What Is Lactate Threshold? A Runner’s Complete Science Guide

If you’ve been training for a marathon PR, you’ve almost certainly heard of “lactate threshold.” Yet for most runners, it remains one of those terms that’s easy to repeat and hard to truly explain.

When I started running seriously, I knew the term Lactate Threshold (LT) — but I couldn’t have explained what it actually meant or why it mattered.

Lactate threshold is one of the most important factors determining running performance, and a key metric for structuring effective training.

This article gives you a complete breakdown of LT: the key terms, what the numbers actually represent, and how LT relates to your running.

By the end, you’ll have a thorough, working understanding of lactate threshold.

What Is Lactate Threshold?

LT stands for Lactate Threshold — the exercise intensity zone at which blood lactate concentration begins to rise rapidly as you increase effort.

The key point is that lactate threshold is defined by blood lactate values, not by running pace.

A common misconception is treating pace as the definition of LT. Saying “My LT is 6:26/mile (4:00/km)” is not technically correct — LT is determined by blood lactate concentration; the pace that happens to coincide with that threshold is a separate, derived measurement.

Measuring blood lactate requires specialized equipment — a portable lactate analyzer — which most recreational runners don’t own.

I purchased a lactate meter myself to pursue the science of running firsthand. The Arkray Lactate Pro 2 is one of the most widely available options.

Lactate Threshold Is a Zone, Not a Single Point

Lactate threshold represents a zone, not a single fixed point. The graph below plots exercise intensity on the x-axis against blood lactate concentration on the y-axis.

Exercise intensity is often expressed as running pace or heart rate, though neither captures it perfectly — the same pace or heart rate can represent different true intensities depending on how your body is responding that day.

That said, pace and heart rate are the metrics you can track in real time, so they’re widely used as practical proxies for exercise intensity.

As the graph shows, the lactate threshold zone spans blood lactate concentrations of 2.0–4.0 mmol/L. Above this zone, blood lactate rises sharply relative to increases in effort.

Where exactly blood lactate starts to climb rapidly varies by individual. Some runners see the sharp rise begin near 4 mmol/L; others experience it closer to 3.0 mmol/L. Well-trained elite runners tend to have thresholds that shift toward the lower end of that range.

Three related terms you’ll encounter are LT1, LT2, and OBLA (Onset of Blood Lactate Accumulation).

The dual-threshold model of LT1 and LT2 was first proposed by Kindermann et al. (1979) ※1. OBLA was defined by Sjödin & Jacobs (1981) ※2 in a study of Stockholm Marathon runners; running speed at 4 mmol/L blood lactate (VOBLA) was found to explain 92% of the variation in marathon finishing times. You’ll also see LT1 and LT2 referenced widely on social media platforms like X (Twitter) and Instagram.

What Determines Your Lactate Threshold Pace?

Your pace at lactate threshold is determined by two competing rates: how fast your body produces lactate, and how fast it clears it.

Lactate was once considered the cause of fatigue, but modern exercise physiology has overturned that view. Brooks (1986) ※3 proposed the “lactate shuttle” hypothesis, showing that more than 75% of the lactate produced during steady-state exercise is used immediately as fuel during the effort itself. Lactate is generated in active muscles — primarily fast twitch muscle fibers (Type II) — then shuttled to slow twitch fibers, the heart, and the liver, where it is oxidized for energy.

Blood lactate concentration therefore reflects the balance between production and clearance. As exercise intensity rises, lactate production outpaces clearance, and blood lactate climbs. What gets measured is the lactate that spills into the bloodstream.

The faster your mitochondria can recycle lactate — and the faster other tissues can take it up — the less blood lactate accumulates. In practical terms, a higher lactate clearance capacity means a faster pace at threshold.

How Knowing Your LT Makes Training More Efficient

The biggest practical benefit of knowing your LT is that it lets you maximize training volume at intensities that don’t accumulate fatigue.

Seiler (2010) ※4 found that elite endurance athletes perform about 80% of their training sessions at or below 2 mmol/L blood lactate — at or below LT1 — precisely because this intensity allows high volume without carrying fatigue into the next day. A 2025 expert consensus by Sitko et al. ※5 similarly identifies “no residual fatigue the next day” as a defining characteristic of training at or below LT1.

By contrast, training above LT2 demands significantly more recovery time and cannot be repeated at high frequency. Understanding your LT shows you the ceiling of your fatigue-friendly training zone — and that’s where most of your volume should live.

From my own experience, the difference is stark. Sessions held below a certain intensity leave me feeling recovered the next day; push above it and fatigue lingers noticeably.

In concrete numbers, keeping blood lactate at or below 3.5 mmol/L — which for me corresponds to roughly 90% max heart rate — makes a substantial difference in how I feel the next day.

The key takeaway: there is real value in learning, by feel, what intensity ceiling allows your body to recover fully. If you can’t measure blood lactate directly, your subjective effort is your best guide.

How to Find Your Lactate Threshold Pace

When you can’t measure blood lactate directly, there are three practical ways to estimate your LT pace.

Estimate LT Pace from Max Heart Rate

If you know your max heart rate accurately, you can use the percentage-of-max relationship to estimate your LT pace. Heart rate at LT1 through LT2 falls approximately in the range of 82–90% of max heart rate (HRmax). Swain et al. (1994) ※6 showed that 90% HRmax corresponds to roughly 80–82% of VO2 max, which aligns with the range at which LT2 typically occurs (80–90% VO2 max). Keep in mind that the relationship between heart rate and blood lactate varies considerably between individuals.

In my own lactate testing, keeping my heart rate at or below 84% HRmax held blood lactate at or below 2.0 mmol/L, while staying at or below 89% HRmax corresponded to a blood lactate of 4.0 mmol/L.

Estimate LT Pace from Recent Race Results

You can calculate your VDOT from a recent race result and use it to estimate your threshold pace. The graph below shows how race pace relates to blood lactate concentration.

The LT1–LT2 zone corresponds roughly to marathon pace, while LT2 aligns closely with half marathon race pace. Bassett & Howley (2000) ※7 showed that lactate threshold velocity is the best physiological predictor of marathon performance. Sjödin & Jacobs (1981) ※2 demonstrated that OBLA pace — the running speed at which blood lactate reaches 4 mmol/L — explains 92% of the variation in marathon finishing times. In short, your threshold pace falls somewhere between your marathon pace and your half marathon pace.

Estimate LT Pace from Perceived Effort

You can also gauge your LT pace by how hard the effort feels — your rate of perceived exertion (RPE). This method works best when you’ve already calibrated your internal sense of effort against actual data, so treat it as a rough guide.

As noted above, threshold pace corresponds to marathon pace through half marathon pace. The effort you feel in the early miles of a marathon or half marathon is a reasonable proxy for your LT zone.

Focus on the early miles, not the finish — the closing miles of any race feel much harder than threshold truly is. At around 2.0 mmol/L blood lactate, most runners experience almost no sense of exertion at all.

How to Improve Your Lactate Threshold Pace

To run faster at lactate threshold, you need to either reduce how much lactate your body produces at a given pace, or increase how quickly it clears what is produced.

The key player in both processes is the mitochondria. Greater mitochondrial density and higher mitochondrial function means faster glucose uptake and a faster rate of lactate recycling.

Importantly, increasing mitochondrial quantity and improving mitochondrial function require different training approaches. A review by Granata et al. (2018) ※8 found that mitochondrial content depends on training volume, while mitochondrial respiratory function (quality) depends on training intensity. For a deep dive into training your mitochondria, see the related article below.

References

※1 Kindermann W, Simon G, Keul J (1979) “The significance of the aerobic-anaerobic transition for the determination of work load intensities during endurance training” Eur J Appl Physiol Occup Physiol

※2 Sjödin B, Jacobs I (1981) “Onset of blood lactate accumulation and marathon running performance” Int J Sports Med

※3 Brooks GA (1986) “The lactate shuttle during exercise and recovery” Med Sci Sports Exerc

※4 Seiler S (2010) “What is best practice for training intensity and duration distribution in endurance athletes?” Int J Sports Physiol Perform

※5 Sitko S et al. (2025) “What Is ‘Zone 2 Training’?: Experts’ Viewpoint on Definition, Training Methods, and Expected Adaptations” Int J Sports Physiol Perform

※6 Swain DP, Abernathy KS, Smith CS, Lee SJ, Bunn SA (1994) “Target heart rates for the development of cardiorespiratory fitness” Med Sci Sports Exerc

※7 Bassett DR Jr, Howley ET (2000) “Limiting factors for maximum oxygen uptake and determinants of endurance performance” Med Sci Sports Exerc

※8 Granata C, Jamnick NA, Bishop DJ (2018) “Training-Induced Changes in Mitochondrial Content and Respiratory Function in Human Skeletal Muscle” Sports Medicine