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

Knowing your thresholds is a useful way to quantify effort and distribute your training load, but understanding what they mean and how to use them is vital to realizing performance improvement. In a way, the term “threshold” can be a bit confusing, as it is commonly used to represent different things. This guide breaks down what each threshold (VT1, VT2, and VO₂max) actually represents how to find them, what they feel like, what physiologically happens at each one, and how to train each one for the largest performance gains.

Arguably, the most useful way to use thresholds is to identify the body’s need for different fuel sources. The human body generally uses a mixture of fatty acids and carbohydrates to generate fuel for the working muscles (ATP**). However, this mixture is not always the same. In general, more fat is used for fuel at lower efforts, while high intensity workouts require more carbohydrates (1*). The reason for this is that the breakdown of fatty acids is a slower and more efficient process resulting in less waste, i.e. exhaled CO2 (4*). 

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	3 / 10	Comfortable conversation	Mostly fat, increasing carbohydrate
VT2 (anaerobic threshold)	Complete switch to carbohydrate; 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 much 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)

When starting out at a low effort, whether running or cycling, one utilizing a high amount of fat to produce the energy necessary. At some point the fat oxidation starts to drop and carbohydrates pick up the slack resulting in excess CO2 and an increase in minute ventilation to exhale that CO2. At this point, it’s safe to assume that we have passed our first ventilatory threshold, VT1.

This effort level varies by person. Some can easily maintain a jog, or even a run, while others need only walk briskly to reach this point. When training close to your VT1, the body is receiving a very high stimulus for fat metabolism. Training at this effort level will help you become more efficient in using oxygen and burning fat. Formation of slow twitch (type I) muscle fibers is increased, and mitochondrial density and function is positively affected. 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*).

The Second Ventilatory Threshold (VT2) 

The key to building a strong aerobic foundation is allowing your mitochondria to rely on fat as a fuel source. When your effort increases beyond your First Threshold (VT1), carbohydrates become an increasingly prominent source of fuel. This is due to an increase in Type II muscle fiber recruitment, also known as fast twitch fibers. This results in your muscles down-regulating the use of fat as a fuel source. This happens because the mitochondria within the muscle cells need a more accessible and more easily digested fuel source. A byproduct of increased carbohydrate consumption is increased CO2 production, which triggers faster and deeper breathing.

This point of the body’s intensity and effort is also associated with increased blood lactate content. Working muscles start shuttling lactate to other tissues when they have reached their capacity to metabolize their own lactate production (6*). If the effort is increased beyond this point, there will come a time when the athlete can no longer sustain any fatty acid oxidation and the ATP needed for muscle contraction is only fueled by the breakdown of carbohydrates. This effort level is closely correlated with what has been termed the “anaerobic threshold”, or second ventilatory threshold, VT2 (7*).

At the second ventilatory threshold, the breathing rate starts to increase significantly. It is important to note that this point does not represent what has become known as the “maximum lactate steady state” (MLSS), but rather is an indication of the complete switch to carbohydrates as a fuel source (8* 9*). In a study published in Oxidative Medicine and Cellular Longevity in 2019, it was indicated that at efforts close to VT2, no specific benefit for either mitochondrial respiration or their volume in the muscle was obtained (11*). Therefore, training at or close to VT2 can provide temporary benefits for lactate tolerance in an athlete when a race is approaching, but might otherwise only contribute to extra fatigue. The “temporary” part of the previous sentence is the key here, as the lactate tolerance changes will eventually be overshadowed by the decrease in mitochondrial density and respiration due to not enough training at low or high intensities.

VO₂max 

When continuing 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). The most efficient way to increase VO₂max for the vast majority of people is to lose weight, although increases in the uptake of oxygen itself (ml/min) can also be seen when exercising regularly (10*). At your body’s VO₂max, your breathing frequency can often go up to 50-60 times per minute and lead you to start to hyperventilate, which causes increased fatigue.

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 3 / 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 9 / 10). Hyperventilating. Effort can only be sustained in short bursts.

Is VT2 the Same as the Anaerobic Threshold or the Lactate Threshold?

Anaerobic threshold (AT), 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	Practical equivalence
VT2 (second ventilatory threshold)	The disproportionate rise in ventilation as CO₂ removal accelerates	Breathing data:  minute ventilation, VE/VO₂, VE/VCO₂ during a ramp test	The point where you can only speak a couple of words at a time
AT (anaerobic threshold)	The intensity at which lactate production exceeds clearance	Conceptual marker; historically inferred from lactate or breathing	Functionally the same effort as VT2
LT / LT2 (lactate threshold)	A specific blood-lactate value (commonly ~4 mmol/L, but it varies)	Finger-prick lactate sampling during a step test	Sits very close to VT2 in most athletes; the exact numeric anchor depends on the lab’s protocol
MLSS (maximum lactate steady state)	The highest intensity where blood lactate stabilizes rather than rising	Multiple ~30-minute constant-load efforts with lactate sampling	Sits below VT2 in most studies — VT2 is not MLSS

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. MLSS is the one term that meaningfully diverges and should not be conflated with VT2.

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.

How to Train Each Threshold 

How to Improve VT1 

VT1 responds to volume at low intensity. Long, easy efforts at or just below VT1 deliver the largest stimulus for fat metabolism, mitochondrial density, and type-I muscle fiber development (5*). This is the same domain commonly called Zone 2. Over time, repeated exposure raises VT1, allowing the athlete to perform more work at lower perceived effort.

Practically, this means most weekly training volume should sit at or below VT1. Runs and rides where conversation is easy, breathing is controlled, and the effort feels sustainable for hours.

How to Improve VT2 

VT2 responds to sustained efforts at or just below threshold, doing the workouts traditionally called tempo runs, threshold workouts, or tempo intervals. At this intensity, the athlete is putting a significant amount of stress on the system without going over the lactate tipping point.

The performance translation is concrete. At the start of a season a triathlete might hold 20 mph on the bike and run a 9:00 mile. After a season of well-targeted threshold work, that same athlete can be cycling at 23 mph and running 8:30 per mile but at the same internal effort. Because the threshold itself is now higher, the athlete cycles and runs faster while burning fuel more efficiently across the whole race (19*).

A second VT2-style approach is high-intensity interval training (HIIT): short, hard intervals above threshold alternated with active recovery. HIIT pushes the same adaptations from a different angle.

How to Train VO₂max

Training in short efforts at or above VO₂max can provide improvements in mitochondrial respiration, improving the muscles’ ability to consume oxygen and use fuel at high loads (11*). Typical training efforts last from half a minute up to two minutes. At this intensity, the body is only burning carbohydrates for fuel and there is no fatty acid oxidation. Lactate build-up is high, and the body can only sustain the effort for a short period of time. Because the effort load on the system is so high, there’s usually a longer recovery time both in the short term (within a session) and the long term (within the week). For that reason, VO₂max sessions should only be used 1–2 times per week, balanced by longer and easier sessions at lower intensities closer to VT1.

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 3/10.

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 most accurate methods are a metabolic test (breath-by-breath gas analysis on a ramp protocol) or a lactate step test. Both can be done in a performance lab. In the field, ventilation can be measured directly with a wearable like the Tymewear VitalPro chest strap, which uses breathing data to identify VT1 and VT2 the same way a metabolic cart does.

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.

Is the lactate threshold (LT) the same as VT2?

Very close, but not exactly identical. LT (often defined as the intensity at which blood lactate exceeds 4 mmol/L) sits very near VT2 in most athletes. The exact relationship varies by individual and by lab protocol.

Is VT2 the same as MLSS?

No. Maximum lactate steady state (MLSS) is the highest intensity at which blood lactate stabilizes rather than rising. MLSS typically sits below VT2.

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.

**ATP (Adenosine triphosphate) is a molecule produced by our cells when metabolizing either carbohydrates, fatty acids 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