Ventilatory Thresholds (VT1 & VT2) — The Complete Guide

Ventilatory thresholds (VT1 and VT2) have become central indicators for measuring aerobic performance, structuring training zones, calibrating intensity and tracking the progress of athletes.

Unlike traditional methods based on heart rate or power, ventilatory thresholds directly describe the body's internal physiological response to exertion.

This comprehensive guide explains:

• What are VT1 and VT2?

• how they measure themselves,

• their link with the energy sectors,

• their role in the training areas,

• their advantages compared to lactate tests,

• how to use them in running, trail running, cycling or triathlon,

• how ZoneX allows us to measure them in real-world conditions.

1. What are ventilatory thresholds?

VT1 – The first ventilatory threshold

This is the moment when breathing accelerates slightly to compensate for the increase in CO₂ produced by the increased use of carbohydrates.

In concrete terms:

• The ventilation begins to rise in a non-linear fashion.

• Breathing remains fluid but deeper.

• The conversation becomes slightly more difficult.

👉 VT1 marks the end of easy endurance and the beginning of sustained intensity.

VT2 – The second ventilatory threshold

This is a ventilatory breakdown: ventilation explodes in an attempt to compensate for muscle acidosis.

Physiologically:

• a sharp and disproportionate increase in respiration,

• maximum CO₂ removal

• major shift in anaerobic metabolism.

👉 VT2 is the upper physiological limit before acidosis limits effort.

2. The link between ventilatory thresholds and energy pathways

Sector	associated ventilatory zone	Substrates
Low aerobic capacity	Under VT1	Lipids
Sustained aerobic exercise	Around VT1	Lipids + carbohydrates
High-intensity aerobic exercise	Between VT1 and VT2	Carbohydrates
Anaerobic	Above VT2	Carbohydrates + acidosis

Ventilatory thresholds are therefore a direct reflection of energy metabolism .

3. How to measure VT1 and VT2?

Classic method: cardiopulmonary testing (CPET)

Produced in a laboratory using:

• analysis of exhaled gases,

• precise measurement of CO₂

• Wasserman algorithms.

Very precise… but expensive and not reproducible in the field.

Lactate method: indirect and invasive

• requires blood tests,

• very sensitive to nutrition, stress, hydration,

• can give inconsistent results.

👉 Useful in the lab, but difficult to repeat every week.

Modern method: on-board ventilatory analysis (ZoneX)

ZoneX detects respiratory transitions through:

• respiratory rate

• ventilatory variability,

• the compensation indices,

• ventilatory drift.

Benefits :

• measurement under real-world conditions (climbing, running, cycling)

• automatically detects VT1 & VT2,

• repeatable at each session.

👉 This is the most practical method for daily training.

Measure your thresholds with ZoneX

4. Training zones based on VT1 & VT2

Here are the universal correspondences between zones and thresholds:

• Zone 1: below VT1 → basic endurance

• Zone 2: around VT1 → mitochondrial development

• Zone 3: between VT1 and VT2 → sustained tempo/intensity

• Zone 4: near VT2 → threshold capacity

• Zone 5: above VT2 → high intensity / VO₂max

Why is this superior to zones based on heart rate or power?

• heart rate drifts

• Power depends on the terrain.

• Respiration reflects metabolism in real time .

5. VT1 & VT2 depending on the sport

Cycling

• VT1 → long endurance pacing

• VT2 → mountain pass management, restarts, time trial

Running

• VT1 → aerobic endurance zone

• VT2 → 10km/half-marathon pace and uphill pacing

Triathlon

• VT1 → swimming + long-distance cycling

• VT2 → regulation of transitions

Trail

• VT1 → long climb

• VT2 → technical climb and hill holding threshold

6. Common errors regarding ventilatory thresholds

• Use only FC to define zones

• Base on %FTP or %VO₂max

• Neglecting the impact of fatigue on VT1

• Confusing VT2 and subjective “threshold pace”

• Do not measure regularly

👉 The thresholds change every 2–4 weeks.

7. How to use ZoneX to leverage your thresholds

ZoneX allows you to:

• automatically detect VT1 and VT2,

• display your zones in real time,

• adapt your training to your fatigue level that day.

• to avoid ventilatory drift,

• track your respiratory progress week by week.

It's a portable breathing test that transforms your breathing into a training tool.

Learn more about ZoneX

8. Why ventilatory thresholds predict endurance better than VO₂max

Unlike VO₂max (which is not very discriminating), VT1 and VT2:

• better predict actual performance

• reflect training adaptations,

• evolve with the load.

• differentiate athletes with the same VO₂max.

Go further on the PAIRFS blog

• Understanding ventilatory thresholds: the foundation for optimizing your training

• How to track progress using ventilatory thresholds?

• Respiratory analysis: the most reliable method to determine your training zones

• Field test vs laboratory test: what are the differences for respiratory measurement?

• Can a lactate test be replaced by a ventilatory test? Advantages and limitations

  
  

Scientific references

1. Wasserman K. et al. (2011). Principles of Exercise Testing and Interpretation.

2. Pallarés JG et al., 2016. Validity of Ventilatory Thresholds. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0163389

3. Anselmi F. et al., 2021. Importance of ventilatory thresholds. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8456830/

4. Poole DC, Jones AM, 2021. Oxygen Uptake Kinetics. https://doi.org/10.1002/cphy.c200006

5. Cerezuela-Espejo V. et al., 2018. Lactate vs ventilatory thresholds. https://www.frontiersin.org/articles/10.3389/fphys.2018.01320/full

6. Weston S., Gabbett T., 2001. Reproducibility of VT2. https://pubmed.ncbi.nlm.nih.gov/11702922/

7. Meyer T. et al., 2005. Criteria for Exercise Intensity Prescription. https://pubmed.ncbi.nlm.nih.gov/15907278/