If you’ve worked with endurance athletes or run tests in a performance lab, you’ve likely come across Lactate Threshold 1 (LT1). In this article, we’ll delve into LT1 by unpacking the most common misconceptions and pitfalls about it and how to avoid them. Plus, don’t miss the video where Sebastian Weber explains these common mistakes in detail.

1. What Exactly Is LT1?

LT1 is traditionally defined as the first increase in blood lactate concentration above a baseline level. Lactate threshold 1 is most commonly determined during an incremental exercise test—where you gradually increase speed or power in steps, measuring lactate at the end of each stage.

However, as straightforward as “first rise” sounds, practical challenges arise:

  • Baseline Confusion: Is it a rise above resting lactate or above the minimum lactate measured during the test?
  • Measurement Error: The accuracy and measurement resolution of the lactate measurement device determines if a change in lactate concentration can be interpreted as a true increase or needs to be accounted for by inaccuracy of measurement. Handheld lactate meters can have an error margin of up to ±0.5 mmol/L, which complicates identifying small increases.
  • Protocol Dependency: Step durations (e.g., 3-minute vs. 6-minute stages) and initial load will profoundly alter lactate concentrations.

2. The Impact of Step Duration

One of the most overlooked aspects of determining LT1 is how long each stage in the test lasts:

Shorter Steps

  • The athlete doesn’t stay at each power or speed long enough to reach a steady lactate equilibrium.
  • There is less time per step to accumulate lactate (at high intensities) or to clear it (at low intensities)
  • Lactate levels ramp up later and more gradually.

Longer Steps

  • Allow more time for lactate clearance at low intensities, often revealing a more pronounced dip in lactate below resting values.
  • Lead to a steeper and earlier increase in lactate once the load passes a certain point.
example of 3 lactate curves of the same athlete - just using different step duration and resting lactate concentration
Here is an example of 3 lactate curves of the same athlete – just using different step duration and resting lactate concentration. Where do you mark the LT1 intensity?

In practical terms, if you’re comparing two lactate profiles from different labs or different testing protocols, you may well be comparing apples to oranges. 

3. LT1 Is Not the Same as FatMax

A common misconception—especially among athletes diving into Zone 2 training—is to assume that LT1 perfectly aligns with the intensity where you burn the most fat (often referred to as “FatMax”). While both occur below the anaerobic threshold (LT2), they do not necessarily coincide.

  • FatMax: The exercise intensity at which the body’s rate of fat oxidation rate peaks.
  • LT1: The first rise in lactate above the baseline or minimal measured value.

Because the intensity at which FatMax occurs is highly individual—depending on factors like VO2max, glycolytic rate (VLamax) —it rarely lines up precisely with the first lactate surge.

How to Avoid These Pitfalls

Below, we present a standardized method that addresses inconsistent protocols, lactate meter inaccuracies, and the need for lactate testing itself. By unifying these factors, you can ensure your LT1 determinations remain reliable and comparable across different test settings.

Standardizing Protocols—Inside the Algorithm

INSCYD applies a fixed reference step duration (6 minutes), resting lactate value, and measurement tolerance within its software’s algorithm! That means:

  • You can use different step durations (3, 5, 6 minutes, etc.) in the field or lab.
  • INSCYD automatically recalculates your data as if it were a standardized 6-minute test, including a baseline of 1.25 mmol/L (or comparable reference) and an error margin for handheld meters.
  • Result: You get an LT1 determination that is protocol-independent and reproducible across different testing environments.

This is especially beneficial when combining lab testing (with or without lactate samples) and field testing—LT1 remains comparable, thanks to the internal standardization.

Factoring in Lactate Meter Errors (When You Do Use One)

Handheld lactate meters can be invaluable, but any small jump (e.g., 0.1 or 0.2 mmol/L) might be smaller than the device’s margin of error:

  • INSCYD incorporates per default typical ±0.35 mmol/L measurement error plus the device’s resolution (e.g., 0.1 mmol/L)  – or the typical measurement error and resolution of your specific device which you used.
  • This ensures that an increase must be large enough to exceed the “noise floor” before declaring a true rise in lactate concentration.
INSCYD Lactate Threshold 1 Graph

Determining FatMax and LT1 from the Same Test

No separate test needed—INSCYD analyzes your data (lab or field, with or without lactate) to produce:

—all from the same test. This ensures you see how LT1 correlates (or not) with FatMax, while also forming a complete metabolic profile.

LT1 offers a foundation for zone-based training, yet it’s more than a single number. It’s part of a bigger metabolic puzzle that includes VO₂max, VLamax, and other physiological markers.

INSCYD provides you with a 360-degree view of the athlete’s performance, ensuring you capture all the metrics needed to enhance aerobic efficiency or shift your fat-burning capabilities. By planning training around these collective metrics, you can tap into the full potential of your athlete’s metabolic profile.

LT1 and other metrics

You Don’t Need a Lactate Meter to Determine LT1 Anymore

Before, LT1 was only accessible by measuring blood lactate. If you weren’t doing lactate tests, you simply couldn’t obtain this critical metric. This creates challenges when:

  • Athletes are remote, making regular finger-prick measurements impractical.
  • Lack of lab equipment or handheld meters.
  • The cost and time investment of repeated lactate tests deter frequent assessments.

As a result, many coaches and athletes who can’t perform lactate tests end up without any LT1 data at all—leaving them with no reliable benchmark for lower-intensity training zones and missing out on key insights that could guide more effective endurance development.

Now, for coaches who lack easy access to lab equipment or prefer remote testing, the INSCYD Power Performance Decoder generates a lactate curve from: a series of three short maximal efforts in cycling or running – using Power output (cycling) or GPS speed (running) only. Here’s how it works:

Instructions of Power-Performance Decoder

Because the algorithm is standardized internally, you’ll receive an LT1 determination plus the other vital metrics (VO2max, VLamax, FatMax) without taking any blood samples. This uncouples LT1 from invasive testing or specialized lab gear, reducing cost and logistical hurdles.

Putting It All Together

LT1 remains a valuable benchmark in endurance training, but—like every metric—it has nuances and limitations

The “first increase in lactate concentration” depends on baseline assumptions, test protocols, and measurement error. It also doesn’t perfectly overlap with maximum fat oxidation, nor does it require invasive testing if you use the right performance analysis tools.

By recognizing these intricacies, coaches and lab professionals can:

  • Avoid false comparisons when protocols differ.
  • Provide athletes with accurate, data-driven insights on training intensities.
  • Use LT1 in tandem with other physiological markers—such as FatMax, VLamax, and VO2max—to create a more holistic training.

Most importantly, a clearer understanding of LT1 empowers you to guide athletes toward smarter, more efficient endurance training—where all the puzzle pieces fit together.

👉 If you’re interested in learning more, download our free whitepaper: A Unified Definition of and Determination of the First Lactate Threshold (LT1).

Ready to Standardize Your LT1 Approach?

If your coaching or lab environment needs a more consistent and physiology-backed definition of LT1, try INSCYD. 

By leveraging a standardized protocol—complete with explicit factors for measurement error—coaches and labs can provide athletes with an accurate, actionable and reproducible measurement – which is the foundation to create training prescriptions and monitor progress.

By refining how we determine LT1, we not only reduce confusion but also open the door to more targeted and productive training interventions. Ultimately, understanding LT1 is about helping athletes train smarter—and seeing tangible progress where it matters most: in their performance.

Now get LT1—whether you perform lactate testing or not

Access this critical metric not only through lab or field lactate tests but also using remote testing measuring power or speed-only—no lactate sampling required!

  • No lactate testing required
  • Works Across All Endurance Sports
  • Protocol Independent
  • Enhanced training zones
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