Lactate threshold is the exercise intensity at which the rate of lactate production in working muscles begins to exceed the rate of clearance. Below this threshold, lactate is produced continuously but cleared efficiently, keeping blood lactate near resting levels. Above it, lactate accumulates progressively.
The lactate threshold corresponds roughly to the fastest pace you can sustain for approximately 30–60 minutes — what many runners call "tempo pace." It typically occurs at 80–90% of VO2 max in well-trained runners, and at a lower percentage in less-trained individuals.
There are actually two threshold concepts commonly referenced: - LT1 (first lactate threshold / aerobic threshold): the point where lactate first begins to rise above baseline, typically around 65–75% VO2 max. Below this, fat is the primary fuel. - LT2 (second lactate threshold / lactate threshold): the point of rapid accumulation, where the sustainable aerobic ceiling is. This is typically what coaches mean when they say "threshold pace."
Why it matters for running: the lactate threshold determines how fast you can sustain a hard effort. Two runners with identical VO2 max but different lactate thresholds will perform very differently at distance — the runner with a higher threshold can sustain a higher percentage of their VO2 max, which translates directly to faster race pace.
Estimating LT without a lab: the simplest field estimate is from race performance. In the Daniels framework, threshold pace corresponds approximately to your best 10K pace or slightly slower (the pace you could sustain for 30–60 minutes if running to the limit). The VDOT calculator shows threshold pace derived from your race time.