What is lactate threshold?
Exercise physiologists describe two lactate thresholds during a hard effort. LT1, the aerobic threshold, is where blood lactate first rises above resting levels, per Faude, Kindermann and Meyer's 2009 review in Sports Medicine. LT2, the anaerobic threshold or maximal lactate steady state (MLSS), is the hardest effort at which lactate production and clearance stay balanced, the same review's second breakpoint. A third marker, OBLA, uses a fixed 4 mmol/L blood-lactate reading as a practical stand-in for LT2. As a rough field approximation, McMillan Running describes LT2 pace as close to what a runner could hold for about an hour of racing.
Garmin and Coros watches surface a lactate threshold number without explaining where it comes from, and the term covers at least three related but distinct ideas. Below is what each one measures, roughly how hard and how long it corresponds to, and how it gets tested.
LT1, LT2/MLSS and OBLA compared
This table is Runked's own, built around Faude, Kindermann and Meyer's 2009 review and the two lactate breakpoints it describes, plus field methods from RunnersConnect and Marathon Handbook. None of the numbers below substitute for a lab test.
| Term | Definition | Typical effort / duration | How it's measured |
|---|---|---|---|
| LT1 (aerobic threshold) | Where blood lactate first rises above its resting baseline during a graded effort test (Faude et al. 2009). | Conversational; close to the easy end of the effort scale covered in Runked's zone 2 guide. | Blood lactate sampled at each stage of a graded test; LT1 is the point where the value leaves baseline (Faude et al. 2009). |
| LT2 (anaerobic threshold / MLSS) | The highest effort at which lactate production and clearance stay in balance, the review's second breakpoint (Faude et al. 2009). | Comfortably hard. McMillan Running's approximation places it close to one-hour race effort; RunnersConnect describes a similar range of roughly 45 to 60 minutes. | Directly, by testing whether a pace holds a steady lactate reading, or estimated from a recent 10-mile or half-marathon time, a 30-minute all-out time trial, or a step test (RunnersConnect). |
| OBLA (fixed 4 mmol/L) | A fixed blood-lactate reading of 4 mmol/L reached during a graded test, used as a standardized stand-in for LT2; Faude et al. 2009's review groups this with other fixed-concentration methods, separate from the breakpoint-based LT1 and LT2 above. Marathon Handbook uses the same 4 mmol/L mark as its working definition of threshold. | Built to sit near LT2; Faude et al. 2009's review notes that how closely this fixed mark tracks an individual's directly tested MLSS is rarely reported in the literature, so it's best used as a rough estimate. | The pace or power at which blood lactate crosses 4 mmol/L during a single graded test. |
Why it's tracked separately from VO2 max
Joyner and Coyle's 2008 review, Endurance exercise performance: the physiology of champions, in The Journal of Physiology, names VO2 max, lactate threshold and running economy as three separate physiological factors that together determine endurance performance. Lactate threshold interacts with VO2 max to set the highest oxygen consumption, and the pace built on it, a runner can hold for a race of a given length; two runners with the same VO2 max can still hold different race paces if their thresholds sit at different fractions of that ceiling. Runked's VO2 max guide covers that ceiling in more depth.
Faude, Kindermann and Meyer's 2009 review opens by noting that "blood lactate curve and lactate thresholds (LTs) have become important in the diagnosis of endurance performance" across nearly 50 years of research, and its own analysis found "strong linear correlations, particularly for running events" between lactate threshold measures and endurance performance, across the 32 studies it evaluated. A correlation across studies does not settle what any single runner's number means: the review counts 25 different lactate threshold concepts still in use, and its own conclusion argues for folding them into one broader "aerobic-anaerobic transition" framework.
How to use it in training
Runked's running workouts guide covers building tempo runs and cruise intervals, both LT2-effort sessions, into a week alongside easy days. Three free ways to estimate LT2 pace, per RunnersConnect: a recent 10-mile or half-marathon time, a 30-minute all-out time trial, checking average heart rate over the final 20 minutes and taking average pace across the effort as a working estimate of threshold pace, or a step test. As a rough approximation, McMillan Running places LT2 pace close to what a runner could hold for about an hour of racing. None of these three match a lab test exactly, and Faude et al. 2009's review notes that how well a fixed approximation tracks a directly tested MLSS for a given person is rarely reported in the literature.
LT1, the lower and easier threshold, sits close to the conversational effort Runked's zone 2 guide covers in more detail; that guide's heart-rate and talk-test methods for finding an easy pace apply here too.
Common mistakes
- Running every threshold session all-out. Marathon Handbook's guide warns that "doing too much too soon can lead to overtraining and may cause more fatigue than positive physiological adaptations." Two focused sessions a week is what Runked's running workouts guide recommends for mixing hard and easy days.
- Treating the 4 mmol/L OBLA mark as an exact personal number. Faude et al. 2009's review notes that how well this fixed mark tracks a directly tested MLSS for a given person is rarely reported in the literature, so a watch or lab reading at 4 mmol/L is best treated as an approximation.
- Confusing lactate threshold with VO2 max. Joyner and Coyle's 2008 review lists them as separate factors: two runners can share a VO2 max and still hold different threshold paces.
- Chasing a single number instead of a multi-week trend. A watch's threshold estimate, like its VO2 max estimate, moves around week to week; Runked's VO2 max guide covers how much watch-based estimates can vary.
None of this is medical advice. Talk to a doctor before adding hard threshold sessions if you have a heart condition, chest pain, dizziness during exercise, or you're new to structured training altogether.
What to do next
Runked's running workouts guide covers tempo runs, cruise intervals and how to fit them around easy days. The zone 2 guide covers the easier end of the effort scale, close to LT1. The VO2 max guide covers the other ceiling Joyner and Coyle's review names alongside lactate threshold. And for a first race built around one of these efforts, Runked's guide to pacing your first race covers turning a threshold or tempo pace into an actual race plan.
Compare threshold numbers to your own trend, not to other runners: in Runked, the rank starts everyone at Bronze and only moves on your own runs. See how the running rank works.
Find out where you stand
Runked is free on the App Store. Connect your watch or track 3 runs, and meet your Runk.
Download on App StoreFrequently asked questions
What is a normal lactate threshold?
There is not one normal number. Lactate threshold can be reported as a pace, a heart rate, or a percentage of VO2 max, and each shifts with a runner's fitness and the specific test used. Faude, Kindermann and Meyer's 2009 review found strong correlations between different lactate threshold measures and race performance, especially in running, but the same review lists 25 different ways researchers have defined the threshold, so two labs testing the same runner can report different numbers.
What is the difference between LT1 and LT2?
LT1, the aerobic threshold, is where blood lactate first rises above its resting baseline during a graded effort test, per Faude, Kindermann and Meyer's 2009 review. LT2, the anaerobic threshold or maximal lactate steady state (MLSS), is the hardest effort at which lactate production and clearance stay in balance, the same review's second breakpoint. LT1 sits close to the easy, conversational effort covered in Runked's zone 2 guide; LT2 sits close to a tempo run, covered in Runked's running workouts guide.
How is lactate threshold different from VO2 max?
Joyner and Coyle's 2008 review in The Journal of Physiology names VO2 max, lactate threshold and running economy as three separate physiological factors that together determine endurance performance. VO2 max sets a ceiling on how much oxygen a runner can use at full effort; lactate threshold sets how much of that ceiling the runner can actually hold during a race. Runked's VO2 max guide covers the ceiling itself.
Does Runked measure lactate threshold?
No. Runked does not test blood lactate. Runked PRO's Runner DNA scores six dimensions, Endurance, Pacing, Speed, Consistency, Climbing and Threshold, none of which is a direct lactate measurement.