FSHP Academy
Exercise Physiology — all lessons

Muscle Physiology

Muscle physiology: excitation–contraction and the sliding filament modelConcentric, eccentric and isometric muscle actionsMotor units, recruitment and rate codingNeuromuscular adaptations to training

Energy Systems

Energy systems overview: how the body makes ATPThe ATP-PC (phosphagen) systemAnaerobic glycolysis and lactateThe aerobic oxidative system

Cardiovascular Physiology

Heart anatomy and the cardiac cycleStroke volume, heart rate and cardiac outputBlood components and oxygen transport

Aerobic Fitness and Intensity

Aerobic fitness concepts and adaptationsVO₂ maxLactate thresholdHeart rate zones and RPE-based intensity control

Lactate threshold

What lactate thresholds are, how they are measured and defined (LT1, LT2, MLSS, critical power), why definitions disagree, and how thresholds anchor endurance training.

Advanced Evidence: Strong evidence 3 min read Reviewed 2026-10-31 Status: draft

Learning objectives

  • Describe the blood lactate response to incremental exercise
  • Distinguish LT1, LT2, MLSS, critical power and fixed-concentration methods
  • Explain why threshold definitions are not interchangeable
  • Use thresholds to set training zones and track adaptation

Before this lesson

Why this matters

Endurance performance depends less on how high your aerobic ceiling is than on how close to it you can work. Lactate thresholds describe that sustainable fraction and anchor training zones.

Fundamental concepts

During an incremental test, blood lactate is sampled at each stage:

Blood lactate response to incremental exercise Blood lactate stays close to resting values (about 1 millimole per litre) at low running speeds, begins to rise at the first lactate threshold (LT1), and rises steeply beyond the second threshold (LT2, close to maximal lactate steady state). A fixed 4 millimole line is shown for comparison; it does not represent the same intensity for every athlete. fixed 4 mmol·L⁻¹ (“OBLA”) LT1 LT2 ≈ MLSS Moderate domain Heavy domain Severe domain 8101214161820 0246810 Running speed (km·h⁻¹) — illustrative trained runner Blood lactate (mmol·L⁻¹)
Figure 1. Schematic blood-lactate curve with the first (LT1) and second (LT2) thresholds separating moderate, heavy and severe intensity domains. — Original diagram, FSHP Academy (schematic, not to scale).
  • LT1 (aerobic threshold) — the first sustained rise above baseline. Below it (moderate domain), lactate and VO₂ quickly stabilise.
  • LT2 / MLSS — the highest intensity at which lactate can be held steady; closely related to critical power/speed. Between LT1 and LT2 (heavy domain), lactate rises then stabilises.
  • Severe domain — above MLSS/critical power: lactate and VO₂ rise until exhaustion (VO₂ “slow component”).

The science: why lactate rises

Lactate in blood reflects the balance between production (rising glycolytic flux, recruitment of type II fibres) and clearance (oxidation, gluconeogenesis). The threshold is not an “anaerobic switch”; the term “anaerobic threshold” has been debated for decades [poole2021].

The definition problem

Reviews have identified many different threshold methods — fixed concentrations (e.g., 2 and 4 mmol/L), baseline + 1 mmol/L, Dmax and its variants, ventilatory thresholds — and these produce different intensities in the same person [faude2009] [jamnick2020]. A fixed 4 mmol/L (“OBLA”) may lie above or below an individual’s MLSS. When comparing tests, always use the same method and protocol.

Performance and training

Joyner and Coyle describe performance velocity as the product of VO₂max, the fraction of VO₂max sustainable (threshold) and economy [joyner2008]. Training shifts the lactate curve to the right — more speed for the same lactate — often more than it raises VO₂max in trained athletes.

Practical application

Common mistakes and misconceptions

Case study

A cyclist’s step test shows LT2 at 245 W and 168 bpm. After 12 weeks of mostly easy riding plus two weekly threshold/VO₂max sessions, LT2 rises to 265 W at a similar heart rate. VO₂max increased only slightly — illustrating why thresholds often track performance better.

Further learning: video lessons

Video links are only marked “verified” after a human has watched them. Unverified entries open a YouTube search for that channel and topic rather than a guessed link.

Introductory needs verification — opens a YouTube search

Lactate threshold explained

Science for Sport

You will understand: what thresholds are and why they matter

Why: Accessible sports-science explanation.
Practical demo needs verification — opens a YouTube search

Lactate testing in the lab — step test protocol

university or sports-institute channels (search)

You will understand: how a lactate step test is run

Why: Seeing the procedure clarifies interpretation.

Knowledge check

Knowledge check · 0/5

1. Maximal lactate steady state (MLSS) is…

Answer A. MLSS is determined from repeated constant-load trials and approximates the heavy–severe boundary.

2. Why is a fixed 4 mmol/L threshold problematic?

Answer B. Individual lactate curves differ; 4 mmol/L may be above or below a person’s MLSS.

3. Above LT2/critical power, VO₂ during constant work…

Answer B. In the severe domain, VO₂ drifts up until max or exhaustion.

4. Endurance training typically shifts the lactate curve…

Answer B. Improved oxidative capacity and lactate clearance shift the curve to the right.

5. Jamnick et al. (2020) concluded that…

Answer B. Their critique highlighted the lack of agreement among methods.

Short-answer & application questions

  1. Sketch and annotate a lactate curve before and after 12 weeks of training.
  2. Explain the moderate, heavy and severe domains and give a training example for each.
  3. Describe a field method to estimate threshold pace and its limitations.

Key takeaways

  • Blood lactate stays near baseline at low intensities, rises above LT1, and rises steeply beyond LT2/MLSS.
  • LT1 and LT2 separate moderate, heavy and severe intensity domains with distinct physiological responses.
  • Dozens of threshold definitions exist; they give different intensities and are not interchangeable.
  • Thresholds improve with training, often more than VO₂max, and are key determinants of endurance performance.

Connected topics

physiology

Heart rate zones and RPE-based intensity control

physiology

The aerobic oxidative system

hybrid training

Zone 2, threshold, VO₂ max and alactic work

hybrid training

Threshold and tempo training

assessment

Cardiorespiratory assessments

References

  1. Faude O, Kindermann W, Meyer T (2009). Lactate threshold concepts: how valid are they?. Sports Medicine, 39(6):469–490. doi:10.2165/00007256-200939060-00003 · PubMed 19453206 Narrative review verified
  2. Jamnick NA, Pettitt RW, Granata C, Pyne DB, Bishop DJ (2020). An examination and critique of current methods to determine exercise intensity. Sports Medicine, 50(10):1729–1756. doi:10.1007/s40279-020-01322-8 Narrative review check pending
  3. Poole DC, Rossiter HB, Brooks GA, Gladden LB (2021). The anaerobic threshold: 50+ years of controversy. Journal of Physiology, 599(3):737–767. doi:10.1113/JP279963 Narrative review check pending
  4. Joyner MJ, Coyle EF (2008). Endurance exercise performance: the physiology of champions. Journal of Physiology, 586(1):35–44. doi:10.1113/jphysiol.2007.143834 Narrative review check pending

Educational content only — not medical advice. Consult a qualified clinician for diagnosis or treatment.