What Is Lactate Threshold and Why Should Runners Care?

Of all the physiological concepts that underpin endurance performance, lactate threshold is the one that correlates most strongly with race performance across distances from 5k to the marathon. Yet it remains poorly understood by most recreational athletes, who often confuse it with maximum effort, anaerobic threshold, or simply 'the point where it starts hurting'.

Understanding lactate threshold properly - what it is, where yours sits, and how to develop it - is one of the most valuable things an endurance athlete can do for their long-term performance.

What Lactate Actually Is

Lactate is a byproduct of carbohydrate metabolism. When your muscles break down glycogen to produce energy, lactate is produced as part of that process. At low intensities, the body produces lactate slowly enough that it can be cleared and recycled as fuel as fast as it is produced. The blood lactate level remains relatively stable.

As intensity increases, lactate production accelerates. At some point - the lactate threshold - production begins to outpace clearance. Blood lactate levels start to rise. The body's buffering systems can manage this for a limited period, but beyond a certain concentration, the environment in the working muscles becomes increasingly hostile to sustained effort.

The practical consequence is that intensity cannot be sustained indefinitely above the lactate threshold. The question is not whether you will slow down, it is when.

Lactate Threshold vs Anaerobic Threshold: Clearing Up the Confusion

These terms are often used interchangeably, which causes confusion. Strictly speaking, they describe slightly different points on the intensity curve. Lactate threshold (LT1) is the first point where blood lactate rises meaningfully above resting levels - this corresponds to a relatively moderate intensity and is associated with the upper boundary of Zone 2.

What coaches and athletes typically refer to as 'threshold' in training is better described as the lactate turn point or LT2 - the intensity at which lactate accumulation accelerates sharply. This is the pace you can sustain for approximately 40 to 60 minutes of maximal effort. TrainingPeaks and most structured coaching frameworks anchor training zones to this second threshold point.

For practical training purposes, when a coach prescribes 'threshold running', they mean running at or slightly below the intensity at which lactate begins to accumulate rapidly - the pace that is comfortably hard rather than simply hard.

Why Threshold Is So Important for Race Performance

The relationship between lactate threshold pace and race performance is consistent and well-established. The faster your threshold pace, the faster you can run while remaining below the point of rapid lactate accumulation, the faster your sustainable race pace will be across virtually every endurance distance.

For a half marathon runner, threshold pace is typically around 20 to 30 seconds per kilometre faster than race pace. For a marathon runner, threshold pace is typically 30 to 50 seconds per kilometre faster than race pace. Developing threshold pace directly translates to faster race performances.

How to Find Your Threshold

The most precise method is a laboratory lactate test, where blood samples are taken at incremental intensities to plot the lactate curve. This is accurate but expensive and not practically available to most amateur athletes.

A reliable field-based alternative is a 30-minute time trial. After a proper warm-up, run for 30 minutes at the fastest sustained effort you can maintain for the full duration. Record your average heart rate for the final 20 minutes. That heart rate is a close approximation of your lactate threshold heart rate, and your average pace for the final 20 minutes approximates your threshold pace.

The Performance Lab Lite session at stevebarbour.com provides a structured field assessment that establishes both threshold pace and heart rate zones from a single test protocol.

How to Train Lactate Threshold

Threshold training means spending meaningful time at or just below threshold intensity. The most common formats are tempo runs and cruise intervals.

A tempo run is a sustained continuous effort at threshold pace for 20 to 40 minutes, following an easy warm-up. The pace should feel comfortably hard - you can speak single words but not full sentences. If you can hold a conversation, you are below threshold. If you cannot speak at all, you have gone above it.

Cruise intervals are repeated shorter efforts at threshold pace with brief recovery periods - typically 5 to 8 minutes at threshold with 60 to 90 seconds of easy jogging recovery, repeated four to six times. The recovery is short enough that lactate remains elevated, producing a similar adaptation to a sustained tempo run but broken into more manageable segments.

Threshold sessions should appear in a training week no more than once or twice, with adequate easy running on the days surrounding them. Threshold training generates significant fatigue, and too much of it without recovery undermines the adaptation it is trying to create.

Key Takeaways

Lactate threshold is the physiological ceiling of sustainable effort. Raising that ceiling, through consistent, well-structured threshold training on top of a solid aerobic base, is the most direct path to faster race times at every endurance distance. Know where your threshold sits. Train it consistently. And keep the surrounding easy running genuinely easy.

Steve Barbour is a UK-based online running and triathlon coach. The Performance Lab Lite session at stevebarbour.com/coaching includes a field-based threshold assessment to calibrate your training zones properly.