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Understanding ventilatory thresholds: the basis for optimizing your training

Why talk about ventilatory thresholds?


Most athletes train using training zones. These zones are directly linked to your physiology and to the way your body produces energy: lipid-based aerobic metabolism, carbohydrate-based aerobic metabolism, or anaerobic metabolism. This physiology can be evaluated in two ways: by measuring blood lactate or by analyzing your breathing, which reflects in real time the balance between these energy pathways.


This is exactly what ventilatory thresholds reveal—two fundamental markers that indicate these metabolic transitions and allow you to define your true physiological training zones.


1. What is a ventilatory threshold?


During a progressive exercise test, your breathing does not follow a linear curve. At two specific moments, your body changes the way it produces energy: these are the ventilatory thresholds.


🔹 Ventilatory Threshold 1 (VT1)

It corresponds to the point where:

  • breathing begins to accelerate

  • the body increases carbohydrate use

  • fat oxidation becomes less dominant


This is the boundary between basic aerobic endurance and active endurance. Athletes often refer to this as Zone 2.


Below VT1:

💠 you are in pure aerobic endurance

💠 you burn mostly fats

💠 you can sustain the effort for a long time


🔹 Ventilatory Threshold 2 (VT2)

It corresponds to the point where:

  • ventilation increases very sharply

  • CO₂ production spikes

  • acidosis starts to appear

  • speaking becomes nearly impossible

This is the threshold close to critical power / FTP, or the classic “threshold zone.”


Above VT2:

🔥 the effort becomes very costly

🔥 the time you can sustain it drops dramatically

🔥 you shift into anaerobic intensities


Why are ventilatory thresholds more reliable than heart rate or field tests?


Training zones are often defined using maximum heart rate, HR percentages, or field tests like FTP (Coggan) or Valmaval/Vameval. These methods are simple, but they do not measure actual physiology.


🔹 Limitations of heart rate

Heart rate varies significantly with fatigue, heat, stress, hydration, or cardiac drift.Two identical sessions can produce very different HR values without any real change in metabolism.Most importantly, heart rate does not tell you whether you are using fats or carbohydrates.


🔹 Limitations of field tests

FTP, speed, or performance measure what you are capable of producing—not how your body produces that energy.Two athletes with the same FTP can have completely different physiological thresholds.


🔹 The advantage of ventilatory thresholds

Breathing directly reflects:

  • the substrates being used

  • CO₂ production

  • the acid–base balance

It shows precisely when the body switches metabolic pathways (VT1 / VT2).This is why ventilatory thresholds are the most accurate markers for defining truly individualized training zones.


3. How can you identify your ventilatory thresholds?


Until recently, you had to go to a laboratory for a VO₂ test with a mask, ergometer, and gas analyzers. It was precise, but limited to a small number of athletes.


Today, field-based solutions can analyze breathing without a complex protocol, directly during your training sessions.


This allows you to:

  • measure your thresholds regularly

  • track how they evolve

  • adjust your zones to match your physiology

  • build a much more effective training plan


4. How to use thresholds to train intelligently?


🔹 Below VT1 → Basic aerobic endurance


Objectives:

  • improve aerobic efficiency

  • develop oxygen transport

  • optimize fat oxidation


Use cases: long rides, active recovery.


🔹 Between VT1 and VT2 → Active endurance / tempo


Objectives:

  • accustom the body to using more carbohydrates

  • improve tolerance to mild lactate levels

  • prepare for sustained efforts


Use cases: tempo, rhythm sessions, pacing for hilly cyclosportives.


🔹 Above VT2 → Threshold / high intensity


Objectives:

  • increase maximal lactate-producing power

  • improve tolerance to acidosis

  • develop decisive high-intensity efforts


Use cases: intervals, short repeats, threshold blocks.



5. Why is this essential for progress?


Because you can easily be training in the wrong zone without realizing it.

Common situations:

  • thinking you’re in endurance… but actually above VT1

  • doing “threshold work” too low or too high

  • pacing a race incorrectly

  • burning through carbohydrate stores too early


With accurately identified ventilatory thresholds, you can:

  • train in the right zone

  • avoid overtraining

  • maximize progression

  • improve your efficiency at every effort level


👉 It is the most scientific and individualized way to structure a training plan.


6. How does ZoneX fit into this approach?


Precise measurement of ventilatory thresholds relies on respiratory analysis. ZoneX, developed by PAIRFS, was designed to:

  • measure ventilation, CO₂, and respiratory balance

  • automatically detect the two ventilatory thresholds

  • work without calibration

  • be used freely outdoors (cycling, running, home trainer)

  • display your training zones in minutes


This brings a scientific approach—previously reserved for laboratories—to every athlete.



In summary


Ventilatory thresholds allow you to:

  • understand your metabolic transitions

  • target the right intensities

  • build smarter training sessions

  • improve performance while reducing unnecessary fatigue


👉 If you want to know your true physiological zones, respiratory analysis is the most reliable method.



 
 
 

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