Lactate threshold, explained: the two lines every runner crosses

What is lactate threshold in running?

Lactate threshold is the boundary between intensities your body can sustain in a steady state and those it cannot. There are two such boundaries: LT1, where blood lactate first rises above its resting baseline, and LT2, the highest intensity at which lactate production and clearance stay in balance.

The vocabulary is a mess. A 2009 review by Faude, Kindermann and Meyer found 25 lactate threshold concepts in three families: fixed lactate values, the first rise above baseline, and the maximal lactate steady state or a distinct change in the lactate curve. Beneath the names, the same two breakpoints recur.

Other names map onto the same two lines. Aerobic threshold, VT1 (the first ventilatory threshold, where breathing first quickens out of proportion to effort) and the gas exchange threshold sit at or near LT1. Anaerobic threshold, VT2, onset of blood lactate accumulation, maximal lactate steady state and critical speed aim at the upper line, each landing slightly differently.

Is lactate a waste product?

No. That idea is decades out of date. In his 2018 review of lactate shuttle theory, George Brooks describes lactate as a major energy source, the major precursor for making new glucose, and a signaling molecule. Muscles, the heart and the brain take it up and burn it.

Rising blood lactate is a marker, not a toxin: lactate is being produced faster than it is cleared, as you lean harder on carbohydrate under greater metabolic stress. The burn of hard running is real; blood lactate is simply a convenient window onto the intensity behind it.

Is lactate threshold the same as anaerobic threshold?

Roughly, both names point at the same upper line, but nothing switches from aerobic to anaerobic there. Muscles keep using oxygen above it and produce some lactate well below it. A 2021 review in the Journal of Physiology by Poole, Rossiter, Brooks and Gladden calls the term a misnomer and describes 50 years of controversy over it.

They place the meaningful upper boundary at critical power, or critical speed for runners, the line between heavy and severe intensity: below it, oxygen uptake and lactate settle; above it, they climb until you stop. The maximal lactate steady state is only notionally similar to critical power and can sit somewhat below it.

What is maximal lactate steady state (MLSS)?

MLSS is the highest constant intensity at which blood lactate stops rising. The standard lab test is several constant-pace runs of at least 30 minutes. Beneke's methodological paper gives the usual criterion: an increase of no more than 1.0 mmol/L after the tenth minute. The fastest pace that passes is the MLSS.

The lactate value at MLSS is individual: in one study of 33 men it averaged 4.9 mmol/L with a standard deviation of 1.4, so a fixed 4 mmol/L line sits above some thresholds and below others. Fixed percentages of maximum heart rate share the problem: a 2020 critique by Jamnick and colleagues concludes that prescribing intensity from a fixed percentage of a maximal value has little merit for producing distinct, domain-specific responses.

How do I find my lactate threshold without a lab test?

Use simple field signs, each with known error. The talk test is the most reliable cheap marker of the first threshold, and a sustained hard effort gives a rough handle on the second. Newer heart-rate methods are promising but need good data and caution.

• LT1 by the talk test. In a study of treadmill and cycle exercise, the point where speech first became difficult was almost exactly at the ventilatory threshold; once speech was no longer comfortable, intensity was consistently above it. Full sentences mean you are below LT1.
• LT2 by a sustained effort. MLSS is usually sustainable for 30 to 60 minutes. The average pace of a hard, even effort that long, such as a well-paced 10K for many runners, gives a rough estimate, close to but not exactly at the threshold.
• LT1 by heart rate variability. DFA a1 measures the pattern in beat-to-beat intervals. In a study of 15 men on a treadmill test, a DFA a1 of 0.75 closely matched the first ventilatory threshold. The recordings came from a lab ECG, the authors warn that artifacts may weaken accuracy, and consumer straps remain an open question.

Field estimates drift with heat, hills, fatigue and a poor night, so many coaches prescribe threshold work by effort and breathing as much as pace.

How do you train your lactate threshold?

Mostly with sustained or broken efforts just below the upper threshold, often called tempo runs or cruise intervals: repeats of a few minutes to ten or more, with short recoveries, at a pace that feels comfortably hard. Repeats bank more threshold time than one continuous run.

A simple first session: ten to fifteen minutes easy, three repeats of eight to ten minutes at a pace you could hold for about an hour with two-minute easy jogs between, then an easy cool-down. It should feel controlled throughout. If the last repeat becomes a fight, the pace was above the threshold. Next time, start a few seconds per kilometer slower.

The best-known modern version is the Norwegian lactate-guided approach: in a 2023 review by Casado and colleagues, its elite runners do three to four lactate-guided threshold interval sessions and one VO2 max session a week, alongside easy running of up to 150 to 180 km a week, with pace held to a lactate target, typically 2 to 4.5 mmol/L, checked every one to three repetitions. It is a system for full-time athletes with blood testing, not a template for five hours a week.

How often should you do threshold runs?

Probably not more than a session a week or so, and not at the expense of easy running. Threshold work is useful and race-specific from 10K to the marathon. But Beneke and colleagues note that the idea that training at threshold intensity is particularly effective has no evidence behind it, and that elite endurance athletes spend 70 to 90 percent of their training below threshold.

For most runners the shape is mostly easy, a little steady, a little hard, and threshold sessions earn their place when the easy running around them is truly easy. The common mistake is every run drifting into a medium effort too hard to recover from and too easy to change much. Busy, not productive.

How does Gears handle this?

Gears doesn't measure lactate or give a threshold number. It coaches in effort gears, personalized running zones placed from your own running and refined by every run with heart rate. On the talk test, Easy (Gear 1) is full sentences, Steady (Gear 2) is short phrases ("Working, but in control.") and Hard (Gear 3) is a few words at most. Pace leads and heart rate guards: on easy or steady stretches, the pace eases when your heart says it is too much.

In Find a run, Lactate threshold is one of 14 training targets, described as "The pace you can hold before the burn builds." Lactate clearance is another. Each run trains exactly one target, and Threshold Cruise is among the preset sessions.

What it doesn't do: estimate LT1, LT2 or critical speed. The gears are personal effort ranges, not lab thresholds; the page on running physiology explains what Gears reads to set them.