Lactate Threshold: What It Is and How to Read It in Your Training Log

What happens to lactate below and above threshold

Resting blood lactate levels are usually in the 1–2 mmol/L range.

When exercising at or below the lactate threshold, lactate produced by muscles is removed without building up in the blood.

At exercise intensities higher than the lactate threshold, lactate production exceeds the rate it can be broken down.

How lactate threshold is measured

Accurate lactate measurement involves taking blood samples (normally a pinprick to the finger, earlobe, or thumb) during a ramp test with progressively increased exercise intensity.

Lactate test strips are coated with lactate oxidase which converts lactate to pyruvate, producing hydrogen peroxide as a byproduct.

The hydrogen peroxide produced in the strip reaction is oxidized to hydrogen ions, oxygen, and electrons, and the strip electrodes measure the resulting current to estimate blood lactate.

Blood lactate sample results can vary based on individual health status, glycogen status, ambient temperature, sampling site, sweat contamination, and the accuracy of the lactate analyzer.

Near-Infrared Spectroscopy (NIRS) sensors measuring muscle oxygen saturation (SmO2) are used as a non-invasive proxy for determining physiological thresholds and training zones.

How endurance training relates to lactate threshold

Regular endurance exercise raises the exercise intensity at which lactate levels will rise.

Training adaptations that raise the lactate threshold are mediated via activation of PGC-1α.

PGC-1α activation alters the isoenzyme composition of the lactate dehydrogenase (LDH) complex.

PGC-1α activation decreases LDHA activity while increasing LDHB activity.

Aerobic training increases the lactate threshold but does not increase lactic acid tolerance.

Anaerobic training increases tolerance of the effects of lactic acid over time.

Interval, fartlek, and energy systems around threshold

Interval training alternates work and rest periods allowing the body to temporarily exceed the lactate threshold and then recover to reduce blood lactate.

Interval training during high intensity exercise uses the ATP-PC and lactic acid energy systems.

Fartlek training combines continuous aerobic and interval anaerobic elements with consistent changes of pace and intensity.

Using lactate threshold ideas to read today’s workout

The lactate threshold is a useful measure for deciding exercise intensity for training and racing in endurance sports such as long distance running, cycling, rowing, long distance swimming, and cross country skiing, so it can also organize how you look back at sessions in your log.

In zone-based polarized training, LT1 is linked to an inflection often observed around 2.0 mmol/L, so efforts clearly easier than this point can be grouped together when you review easy days.

In the same approach, LT2 is linked to an inflection often observed around 4.0 mmol/L, so you can tag sessions or intervals you expect to be around or above this level as your most demanding work when you summarize the week.

Polarized training descriptions that allocate about 80 percent of weekly volume below LT1 and a smaller share above LT2 give you a template to compare with your actual distribution without treating it as a prescription.

Practical record-checking tasks to try

The following are optional exercises you can try to better understand your own data and notes around lactate and intensity.

• If you have access to appropriate equipment, you can measure and record resting blood lactate to compare with the typical 1–2 mmol/L resting range. Try this on different days and note date, time, and conditions.
• If supervised testing is available, you can perform a progressive ramp exercise test with periodic blood samples from the finger, earlobe, or thumb to observe where lactate begins to rise. Record the workload, heart rate, and lactate at each step.
• You can compare blood lactate results to the corresponding heart rate and your perceived exertion to identify approximate LT, AeT, and AnT points in your notes, using the definitions based on rises above resting levels and inflection points around 2 mmol/L and 4 mmol/L where applicable.
• When planning an interval session, you can design work periods that you expect to be above your estimated lactate threshold with recovery periods you expect to be below it, then record how lactate or perceived recovery changes between intervals.
• You can try a fartlek session with varied pace and then write down how the changes of intensity felt compared to steady efforts, noting any segments you suspect approached OBLA or LT2 based on effort and, if available, lactate readings near 4 mmol/L.
• If you use a NIRS SmO2 sensor, you can log muscle oxygen saturation alongside occasional blood lactate samples to explore how muscle oxygen dynamics correspond to lactate-based thresholds and zones in your own data.
• On test days, you can track factors that may affect lactate readings—such as prior glycogen status, ambient temperature, sampling site, and possible sweat contamination—and add brief notes about them next to each result.
• Looking at a week or more of training, you can map your estimated time below LT1 and above LT2 to see how your own distribution compares with the approximate 80 percent below LT1 pattern described for polarized training, without assuming that any specific percentage is required for you.

Use these tasks as ways to learn how your current logs, units, and notes line up with concepts like LT, AeT, AnT, OBLA, LT1, and LT2, and adjust how you record sessions if any important details are missing.

This article is general health information and is not a substitute for medical diagnosis or treatment. Consult a healthcare professional if you have concerns.