Lactate Threshold: What It Is and What It Predicts

What it is

On a graded test where intensity rises step by step, blood lactate stays near baseline at easy efforts and then climbs. Labs mark that climb in more than one way: a 2009 review located 25 different lactate threshold concepts and described two typical breakpoints, the intensity at which blood lactate first rises above baseline, and the highest intensity at which lactate production and elimination are still in equilibrium, called the maximal lactate steady state¹.

A threshold number means little until you know which concept it comes from, so a figure from one lab, watch or test is not interchangeable with another. Treat any single number as an estimate, and let effort and your own results refine it.

What it predicts

In well-trained runners, a 2022 review concluded that the speed at VO2max seems the best predictor of performance at 1500 m, and that the blood lactate response seems the main predictor from 5000 m up to the ultramarathon². For a 5K to marathon runner, how your blood lactate responds to pace tells you more about the race you can run than VO2max does.

That finding describes who is fastest among well-trained runners. It does not say threshold work is the quickest way for a newer runner to improve: for a newer runner it is more easy running, with harder work in small doses. See the guides on VO2max and running economy for the other two measures that set race speed.

How to train it

Threshold work is sustained running at a comfortably hard effort, where speech is no longer comfortable. It comes in two formats: a tempo run, one continuous stretch, and cruise intervals, blocks of 5 to 15 minutes with a short easy jog or float between. For a 5K or 10K runner a session starts at about 15 minutes of threshold running and builds to 25 to 30 minutes in total. For a half marathon runner it builds from 6 x 5 or 3 x 10 minutes to 40 to 45 minutes in blocks of up to 15 minutes. The guide on tempo and threshold runs covers the sessions.

Run it at threshold or a little under, relaxed, and not over: you recover faster and can repeat it the next week. Count it as one of your one or two hard sessions a week and not an extra on top of them.

Keep it a minority of your running. A 2022 systematic review of 20 articles on middle- and long-distance runners found that the studies with more low-intensity volume, pyramidal or polarized, reported greater improvements than those using a threshold distribution, and suggested at least 70% of volume at low intensity and at most 30% at threshold and high intensity³. The guide on polarized training covers the mix.

How to find yours without a lab

A blood-lactate test is the lab standard, but with 25 concepts in use a single number is an estimate however it is found. One free field check is the talk test. A 2022 review of subjective methods found that the equivocal stage of the talk test, where you are unsure whether speech is still comfortable, reflects the ventilatory threshold, the first breakpoint, while the negative stage (speech not comfortable) and an RPE of 13 to 15 on the 6 to 20 scale reflect the respiratory compensation threshold, the second breakpoint⁴. So the talk test marks the ceiling of easy running at one end and the neighborhood of threshold effort at the other.

Pace is a cruder guide: threshold effort is roughly what you could hold for about an hour of racing, so a recent race result is a starting point.

Runsense reads your lactate threshold heart rate from a hard, steady 30-minute effort and builds your heart rate zones on it (see the guide on testing your LTHR). The guide on heart rate zones covers the bands built on it.