Key takeaways
- Lactate threshold (LT) is the intensity where blood lactate rises faster than the body can clear it.
- It marks the shift from a sustainable pace to one causing rapid fatigue.
- It's roughly the fastest pace you can hold for about an hour — a key endurance marker.
- It's highly trainable, and a central target of tempo and threshold workouts.
What lactate threshold is
Lactate threshold (LT) is the exercise intensity at which lactate begins to accumulate in the blood faster than the body can clear it, marking the transition from a pace you can sustain for a long time to one that leads to rapid fatigue. It roughly corresponds to the fastest pace you can hold for about an hour.
Why it matters
It strongly determines sustained endurance speed. Two runners with similar VO2 max can perform very differently based on the pace they hold at threshold — a higher LT means you run faster before fatigue-inducing lactate accumulation kicks in. Raising threshold pace is one of the most impactful ways to improve distance performance.
A runner does weekly tempo runs at a ‘comfortably hard’ effort they could just hold for an hour — right at their lactate threshold. Over a season, that same effort yields a noticeably faster pace, meaning their threshold has shifted up and they can race faster before tiring.
How to train it
Mainly with tempo runs and threshold workouts — sustained or interval efforts at or near threshold pace (a ‘comfortably hard’ intensity holdable for ~an hour). These teach the body to clear lactate more efficiently and push the threshold to a faster pace, built on the aerobic base of Zone 2 easy running. It’s distinct from VO2 max (your aerobic ceiling), which intervals target.
The bottom line
Lactate threshold is the intensity where lactate accumulates faster than your body can clear it — the line between a sustainable pace and rapid fatigue, roughly your best one-hour effort. Because it strongly determines sustained endurance speed, raising it is one of the most impactful training goals, trained through tempo and threshold workouts on a solid aerobic base.
Frequently asked questions
What is lactate threshold?
Lactate threshold is the exercise intensity at which lactate (a byproduct of energy metabolism) starts building up in the blood faster than your body can clear it. Below the threshold, your body keeps lactate in balance and you can sustain the effort for a long time; above it, lactate accumulates rapidly and fatigue sets in quickly. It roughly corresponds to the hardest pace you can hold for about an hour.
Why does lactate threshold matter for endurance?
Because it strongly determines how fast you can go in sustained endurance events. Two runners with similar VO2 max can perform very differently based on the pace they can hold at threshold — a higher lactate threshold means you can run faster before fatigue-inducing lactate accumulation kicks in. Raising your threshold pace is one of the most impactful ways to improve distance-running performance, which is why it's a central training focus.
How do you train lactate threshold?
Mainly with tempo runs and threshold workouts — sustained or interval efforts at or near your threshold pace/effort (a 'comfortably hard' intensity you could hold for roughly an hour). These workouts teach your body to clear lactate more efficiently and shift the threshold to a faster pace. A strong aerobic base from easy and long runs supports this. Over time, threshold training lets you sustain faster paces for longer, improving race performance across endurance distances.
Sources
- Exercise physiology — American Council on Exercise
- Endurance training — American College of Sports Medicine