Lactate Threshold1 - Defined
When you ask people what is LT1, the answer usually be “The intensity at blood lactate begins to rise”. This intensity is commonly used as a reference for low-intensity or “Zone 2” training.
The challenge is that LT1 is not defined by one universally accepted method. The power or speed assigned to LT1 can change with the test protocol and with the rule used to decide what constitutes a meaningful rise in blood lactate.
INSCYD solves this problem by determining LT1 using a standardized definition, independent of the test protocol, even when no lactate samples are taken.
Blood lactate and LT1
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The First Rise in Lactate
The intuitive concept of the “first rise in lactate” behind the first lactate threshold and the reason it is often used to separate easy endurance exercise from the next intensity domain.
The problem starts when we ask two simple questions: rise compared with what, and by how much?
Where does the first rise start?
The rise of lactate depends on the Test Protocol
Starting intensity, stage duration and the size of each workload increment all affect the lactate values measured at a given point in the test.
Start too high and the first visible increase may already be present in the opening stage. Start sufficiently low with longer stages and lactate may initially fall before it rises.
The result: the first rise of lactate depends on the test protocol, making it nearly impossible to compare values between tests.
One athlete, any protocol, a different answer
Read here as: the first stage whose displayed value is higher than the one before it. It is one rule among several, and they do not all move by the same amount.
Even with a fixed protocol, “the first rise” needs an operational definition: does rise mean the resting value, making LT1 depending in actual nutrition and warm up procedures. Or is the rise compared to the lowest value reached during the test, again making it very dependent on the duration and intensity of the steps in an incremental test.
Then there is measurement precision: lactate analyzers typically can’t measure differences in lactate of < 0.1 mmol/L, while the measurements also contains an error. Depending on the analyzer used this error is in the range of 0.2 – 0.3 mmol/L. Combined this means that a small change on the display may therefore reflect measurement variability rather than a true physiological increase.
In short: to identify LT1, it is not enough to say that lactate has increased. The reference point, minimum meaningful change and measurement uncertainty all need to be defined.
What counts as a real rise?
A Standardized LT1 with INSCYD
INSCYD solves these methodological problems by normalizing LT1 to one standardized definition, regardless of how the athlete was tested.
The LT1 standardized to:
- one protocol: independent of what protocol was used for testing, LT1 is always determined using a six-minute incremental protocol.
- defined lactate increase of 0.45 mmol/L above the lowest lactate concentration. This threshold is designed using the average lactate meter measurement error of 0.35 mmol/L and the resolution of 0.1 mmol/L, ensuring the rise in lactate is above the combination of both: error and resolution.
Because LT1 is derived from the athlete’s physiological profile rather than simply selecting a point from the raw lactate curve, the same standardized definition can be applied to different testing workflows: laboratory lactate tests, field lactate tests and remote performance tests using power or speed. No lactate sampling is required for the remote workflow.
The result is a comparable LT1 value even when the underlying test protocol changes, and access to LT1 even when no lactate test was performed.
Four tests, one normalized lactate curve
Normalized lactate curve accurately calculated from power-duration / speed-duration only
LT1 and Training Prescription
LT1 is widely used to organize endurance-training intensity. In three-zone intensity models, the first lactate commonly defines the boundary between the lowest-intensity domain and the next training zone; recent expert consensus on popular “Zone 2 training” places the target intensity immediately below the first lactate threshold.
If LT1 is used to prescribe training, the accuracy and reproducibility of LT1 directly affect the prescribed power, speed and heart-rate targets. A protocol-dependent or measurement-dependent shift in LT1 can therefore shift the athlete’s training zones even when the athlete’s physiology has not changed.
A standardized LT1 makes longitudinal testing and training prescription comparable: changes in the prescribed training intensity reflect changes in the athlete rather than changes in the testing procedure.
The same athlete, two prescriptions
The range below LT1 is named differently in different zone models, so it carries no zone number here. On a run or a swim test the same shift appears in speed or pace.
The Metabolic Origin of LT1
The blood lactate concentration observed during exercise is the result of lactate appearance and lactate removal. Glycolytic metabolism contributes to lactate production, while oxidative metabolism is a major pathway through which lactate is utilized. LT1 therefore reflects the interaction of multiple physiological characteristics rather than the capacity of one isolated energy system.
With INSCYD this interaction is visualized in the context of VO₂max, VLamax, body composition and, where relevant, exercise economy. Therefore INSCYD does not only provide a standardized way to determine LT1 – independent of testing protocols, but also the physiological context and knowledge why LT1 is at its current value – and more importantly: how to change it.
This provides two levels of information: a standardized LT1 that can be compared across assessments, and the metabolic context needed to understand why LT1 is where it is and why it changes.
What moves the lactate curve and LT1
A higher VO₂max moves the curve and LT1 to a higher intensity, a higher VLamax to a lower one. Body composition is shown as body fat at the same body mass.
Explore other INSCYD metrics.
Oxidative metabolism is a major pathway through which lactate is utilized, so it is one of the characteristics behind where LT1 sits.
Read more VLamaxGlycolytic metabolism contributes to lactate production. Lower it and the first rise in lactate moves to a higher intensity.
Read more Anaerobic Threshold (MLSS)The second threshold: the highest intensity at which lactate production and lactate utilization still hold an equilibrium.
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