Skip to content

The science

Your breath is the measurement.

Every breath carries a record of how hard your body is working. Here is how VenTracer reads it, and what the numbers on your report mean.

V-slope · VCO₂ against VO₂ · simulated

In short

Two answers before the detail.

How does a breath analyzer measure VO₂max?

It measures how much air you breathe each minute and how much oxygen is missing from the air you breathe out, then multiplies the two, breath by breath, with corrections for temperature, pressure and humidity. During a ramp test to exhaustion, the highest sustained value is your VO₂max.

What are VT1 and VT2?

VT1, the first ventilatory threshold, is where breathing starts rising faster than oxygen use: roughly the top of easy endurance pace. VT2, the respiratory compensation point, is where breathing rises sharply again: above it, effort lasts minutes, not hours.

Film · 25 s · original score

One breath, measured.

Flow, then gas, then the maths, then the ramp: how one exhale becomes a point on your VO₂ curve.

Illustrative signals, not measured data. Plays muted until you press Play with sound, or turn on site sound.

VO₂max

The size of your aerobic engine.

VO₂max is the highest rate at which your body can take in and use oxygen. It sets the ceiling for every endurance effort, and it's one of the strongest fitness markers linked to long-term health.

You can't measure it from heart rate. You have to measure the oxygen that goes in and the oxygen that comes out, and the volume of air carrying it. That's what a metabolic cart does in a lab, and what VenTracer is being built to do on your face.

The core equation

VO₂ ≈ V̇E × (F_IO₂ − F_EO₂)

V̇E: Ventilation: litres of air you breathe each minute. Measured by the breath flow sensor.
F_IO₂: Oxygen fraction in the air you breathe in: about 20.9% at any altitude.
F_EO₂: Oxygen fraction in the air you breathe out. Measured by the dual-gas breath core.

Simplified. The full calculation corrects for the difference between inhaled and exhaled volume (the Haldane transformation) and for temperature, pressure and humidity.

Thresholds

Find where your breathing breaks.

On a ramp test, oxygen uptake climbs steadily with power. Carbon dioxide output and breathing don't. At VT1, CO₂ output and breathing start rising faster than oxygen uptake. At VT2, breathing starts outpacing even CO₂ output. Those two breaks are your ventilatory thresholds, and they set your training zones.

Hover or tap the chart to read a point. Simulated example athlete.²

VT1

The conversation line. Breathing starts rising faster than oxygen use. Below it you can hold effort for hours.

VT2

The redline. Above it breathing climbs faster than CO₂ output and end-tidal CO₂ falls. Effort lasts minutes, not hours.

Moderatebelow 210 W

Heavy210–312 W

Severeabove 312 W

Physiologists find VT1 with the V-slope method: plot CO₂ output against O₂ uptake and look for the break. The VenTracer mark is drawn from that bend.

For physiologistsHow VenTracer will compute it

Breath detection: Breaths are split at flow zero-crossings, with checks that reject swallows, coughs and partial breaths.
Gas–flow alignment: Gas readings are time-shifted to match the flow signal before each breath is integrated.
VO₂ and VCO₂: Computed per breath from expired fractions and ventilation, using the Haldane transformation for inspired volume.
Corrections: Ventilation reported at BTPS, gas volumes at STPD, using on-board pressure, temperature and humidity.
VT1: V-slope method, cross-checked against the rise in VE/VO₂ without a rise in VE/VCO₂.
VT2: Respiratory compensation point: the rise in VE/VCO₂ and fall in end-tidal CO₂.
VO₂max: Highest rolling average with a plateau check; flagged as VO₂peak when no plateau is seen.
Raw data: Every breath exportable with time, flow, gas fractions and derived values for your own analysis.

Planned methods. Final algorithms will be described in the validation publication.³

Test protocols

How to run a VO₂max ramp test: three protocols.

Every protocol does the same thing: start easy and increase the load steadily until you can't continue. The app will guide each one.PRELIM

Cycling · indoor trainer

Power ramp

10 min easy warm-up
Start around 100 W
Add 20–30 W each minute
Ride until you can't hold cadence

Most repeatable. Thresholds come out in watts.

Running · treadmill or track

Speed ramp

10 min easy jog
Raise speed every minute
On a treadmill, add incline near the end
Run to voluntary exhaustion

Thresholds come out as pace and heart rate.

Field · any sport

Stepped effort

Warm up as you normally would
Hold each step for 2–3 min
Raise intensity each step
Finish with a maximal effort

For rowing, skiing, team sports and clinic sessions.

Maximal testing is hard work. Talk to a doctor first if you have a heart, lung or other medical condition, or aren't sure hard exercise is safe for you.⁴

Glossary

VO₂max, VT1, VT2 and RER: the words on your report.

VO₂L/min · ml/kg/min: Oxygen uptake: how much oxygen your body uses each minute. Divided by body mass, it's comparable between athletes.
VCO₂L/min: Carbon dioxide output: how much CO₂ you breathe out each minute.
RERratio: Respiratory exchange ratio, VCO₂ ÷ VO₂. At steady state, near 0.7 means mostly fat and near 1.0 mostly carbohydrate. Near and above VT2, RER rises above 1.0 from CO₂ buffering, not fuel.
V̇EL/min: Minute ventilation: the total air you breathe each minute. Breathing rate × tidal volume.
VT1threshold: First ventilatory threshold. Breathing starts to rise faster than oxygen use. Roughly the top of all-day endurance pace.
VT2threshold: Second ventilatory threshold, or respiratory compensation point. Above it, effort can be held for minutes, not hours.
V-slopemethod: Plotting VCO₂ against VO₂ and finding where the slope steepens. A standard way to find VT1, usually confirmed with ventilatory equivalents, and the source of the VenTracer mark.
VO₂peakvalue: The highest VO₂ reached in a test when oxygen uptake didn't clearly plateau. Reported separately from VO₂max.
Ventilatory equivalentsVE/VO₂ · VE/VCO₂: Air breathed per litre of oxygen used or CO₂ produced. Their changes confirm where each threshold sits.
BTPS and STPDcorrections: Standard conditions. Ventilation is reported at body temperature and pressure, saturated; gas volumes at standard temperature and pressure, dry.
Fat maxW · pace: The intensity where you burn the most fat per minute, estimated from RER during steady-state stages. A fast ramp gives only a rough guide.
Breath by breathsampling: Every breath is measured and stored on its own, rather than averaged over a mixing chamber.

Further reading: Beaver, Wasserman and Whipp, “A new method for detecting anaerobic threshold by gas exchange”, Journal of Applied Physiology, 1986, the original description of the V-slope method.

Physiologist? We want your eyes on this.

Help shape the methods and the validation study before the first units ship.

Apply as a pilot partner For labs and clinics