What is Anaerobic threshold?

What is Anaerobic threshold?

The anaerobic threshold is the intensity at which your body can no longer clear blood lactate as fast as your working muscles produce it, so lactate begins to climb and hard effort starts to feel unsustainable. In everyday training language it is the pace or power you can hold at a comfortably hard, controlled ceiling, roughly the effort of a 30 to 60 minute race.

In most textbooks and testing labs the phrase is used interchangeably with lactate threshold, and for practical training that shorthand is fine. There is an honest caveat, though. The word anaerobic implies your muscles have run out of oxygen and switched to oxygen-free metabolism, and that is not what happens. Oxygen is still being used the whole time.

What changes is the balance between how fast lactate is made and how fast it is removed and reused. Because of that, many exercise physiologists now prefer lactate threshold as the more accurate label. You will still see anaerobic threshold everywhere on treadmills, cycling head units, and lab reports, so it is worth knowing exactly what it does and does not mean. Whatever you call it, this transition point is one of the strongest predictors of endurance performance, often a better predictor than VO2 max, because it sets the highest intensity you can actually hold for a long time.

How it works

The anaerobic threshold works through the balance between lactate production and lactate clearance. Your muscles constantly break down glucose for fuel, and that process produces lactate even at rest and at easy paces, all with plenty of oxygen present. At low intensities your body clears and reuses that lactate as fast as it appears through the heart, liver, and slow-twitch muscle fibers, so blood lactate stays low and flat.

As you speed up, you recruit more fast-twitch fibers and burn more glucose, so lactate production rises. Below threshold, clearance keeps pace and lactate holds steady. At the anaerobic threshold, production overtakes clearance, and blood lactate begins to rise sharply rather than plateau. The hydrogen ions released alongside lactate raise acidity, which the body buffers by producing extra carbon dioxide; you blow that off by breathing harder, which is why ventilation spikes at a similar intensity, the point Karlman Wasserman first used in the 1960s to estimate the threshold from breathing gases.

This is the mechanism behind that unmistakable moment in a hard effort when your breathing turns ragged and the pace suddenly feels like it is fighting back. Training raises the threshold by building more mitochondria, capillaries, and lactate-clearing transporters, so you can hold a higher pace before production outruns removal.

The scale

There is no single equation for the anaerobic threshold; it is read from a test. The reference markers below define the aerobic-anaerobic transition. OBLA (onset of blood lactate accumulation) at 4 mmol/L is the classic fixed marker for the anaerobic threshold, though the true value is individual.

How to apply it

• Blood lactate step test: The lab reference method. You ride or run at rising stages while a technician takes a fingertip blood drop each stage. Plotting lactate against pace reveals the sharp upturn, and the 4 mmol/L point is read off as the anaerobic threshold.
• Gas exchange (ventilatory) test: A mask measures oxygen and carbon dioxide during a ramp test. The second ventilatory threshold, where breathing rises steeply to buffer acidity, closely tracks the anaerobic threshold. This is the original Wasserman method and needs no blood.
• Field threshold test: Without a lab, a maximal 30-minute time trial estimates threshold well: your average heart rate over the final 20 minutes approximates threshold heart rate, and your average pace or power approximates threshold pace. Critical speed and FTP tests use the same idea.
• Tempo and threshold runs: To raise the threshold, train at or just below it for sustained blocks: 20 to 40 minutes of comfortably hard tempo running or 2 to 4 by 8 to 15 minute cruise intervals. This teaches the body to produce less lactate and clear more at a given pace.
• VO2 max intervals: Harder intervals above threshold, such as 4 to 6 by 3 to 5 minutes near VO2 max effort with equal recovery, lift the ceiling the threshold sits under. A bigger aerobic engine gives the threshold more room to rise across a season.
• High aerobic base volume: Most weekly training should sit well below threshold in easy zone 2. That large volume of low-intensity work builds the mitochondria and capillaries that do the lactate clearing, which is what ultimately pushes the threshold to a higher pace.

Worked example

Here is a simplified lactate step test for a recreational runner. She runs four-minute stages at rising speeds while blood lactate is sampled after each. The anaerobic threshold is read where lactate crosses roughly 4 mmol/L and starts climbing steeply, which here lands between the 13 and 14 km/h stages.

Her anaerobic threshold pace sits near 13.5 km/h. Training goal: after a block of tempo work and base volume, the whole curve shifts right, so 14 km/h now produces only 3 mmol/L and she can race faster at the same internal effort.

Anaerobic threshold vs lactate threshold

For everyday training the two terms point to the same comfortably-hard ceiling, so using them interchangeably rarely causes problems. Lactate threshold is the more correct label because there is no intensity at which muscles stop using oxygen.

By goal

• Beginners and general fitness: You do not need lab numbers. Use the talk test: your threshold is roughly the effort where you can only speak a few words at a time. Spend most sessions easier than that, and add one comfortably-hard tempo effort a week to nudge the threshold up.
• Endurance athletes: Threshold is your key race predictor for 10 km through the marathon. Test it two or three times a season, train tempo and cruise intervals at threshold pace, and pair them with high easy volume so the whole lactate curve shifts to a faster pace.
• Team-sport and strength athletes: A higher anaerobic threshold means you recover faster between sprints and hold work capacity late in a game or session. Two aerobic base sessions plus one threshold interval workout a week raises your ceiling without eating into strength training recovery.

Common misconceptions

• "At the anaerobic threshold your muscles stop using oxygen and switch to anaerobic metabolism." Oxygen is used continuously through the whole effort, including above threshold. Lactate is produced at every intensity, even at rest, under fully aerobic conditions. What changes at the threshold is the balance between lactate production and clearance, not the presence of oxygen. This is why physiologists such as George Brooks argue the term anaerobic threshold is inaccurate.
• "The anaerobic threshold is a single exact point that is identical for everyone at 4 mmol/L." The 4 mmol/L OBLA figure is a convenient fixed convention, not a universal truth. The real threshold varies between people and shifts with training, diet, and glycogen status. Some athletes hold steady lactate above 4 mmol/L and others below, so individual testing beats a fixed number.
• "Lactic acid causes the burn and is a waste product that limits you at threshold." Lactate itself is a valuable fuel that the heart and muscles reuse for energy. The burning feeling comes from accumulating hydrogen ions and other metabolites, not from lactate directly. Blood lactate is a marker of intensity, not the cause of fatigue, and higher clearance is a sign of better fitness.
• "Anaerobic threshold and lactate threshold mean different physical things." They describe the same transition from opposite measurement traditions: gas exchange versus blood lactate. In practice they land at nearly the same intensity, so the labels are used interchangeably. Lactate threshold is simply the more accurate name because it makes no false claim about oxygen use.

Related terms

Anaerobic threshold FAQ

What is the anaerobic threshold in simple terms?

The anaerobic threshold is the hardest effort you can hold for a long time before lactate builds up and the pace becomes unsustainable. It feels comfortably hard, roughly the effort of a 30 to 60 minute race, where you can only speak a few words at a time between breaths.

Is anaerobic threshold the same as lactate threshold?

For practical training they are used interchangeably and land at nearly the same intensity. The difference is historical: anaerobic threshold came from breathing-gas measurements, while lactate threshold comes from blood sampling. Most physiologists now prefer lactate threshold because muscles never actually stop using oxygen at this point.

What percentage of VO2 max is the anaerobic threshold?

It depends on training status. In untrained people the anaerobic threshold sits around 50 to 60 percent of VO2 max, while well-trained endurance athletes can push it to 80 to 90 percent. A higher percentage means you can use more of your aerobic engine before fatigue sets in.

What heart rate is my anaerobic threshold?

For most people the anaerobic threshold falls near 80 to 90 percent of maximum heart rate, and about 85 percent is a common estimate. The most reliable way to find yours is a 30-minute time trial: your average heart rate over the last 20 minutes closely matches threshold heart rate.

How do you increase your anaerobic threshold?

Combine sustained threshold work with a large easy aerobic base. Run or ride tempo efforts of 20 to 40 minutes, or cruise intervals at threshold pace, once or twice a week, and keep most other sessions easy. Over weeks this shifts the lactate curve so you hold a faster pace at the same effort.

What is a good anaerobic threshold?

A good threshold is a high fraction of your VO2 max, not just a fast pace. Recreational athletes often sit near 60 to 75 percent of VO2 max, while elite endurance athletes reach 85 to 90 percent. Because it predicts endurance performance well, raising your own threshold matters more than hitting any fixed number.

How is anaerobic threshold measured?

In a lab it is measured two ways: a blood lactate step test, where lactate is sampled at rising intensities and read near 4 mmol/L, or a gas exchange test that tracks the point where breathing rises steeply. Outside a lab, a maximal 30-minute time trial gives a solid field estimate.

What is the difference between aerobic and anaerobic threshold?

The aerobic threshold (LT1) is the lower point where lactate first rises above baseline, around 2 mmol/L, marking easy sustainable effort. The anaerobic threshold (LT2) is higher, around 4 mmol/L, marking the top of sustainable hard effort. Together they bracket the aerobic-anaerobic transition zone.

Is a higher anaerobic threshold better?

Yes, for endurance. A higher threshold lets you hold a faster pace or higher power before lactate accumulates and fatigue forces you to slow. It also speeds recovery between hard efforts in team sports. This is why threshold is often a better predictor of race performance than VO2 max alone.

Why do scientists criticise the term anaerobic threshold?

Because the name implies muscles run out of oxygen and switch to oxygen-free metabolism, which does not happen. Oxygen is used continuously, and lactate is produced aerobically at every intensity. Researchers such as George Brooks argue the label is physiologically invalid, so lactate threshold is the preferred, more accurate term.

References

1. Brooks GA. The 'Anaerobic Threshold' Concept Is Not Valid in Physiology and Medicine. Med Sci Sports Exerc, 2021. PMC9124087
2. Faude O, Kindermann W, Meyer T. Lactate threshold concepts: how valid are they? Sports Medicine, 2009. PubMed 19453206
3. Ghosh AK. Anaerobic threshold: its concept and role in endurance sport. Malays J Med Sci, 2004. PMC3438148
4. Cerezuela-Espejo V, et al. The Relationship Between Lactate and Ventilatory Thresholds in Runners: Validity and Reliability. Front Physiol, 2018. PMC6167480
5. Meyer T, et al. Is determination of exercise intensities as percentages of VO2max or HRmax adequate? Med Sci Sports Exerc, 1999. PubMed 10487378
6. Lactate threshold. Wikipedia