Guide · Thresholds

Ventilatory thresholds VT1 and VT2, explained

VT1 and VT2 are where your breathing changes pace in a ramp test. How they're found, how they relate to lactate, and how they set training zones.

Last reviewed 2026-10-16 · By the VenTracer team, Rapid Circuitry · Sources

The short answer

Two breaks in your breathing

Ventilatory thresholds are the two points in a ramp test where your breathing changes pace. At the first, VT1, breathing starts rising faster than oxygen use. At the second, VT2, breathing outpaces even the carbon dioxide you produce. Together they divide exercise into three intensity zones, and they are found from breath gas measurements, not from heart rate.^1,2

Definitions

What happens at VT1 and VT2

As effort rises, your muscles produce more lactate and hydrogen ions. Your blood buffers the acid with bicarbonate, and that releases extra carbon dioxide. Your breathing responds to it in two steps.¹

VT1: the first threshold

VT1 is where buffering starts adding extra CO₂. Carbon dioxide output, and the breathing that clears it, now climb faster than oxygen uptake. Beaver, Wasserman and Whipp showed this point closely predicted the lactate and bicarbonate thresholds.¹

VT2: the respiratory compensation point

Higher up, buffering can't keep pace. Your body starts breathing off more CO₂ to limit the rise in acidity. Ventilation now climbs faster than CO₂ output, and the CO₂ at the end of each breath starts to fall. This is VT2, also called the respiratory compensation point (RCP).² In the original V-slope study, it always sat well above VT1.¹

A note on names

A review of the terms noted that "anaerobic threshold" has been used for both the first and the second threshold, "bearing a great potential of confusion".²

Threshold	Other names you'll see	Breathing signature
VT1	Aerobic threshold, gas exchange threshold, first lactate threshold (LT1)	VE/VO₂ rises while VE/VCO₂ stays flat
VT2	Respiratory compensation point, second lactate threshold (LT2), sometimes "anaerobic threshold"	VE/VCO₂ rises and end-tidal CO₂ falls

Detection

How thresholds are found

Both thresholds come from a ramp test with breath-by-breath gas analysis. Physiologists use two main methods, and good practice is to check one against the other.

The V-slope method

Plot CO₂ output against O₂ uptake. Early in the test the points form a straight line. At VT1 the line steepens, because extra CO₂ from buffering joins the CO₂ from metabolism. Beaver and colleagues introduced this method in 1986 because it doesn't depend on a regular breathing pattern. For VT2 they used a separate plot of ventilation against CO₂ output.¹

Ventilatory equivalents

A ventilatory equivalent is the air you breathe per litre of gas exchanged: VE/VO₂ for oxygen and VE/VCO₂ for carbon dioxide. VT1 is where VE/VO₂ starts to rise without a rise in VE/VCO₂. VT2 is where VE/VCO₂ starts to rise too, and end-tidal CO₂ drops.²

How repeatable are they?

In 14 trained cyclists tested twice, threshold workloads from ventilatory equivalents repeated with a coefficient of variation of 1.6% to 3.5%. The V-slope and RER-equals-1 methods were less repeatable in that study (5.0% to 6.4%).³ It makes sense to confirm one method with the other.

Lactate

How ventilatory and lactate thresholds relate

Lactate thresholds come from finger or earlobe blood samples. Ventilatory thresholds come from breath. They track the same underlying shift, but they are not identical numbers.

In the cycling study above, the workload at the first lactate threshold matched VT1. A lactate marker 2.0 mmol/L above it matched VT2.³
A review of lactate methods found 25 different lactate threshold concepts in the literature. So "your lactate threshold" depends on which one was used.⁴
In 12 men, the respiratory compensation point occurred at the same oxygen uptake as critical power and maximal lactate steady state, the classic upper limit of sustainable effort. But the power at RCP on the ramp was higher than critical power or maximal lactate steady state.⁵

The practical point: breath gives both thresholds from one test, with no blood samples. Treat the power or pace shown at VT2 on a ramp as an upper bound for steady efforts.

Training zones

The three‑zone model

VT1 and VT2 split intensity into three zones. Seiler and Kjerland used exactly these boundaries to describe how elite endurance athletes train.⁶

Zone	Boundary	Effort	Typical use
Zone 1	Below VT1	Easy	Long, high-volume aerobic work
Zone 2	VT1 to VT2	Moderate to hard	Tempo and threshold sessions
Zone 3	Above VT2	Very hard	Intervals near VO₂max

In their junior cross-country skiers, about 75% of endurance sessions fell in zone 1, 8% in zone 2 and 17% in zone 3, by heart rate.⁶ Seiler's later review described a similar pattern across elite endurance sports: about 80% of sessions at low intensity.⁷ Other zone systems split intensity differently, so a "zone 2" elsewhere may not match zone 2 here.

Heart-rate formulas

Why 220 minus age falls short

Most watch zones start from an estimated maximum heart rate, then take fixed percentages of it. Both steps add error.

The formula is a group average. A meta-analysis of 18,712 people produced a better equation, 208 − 0.7 × age, and found 220 − age underestimates maximum heart rate in older adults.⁸
Individuals scatter widely. In 3,320 healthy adults in Norway's HUNT study, age-based prediction had a standard error of 10.8 beats per minute.⁹ If your true maximum is 11 beats off the formula, every zone built on it is off too.
Fixed percentages don't match thresholds. In 100 women and men, prescriptions based on fixed percentages of maximum heart rate, VO₂max or peak power "conform poorly" to each person's intensity domains.¹⁰
The same percentage feels different. At 60% of VO₂max, blood lactate in 21 healthy men ranged from 0.7 to 5.6 mmol/L.¹¹

Measured thresholds avoid these problems. Once you know the heart rate, power and pace at your own VT1 and VT2, you can train by those numbers. For the bigger picture of the test itself, see VO₂max testing: how it's measured, and what the number means.

FAQ

Common questions

QuestionIs VT1 the same as the aerobic threshold or LT1?

They describe the same transition, measured in different ways. VT1 is found from breathing and gas exchange. LT1 is found from blood lactate. In a study of trained cyclists, the workload at the first lactate threshold matched the workload at VT1.³ The names are used loosely, so check which method a report used.

QuestionIs VT2 the same as the lactate threshold?

VT2, also called the respiratory compensation point, sits near the top of the range you can sustain, close to maximal lactate steady state and critical power.⁵ In one cycling study, the workload at VT2 matched a lactate marker 2 mmol/L above the first lactate threshold.³ The term "anaerobic threshold" has been used for both thresholds, which causes confusion.²

QuestionCan I find my thresholds from heart rate alone?

Not reliably. Formulas such as 220 minus age predict maximum heart rate with a standard error of about 11 beats per minute, and fixed percentages of maximum fit individual thresholds poorly.^9,10 Once a gas-exchange test has found your thresholds, you can note your heart rate at each one and train by those numbers.

QuestionWhy are my thresholds different on the bike and the run?

Mode matters. In a classic comparison of the same people, the anaerobic threshold was about 13% higher on the treadmill than on the cycle ergometer, and VO₂max about 6% higher.¹² Test in the sport you train for, and don't copy zones from one to the other.

QuestionWhy does my VT2 power feel too hard to hold?

The power shown at VT2 on a ramp test can be higher than the power you can hold steadily. One study found the respiratory compensation point occurred at the same oxygen uptake as critical power and maximal lactate steady state, but at a higher power on the ramp.⁵ Treat ramp power at VT2 as an upper bound for long, steady efforts.

Where VenTracer fits

Thresholds from every breath

VenTracer is a wireless breath analyzer, in development, designed to find VT1 and VT2 the way a lab does: breath flow, oxygen and carbon dioxide on every breath, with the V-slope method cross-checked against ventilatory equivalents. It hasn't been validated yet. We will compare it with a laboratory metabolic cart on the same athletes and publish the results before making any accuracy claim. See the planned methods, or join the validation work.

Sources

References

Beaver WL, Wasserman K, Whipp BJ. A new method for detecting anaerobic threshold by gas exchange. J Appl Physiol. 1986;60(6):2020–2027. PubMed 3087938
Binder RK, Wonisch M, Corra U, et al. Methodological approach to the first and second lactate threshold in incremental cardiopulmonary exercise testing. Eur J Cardiovasc Prev Rehabil. 2008;15(6):726–734. PubMed 19050438
Pallarés JG, Morán-Navarro R, Ortega JF, et al. Validity and reliability of ventilatory and blood lactate thresholds in well-trained cyclists. PLoS One. 2016;11(9):e0163389. PMC5033582
Faude O, Kindermann W, Meyer T. Lactate threshold concepts: how valid are they? Sports Med. 2009;39(6):469–490. PubMed 19453206
Keir DA, Fontana FY, Robertson TC, et al. Exercise intensity thresholds: identifying the boundaries of sustainable performance. Med Sci Sports Exerc. 2015;47(9):1932–1940. PubMed 25606817
Seiler KS, Kjerland GØ. Quantifying training intensity distribution in elite endurance athletes: is there evidence for an "optimal" distribution? Scand J Med Sci Sports. 2006;16(1):49–56. PubMed 16430681
Seiler S. What is best practice for training intensity and duration distribution in endurance athletes? Int J Sports Physiol Perform. 2010;5(3):276–291. PubMed 20861519
Tanaka H, Monahan KD, Seals DR. Age-predicted maximal heart rate revisited. J Am Coll Cardiol. 2001;37(1):153–156. PubMed 11153730
Nes BM, Janszky I, Wisløff U, et al. Age-predicted maximal heart rate in healthy subjects: the HUNT fitness study. Scand J Med Sci Sports. 2013;23(6):697–704. PubMed 22376273
Iannetta D, Inglis EC, Mattu AT, et al. A critical evaluation of current methods for exercise prescription in women and men. Med Sci Sports Exerc. 2020;52(2):466–473. PubMed 31479001
Scharhag-Rosenberger F, Meyer T, Gässler N, et al. Exercise at given percentages of VO₂max: heterogeneous metabolic responses between individuals. J Sci Med Sport. 2010;13(1):74–79. PubMed 19230766
Buchfuhrer MJ, Hansen JE, Robinson TE, et al. Optimizing the exercise protocol for cardiopulmonary assessment. J Appl Physiol. 1983;55(5):1558–1564. PubMed 6643191

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