VT1, VT2, and VO₂max: The Complete Guide to Ventilatory Thresholds

Your thresholds, whether measured by ventilation or lactate, fundamentally define your training zones. But the term itself can be confusing, since "threshold" gets used to mean many different things. This guide breaks down what thresholds (VT1, VT2, and VO₂max) actually represent, how to find them, what they feel like during training, what physiologically happens at each one, and how to train each one for the largest performance gains.

What Are VT1, VT2, and VO₂max? 

Before reaching VO₂max, every athlete passes through two metabolic transitions — the first ventilatory threshold (VT1) and the second ventilatory threshold (VT2). Each marks a shift in how energy is produced, how sustainable an effort is, and how the body breathes (12*).

Threshold	What it represents	Approximate RPE	Talk test	Primary fuel
VT1 (aerobic threshold)	First major shift from fat to carbohydrate; ventilation starts to rise faster than oxygen demand	4 / 10	Manageable conversation	Max fat reached, stable carbohydrate
VT2 (anaerobic threshold)	Transition to carbohydrates; CO₂ production drives a sharp ventilation increase	7 / 10	Only a couple of words at a time	Carbohydrate dominant
VO₂max	Ceiling of the aerobic system and the highest rate at which the body can transport and use oxygen	9 / 10	Hyperventilating, no speech	Carbohydrate only

A less conditioned athlete will reach VT1, VT2, and VO₂max at lower intensities than a fitter athlete. A deconditioned athlete may arrive at VT1 at a brisk walk, while a conditioned athlete reaches VT1 at a moderate run.

The First Ventilatory Threshold (VT1) - aka "Zone 2" training

VT1 is the ceiling of the popular "Zone 2" training. It's not just hype. VT1 wins races. It's also the foundation on which the rest of your fitness, and your long-term health, is built. Seiler et al. (20*) found: "Despite similar RPE, blood lactate and carbohydrate oxidation rates, the better performance by the Well Trained group was explained by their nearly threefold higher rates of fat oxidation at high intensity." The more fat you burn, the fitter you are, and the better you perform. VT1 marks the transition from fat to carbohydrate as the muscle's dominant fuel source. Training at and below VT1 drives the adaptations that push VT1 to higher intensities.

Your current VT1 informs how you should train to improve endurance. If VT1 is low, chasing VO₂max will yield diminishing returns. If VT1 is high, VO₂max becomes low-hanging fruit. How these two ebb and flow across a training cycle determines the intensity distribution that fits your current fitness level.

By training at and below VT1 the muscles adapt to using more fat by increasing mitochondrial density. This adaptation sets the foundation for increasing VO2max. One can see the evidence of this fat metabolism stimulus when looking at elite endurance athletes, as they have a significantly higher number of mitochondria and fatty acid oxidation compared to the normal population (5*).

VT1 intensity is moderate: not particularly hard, but not easy either. After the workout, your muscles feel worked but refreshed, like you could have done more. You'll feel it in your legs the next day, but not enough to compromise your next session. This is what makes VT1 training so impactful: recoverability and adaptation signal are both high, which means you can safely do lots of volume here with minimal risk of overtraining.

How to Improve VT1 

VT1 workouts take two forms: steady state at an intensity somewhat below VT1, and 10-30 minute intervals that go up to VT1. The duration of the steady state, along with the frequency and duration of the intervals, depends on your overall fitness and where you are in your training progression.

The Second Ventilatory Threshold (VT2) 

When your effort increases beyond your First Threshold (VT1), carbohydrates become an increasingly prominent fuel source. This is due to greater recruitment of Type II muscle fibers (also known as fast-twitch fibers), which causes your muscles to down-regulate fat oxidation. The mitochondria in your muscle cells need a more accessible and faster-burning fuel as relative intensity ramps up. Burning more carbohydrate produces more lactate and CO₂ as byproducts. Rising CO₂ triggers an increase in ventilation to breathe out the excess. This transition has been termed the "anaerobic threshold", or second ventilatory threshold, VT2 (7*).

VT2 stands on the shoulders of the adaptations from VT1. The higher your mitochondrial density, the better your muscles are at consuming the lactate produced at this intensity (6*). When your muscles can use lactate as fuel, less carbohydrate gets burned overall, which means less CO₂, which means VT2 happens at higher intensities. Eventually, the effort climbs beyond your ability to consume lactate and ventilation increases significantly as a result of the excessive CO2 production.

There is a strong correlation between speed at VT2 and performance. In well trained athletes it is approximately the 1 hour race pace. In the now famous "Norwegian Method" VT2 or LT2 is the anchor for the interval sessions that the method has made famous (21*). It's important to note that the "Norwegian Method" consists of very high low intensity volume with key tightly controlled high intensity sessions. 

How to Improve VT2 

VO₂max 

VO2max has the best publicist in human physiology. Ironically, it's the least useful from a training and racing standpoint when compared to VT1 and VT2. We arrive at VO2max as we continue to increase the effort level above VT2, you will soon reach your VO₂max. This point, as indicated by its name, is the absolute maximal oxygen uptake the body is capable of as measured in milliliters per minute per kilogram (ml/min/kg). At your body’s VO₂max, your ventilation will be at its highest, breathing frequency can often go up to 50-60 times per minute. RPE will be above 8/10.

How to Train VO₂max

The most efficient way to increase VO₂max is to simply lose weight. To increase the uptake of oxygen itself (ml/min) is achieved through a mixture of VT1 and VT2 training which creates the mitochondrial density and durability that enables more oxygen to be consumed. As Seiler et al showed in the VT2 section, VO2 improved the most with 4x8 minutes at an intensity between VT2 and VO2max as compared to shorter intervals like 4x4 minutes at VO2max. 

How Each Threshold Feels: RPE Anchors 

The cleanest field-side way to know which threshold you’re sitting at is the talk test, anchored to the Rate of Perceived Exertion (RPE) scale.

• At VT1 (RPE 4 / 10). Breathing is elevated but comfortable. Lactate is being produced, but the body clears it as quickly as it’s being made (12*).
• Between VT1 and VT2 (RPE 4–6 / 10). Breathing rises noticeably. The fuel mix is shifting from fat-dominant toward carbohydrate-dominant.
• At VT2 (RPE 7 / 10). Breathing and lactate rise exponentially. VT2 is also referred to as the anaerobic threshold (AT) (12*).
• At VO₂max (RPE 8+ / 10). Max Ventilation. Effort can only be sustained for several minutes.

Are Ventilatory Thresholds and Lactate Thresholds the Same?

Lactate threshold (LT), and the second ventilatory threshold (VT2) are often used interchangeably and for most practical training purposes they refer to the same physiological transition. They’re measured slightly differently, however, and they sit on slightly different physiological signals.

Term	What it measures	How it’s detected
VT1/VT2 (first and second ventilatory threshold)	The increase in ventilation as CO₂  production increases and its removal accelerates.	Breathing data:  minute ventilation, VE/VO₂, VE/VCO₂ during a ramp test
LT1 / LT2 (first and second lactate threshold)	A specific blood-lactate value (commonly ~2 and 4 mmol/L, but it varies)	Finger-prick lactate sampling during a step test

The takeaway: when an athlete or coach says “anaerobic threshold,” they almost always mean the same physiological transition as VT2. The labels differ because the historical research traditions used different measurement signals: gas exchange vs blood lactate. The underlying event in the body is the same.

Why Accurate, Individual Thresholds Matter More Than Heart Rate Zones 

Polar’s Sport Tester PE 2000 came out in 1982, and since then heart rate has been the standard measurement of intensity for endurance exercise (13*). It’s been a useful proxy, but as a way to prescribe training intensity it has a serious problem: an individual’s heart rate response is not only governed by how hard they’re exercising. Genetics, stress, heat, caffeine, and how rested someone is all change the heart-rate response from day to day and from person to person (14*)(15*). Together these confounders add up to roughly a 29% error margin when using heart rate or heart-rate-reserve formulas alone to estimate training intensity (16*).

That error margin shows up clearly in the training-response data. In a 12-week randomized controlled trial, 60% of participants showed no improvement in VO₂max when they followed a program prescribed from heart rate reserve. In the same study, 100% of participants improved when their training was prescribed from their individual ventilatory thresholds (17*). For trained athletes the picture is even more pointed: a separate study found that, to keep improving fitness, it was not sufficient to set zones as percentages of max heart rate or VO₂max, only their unique anaerobic threshold worked (18*).

The reason is that thresholds are personal in a way that heart-rate percentages are not. Two athletes can share the same HRmax or VO₂max and still have very different VT1 and VT2 efforts. It’s like comparing the gears in two different cars: some engines reach 12,000 rpm before they need to shift, while others top out at 5,000. Having “larger gears” (high VT1) is an indication of strong metabolic ability and better overall endurance. When each individual’s unique spectrum is known, it can be trained and improved. That is how an athlete goes faster, for longer.

Distributing Training Across Thresholds 

The thresholds give you the intensities; the next question is how much time to spend at each one. The research consensus, most strongly from Stöggl & Sperlich’s 9-week study on polarised vs threshold vs HIIT vs HVT training, is that the most effective distribution for endurance athletes is roughly 80% of training below VT1 and ~20% above VT2, with very little time spent in the middle. The middle zone (between VT1 and VT2) feels productive but, as the 2019 Oxidative Medicine and Cellular Longevity finding above shows, returns relatively little adaptation per unit of fatigue.

The best plan, in other words, is built directly from your individual VT1 and VT2; not from a percentage of HRmax.

Frequently Asked Questions 

What is VT1?

VT1 (the first ventilatory threshold, sometimes called the aerobic threshold) is the intensity at which fat oxidation begins to give way to carbohydrate use. Ventilation starts to rise faster than oxygen demand, breathing becomes noticeably elevated, and conversation gets harder to hold in full sentences. VT1 sits at roughly RPE 4/10.

What is VT2?

VT2 (the second ventilatory threshold, or anaerobic threshold) is the intensity at which the body switches almost entirely to carbohydrate metabolism. CO₂ production accelerates, ventilation rises sharply, and the athlete can only speak a couple of words at a time. VT2 sits at roughly RPE 7/10.

What is VO₂max?

VO₂max is the maximal rate at which the body can take in, transport, and use oxygen during exercise, measured in milliliters of oxygen per kilogram of body weight per minute (ml/min/kg). It defines the ceiling of the aerobic system.

How do I find my VT1 and VT2?

The Tymewear app guides you through a 20-30 minute protocol from low intensity to max effort. The VitalPro measures your Minute Ventilation throughout and the inflection points at VT1 and VT2 are identified.

Is VT2 the same as the anaerobic threshold?

For most practical training purposes, yes. The terms historically come from different measurement traditions (VT2 from gas exchange, AT/LT from lactate sampling) but they refer to the same underlying transition.

 

Lactate threshold (LT), and the second ventilatory threshold (VT2) are often used interchangeably and for most practical training purposes they refer to the same physiological transition. They’re measured slightly differently, however, and they sit on slightly different physiological signals.

 

Can I improve my thresholds?

Yes! That is the point of structured endurance training. VT1 and VT2 both move to higher intensities with consistent training. The fastest gains come from targeting each threshold with the right type of work: long, easy work below VT1 to raise VT1, and threshold/HIIT work to raise VT2, together they raise VO2max.

**ATP (Adenosine triphosphate) is a molecule produced by our cells when metabolizing either carbohydrates, fat or, to a lesser extent, proteins. ATP is then used for muscle contraction and is therefore essential for all life.

References:

1. https://www.researchgate.net/profile/Asker_Jeukendrup/publication/9026407_Maximal_Fat_Oxidation_During_Exercise_in_Trained_Men/links/0fcfd50b07fb5af17b000000/Maximal-Fat-Oxidation-During-Exercise-in-Trained-Men.pdf
2. https://www.sciencedirect.com/science/article/abs/pii/0002914964900128
3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2786109/
4. https://www.ncbi.nlm.nih.gov/books/NBK531494/
5. https://onlinelibrary.wiley.com/doi/full/10.1111/sms.13298
6. https://pubmed.ncbi.nlm.nih.gov/28623613/
7. https://link.springer.com/article/10.1186/s40798-016-0060-1
8. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5143771/
9. https://journals.plos.org/plosone/article/file?type=printable&id=10.1371/journal.pone.0163389
10. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3774727/
11. https://www.hindawi.com/journals/omcl/2019/7058350/
12. https://pubmed.ncbi.nlm.nih.gov/8425510/ — VT1 and VT2 from breathing
13. https://books.google.is/books?id=ObUUAQAAMAAJ&q=isbn:9780963463302 — Polar Sport Tester PE 2000 (1982) historical reference
14. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2164943/ — Caffeine and heart rate response
15. https://www.ncbi.nlm.nih.gov/books/NBK236240/ — Heat stress and cardiovascular response
16. Myers, J. et al. (1999) — 29% error margin in heart-rate-derived training zones
17. https://bmcsportsscimedrehabil.biomedcentral.com/articles/10.1186/s13102-015-0011-z — Wolpern, Burgos, Janot & Dalleck (2015): 60% non-responders to HRR-prescribed training vs 100% responders to threshold-prescribed training
18. https://pubmed.ncbi.nlm.nih.gov/10487378/ — Trained athletes require individual anaerobic threshold, not %HRmax / %VO₂max
19. Soultanakis, H. N., Mandaloufas, M. F., & Platanou, T. I. (2012). Lactate threshold and performance adaptations to 4 weeks of training in untrained swimmers: Volume vs. intensity. Journal of Strength and Conditioning Research, 26(1), 131–137. https://doi.org/10.1519/JSC.0b013e31821eb7bd
20. https://www.researchgate.net/publication/283017321_Rethinking_the_role_of_fat_oxidation_substrate_utilisation_during_high-intensity_interval_training_in_well-trained_and_recreationally_trained_runners
21. https://pmc.ncbi.nlm.nih.gov/articles/PMC10000870/