Lactate Thresholds — Why It Matters for Athletes

Lactate thresholds — LT1 and LT2 — are key metabolic points that define the boundaries of training zones.

LT1 — First Lactate Threshold

LT1 is the lowest exercise intensity at which a measurable increase in blood lactate concentration is observed compared to resting lactate concentration.

In the context of endurance training, LT1 is marked as the first elevation in lactate concentration above resting levels. This should not be confused with the second lactate threshold, LT2, which occurs at higher exercise intensities.

The first lactate threshold typically averages between 1.3 and 2.5 mmol/L. In most athletes specializing in long-distance races, in our 'TRS Endurance Studio' metabolic tests we observe FatMax at or slightly above LT1.

LT1 is only needed as an indirect marker of fat and carbohydrate expenditure, since nothing fundamentally changes when you run faster or slower than the first threshold. When you train slightly above LT1, lactate concentration will remain in a steady state.

LT2 — Second Lactate Threshold

LT2, on the other hand, is a true 'threshold' because it clearly distinguishes two intensities from each other:

Above LT2 — lactate concentration will rise over time; there is no longer a lactate steady state. The faster your pace above LT2, the quicker you will reach your peak lactate and will have to reduce your pace.

Below LT2 — lactate concentration will not increase over time. A lactate steady state exists. You can run at this intensity for a prolonged period until you become limited by energy availability or other factors, such as electrolyte balance.

With LT1, there is no such clearly visible difference below and above the threshold.

Maximum Lactate Steady State

LT2 is the highest intensity at which muscle and blood lactate can reach a constant concentration, which is why it is commonly referred to as the maximum lactate steady state (MLSS). In other words, it is the point at which the rate of lactate production exactly equals the rate of clearance, where any decrease in intensity will lead to a drop in lactate levels, and any increase in intensity will lead to non-linear lactate accumulation.

You may also see the term 'lactate threshold' used interchangeably with OBLA (onset of blood lactate accumulation), anaerobic threshold, or VT2 (ventilatory threshold). However, all these terms have slightly different meanings due to different measurement methods. In 'classic' terms, for example, the ventilatory threshold, when measured based on RER, should coincide with the lactate threshold, but in practice this rarely occurs, especially in athletes who specialize in various ultra-distances.

The second lactate threshold typically averages between 2.5 and 4.5 mmol/L. On average, you can sustain this intensity for approximately 60–90 minutes based on 'classic' data, but in practice it can be much longer — it all depends on the amount of available energy in the form of carbohydrates.

Training Zones

Looking at the classic 3-zone model, it can be roughly distributed as follows:

Training Zone 1: below LT1 (1–2 mmol/L)
Training Zone 2: between LT1 and LT2 (2–4.5 mmol/L)
Training Zone 3: above LT2 (above 4.5 mmol/L)

In upcoming articles, we will cover self-testing methods and how to determine these thresholds.