around them and your heavy lifting kept out of their way. Each week adapts to how you actually trained, and missed sessions get reshuffled rather than crammed in.

FAQ

What is lactate threshold?

Lactate threshold is the highest intensity at which your body can still clear lactate as fast as it's produced. Above it, lactate builds up quickly and the effort becomes unsustainable for long.

How do I test my lactate threshold without a lab?

Run a solo 30-minute all-out effort, press lap at 10 minutes, and take your average heart rate for the last 20 minutes as your estimated lactate threshold heart rate. Many runners use their average pace for that stretch as a working threshold pace.

What heart rate zone is lactate threshold?

In the five-zone model based on max heart rate, threshold sits in zone 4, at about 80–90% of max heart rate, or RPE 7–8.

How often should I do threshold runs?

Once a week works for most recreational runners; twice is plenty even for experienced ones. Keep the rest of your running mostly easy.

Can you improve your lactate threshold?

Yes. A consistent base of easy running plus regular threshold sessions such as tempo runs and cruise intervals are the standard ways to raise it.