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The oxygen you breathe has one destination: your mitochondria. There it becomes water, carbon dioxide and ATP— energy. When that conversion is inefficient, every system is affected.

VO₂ max — the highest rate at which you can use oxygen — is one of the strongest modifiable predictors of all-cause mortality and healthy lifespan we have. In a meta-analysis of 33 studies and more than 100,000 people, each 1-MET rise in cardiorespiratory fitness (roughly 3.5 mL/kg/min of oxygen use) was associated with a 13% lower risk of death from any cause and a 15% lower risk of coronary or cardiovascular events.

That is why we measure it. It is also why one number is not enough.

A VO₂ max score tells you the ceiling. It does not tell you whether the limiter is the lungs, the heart, the circulation or the cells — or where ‘easy’ actually stops being easy. PNOĒ’s VO2 Max breath analysis publishes 23 cardio-metabolic biomarkers from the same test. This article is a field guide to those 23 signals, written for clients, trainers and anyone considering Core Naturopathics’ signature Metabolic, Longevity and Performance Assessment.

Why breath, not another wrist estimate

Wearables estimate. A metabolic assessment measures. PNOĒ VO2 Max is a portable cardiopulmonary exercise test: oxygen in, carbon dioxide out, airflow, and heart rate, captured breath by breath at rest and under a graded load.

That combination is how physiology laboratories have assessed aerobic metabolism for decades. The difference for clinic use is time and access. The resting test (RMR) is done seated and fasted. The active test (AMR / VO₂ max) is a guided ramp on a bike or treadmill. Analysis is immediate. There is no blood draw for the breath panel itself.

The oxygen chain — four jobs, 23 numbers

Lungs and breathing (1–9). How much air you move, how fast you breathe, and how efficiently that air exchanges oxygen and carbon dioxide. Keep ventilation economical as work rises.
Heart and circulation (10–13). Whether the pump and the blood can deliver the oxygen the lungs just took in. Deliver the oxygen the lungs just loaded, beat by beat.
Metabolism and fuel (14–21). Whether the cells can use the oxygen that arrived —and which fuel they choose. Use that oxygen in the mitochondria. Choose fat or carbohydrate. Do mechanical work without wasting energy.
Thresholds (22–23). The two turning points of the oxygen chain under load,
as heart rate and intensity. Mark where easy stops being easy (VT1) and where hard stops being recoverable (VT2).

A problem in one block almost always shows up as a compensation in another. That is why we do not base program recommendations from VO₂ max alone. Over-breathing can make heart rate and RER look ‘hot’ for the workload. A flat O₂ pulse means the cells never see enough oxygen to stay with fat burning. A low FatMax usually pulls VT1 down into everyday life, so every session feels like a grind.

Lungs and breathing — biomarkers 1–9

This block answers a simple question: can you move and exchange gas well enough for the work asked of you?

A healthy pattern, as fitness rises, is fewer and larger breaths, with VE/VCO₂ staying economical and end-tidal CO₂ holding rather than crashing. The opposite pattern — a high rate, a small tidal volume, a rising VE/VCO₂ — is why some people feel wrecked at intensities their legs could have handled.

1. Breathing frequency (BF): Breaths per minute at rest and as work rises. A high rate for the work usually means shallow or inefficient breathing. Improving it can ease air hunger and raise the pace you can hold.

2. Tidal volume (VT): Air moved in a single breath. Small tidal volume plus a high rate is a common limiter. Breath, posture and rib-cage mobility can raise delivery without extra strain.

3. Minute ventilation (VE): Air moved in one minute (rate × tidal volume). Shows whether the lungs are keeping up with demand. Used to set zones and to spot early ventilatory limitation.

4. Forced expired volume (FVC/ FEV): Largest volume you can empty in a prolonged exhalation at rest. A low value can flag restricted or obstructed breathing and explains why some people ‘run out of air’ before the legs do.

5. VE/VCO₂ (ventilatory efficiency): Air you must move to clear each unit of carbon dioxide. A high ratio means the lungs or circulation are working harder
than they should. Used in rehab and in endurance programming.

6. End-tidal CO₂ (FetCO₂): Peak carbon dioxide at the end of a breath. Low or falling FetCO₂ can mean over-breathing or poor gas exchange. Relevant to dizziness, air hunger and pacing.

7. End-tidal O₂ (FetO₂): Oxygen at the end of the breath cycle. Helps show how completely you are extracting oxygen from each breath.

8. Fraction of expired CO₂ (FeCO₂): Average carbon dioxide in one exhalation. Used with VE and VCO₂ to judge whether ventilation matches metabolism.

9. Fraction of expired O₂ (FeO₂) Average oxygen in one exhalation. Together with VO₂, this is extraction at the lung — the first step of the oxygen chain.

Heart and circulation — biomarkers 10–13

This block answers: can the pump deliver what the lungs just loaded?

Heart rate on the day becomes the language of your zones. Two people with the same VO₂ max can have VT1 fifty beats apart. Programming them on the same percentage of max is how one person adapts and the other accumulates fatigue.

O₂ pulse — oxygen used per heartbeat — is the quiet workhorse of this block. As work rises, a healthy O₂ pulse usually rises with it (more blood ejected, more oxygen extracted). A flattening or falling O₂ pulse is a reason to slow down the conversation, check symptoms and, where indicated, involve a medical practitioner. This test is not a substitute for a cardiologist’s stress test.

HRV in this context is not a morning readiness score from a ring. It is beat-to-beat variation captured around the metabolic test — a window on whether the autonomic system still has reserve under load.

10. Heart rate: Beats per minute through the test. Thresholds are set to your heart rate, not a 220-minus-age formula. That is how zones become personal.

11. Heart rate variability (HRV): Beat-to-beat variation — a window on autonomic tone. Low HRV under load or at rest can mean the system is still
defending rather than recovering. Useful for pacing weeks, not just sessions.

12. O₂ pulse (VO₂ / HR): Oxygen used per heartbeat — a proxy for stroke volume and extraction.

A flat or falling O₂ pulse as work rises can point to cardiac or peripheral limitation. A rising O₂ pulse is a healthy training response.

13. VO2/breathing frequency: Oxygen taken up per breath. Separates ‘lungs not keeping up’ from ‘heart or cells not using the oxygen’. Guides whether breathwork or aerobic base is the first lever.

Metabolism and fuel — biomarkers 14–21

This block answers: can the mitochondria use the oxygen, and which fuel are they on?

Mitochondrial capacity is not abstract. It is the reason two 48-year-olds can walk the same coastal path and only one of them needs a sit-down at the top. Capacity starts to drift in the thirties. By the mid-fifties most people can feel it — slower recovery, stubborn weight, training that no longer pays them back — unless they have been measuring and training the chain.

RER is the ratio of carbon dioxide produced to oxygen consumed. Near 0.70 the cells are leaning on fat. Near 1.00 they are leaning on carbohydrate. At rest, a high RER can mean you are still paying yesterday’s session, or that fat oxidation is simply low. Under load, the same ratio traces the shift from FatMax toward the crossover and then toward VT2.

Fat oxidation and the crossover are why ‘Zone 2’ only works when it is your Zone 2.

FatMax is the intensity where fat use peaks — often near, but not identical to, VT1. Spending time there is how metabolic flexibility is usually rebuilt. Spending most of the week above the crossover is how people stay tired and still do not get leaner.

Mechanical efficiency is the unfashionable number that often explains a plateau. If you spend more energy for the same pace than you did twelve weeks ago, the issue may be skill, strength, sleep or accumulated load — not ‘more intervals’.

14. VO₂ peak / VO₂ max: Highest oxygen use on the test, usually as mL/kg/min. The strongest single cardiorespiratory marker we have for healthspan and all-cause risk. A target to train — not a vanity score.

15. VCO₂: Carbon dioxide produced each minute. CO₂ rises as intensity and carbohydrate use rise. It is the other half of the fuel and ventilatory picture.

16. Respiratory exchange ratio (RER): VCO₂ ÷ VO₂. Near 0.70 is fat-dominant; near 1.00 is carbohydrate-dominant. Shows which fuel you are on at rest and at each intensity. High resting RER can mean low fat oxidation or incomplete recovery.

17. Caloric burn: Calories used per minute at rest and during the ramp. Replaces guesswork from watches. Describes energy demand.

18. Fat oxidation: Grams and calories of fat used per minute. Identifies FatMax — the intensity where fat use peaks. The workhorse zone for metabolic flexibility and a durable aerobic base.

19. Carbohydrate oxidation: Grams and calories of carbohydrate used per minute. Shows when you tip onto sugar. Explains why some efforts
feel costly and how long work should be fuelled.

20. Mechanical efficiency: Work produced relative to calories burned. Poor efficiency means more energy for the same pace. It often improves with skill, strength and aerobic base — and it flags accumulated fatigue.

21. Crossover point: Heart rate where fat and carbohydrate oxidation are equal.

The landmark between easy aerobic work and mixed fuel. Training below it builds the base; work above it is more glycolytic.

Thresholds — biomarkers 22–23

This block answers: where does easy stop being easy, and where does hard stop being recoverable?

VT1 — the first ventilatory threshold, also called the aerobic threshold — is the heart rate where fatigue starts to accumulate at a still-sustainable rate. It is the ceiling of true easy aerobic work. Most recreational athletes live above it by habit. Holding work near VT1 is how VO₂ and fat oxidation usually rise without burying recovery.

VT2 — the second ventilatory threshold, also called the anaerobic threshold — is the heart rate where fatigue accumulates faster than you can clear it. Intervals live around and above it. Most of the week should stay below it unless the plan says otherwise.

The report turns VT1 and VT2 into heart-rate zones. That is the document your trainer can actually use — provided you have signed consent for us to share it.

22. Aerobic threshold / VT1: First ventilatory threshold — the heart rate where
fatigue starts to accumulate at a still-sustainable rate. Your true Zone 2 ceiling. Most people train above this by accident. Holding work near VT1 is how VO₂ and fat oxidation usually rise.

23. Anaerobic threshold / VT2: Second ventilatory threshold — the heart rate where fatigue accumulates faster than you can clear it. The red line for sustainable intensity. Intervals live around and above it. Most of the week should stay below it unless the plan says otherwise.

What the test day actually looks like

You complete a PAR-Q and the PNOĒ questionnaire before we confirm the booking. If you have cardiovascular, respiratory, metabolic or other chronic conditions, physician clearance may be required. Take prescribed
medicines as directed. Bring asthma or heart medicines with you. If you are unwell — fever, chest infection, acute injury — we reschedule.

Resting test (RMR). Fast at least three hours (water is fine). No caffeine, tobacco or stimulants for three hours. No intense exercise longer than an hour in the previous 24 hours. Sit quietly. Breathe through the mouthpiece. The work is stillness.

InBody 580  measured next for muscle, fat, visceral fat, phase angle and fluid.

Active test (AMR / VO₂ max). A light snack three hours before is acceptable. Same stimulant and heavy-exercise rules. Athletic clothing and training shoes suitable for the bike. We guide a warm-up, a graded ramp to a hard but supervised effort, and a cool-down. The maximal portion is typically eight to fifteen minutes.

Arrive ten minutes early so you are not starting from the car park. Chest pain, unusual breathlessness or a change in medical status belongs with your doctor before you book.

What you leave with

The 23 biomarkers are not the deliverable. The deliverable is a picture of the limiting system, plus heart-rate zones built from your thresholds rather than a formula detailed in your reports.

The PNOĒ report scores aerobic capacity, fat-burn efficiency, heart and lung fitness and recovery. Optional add-ons — i-SCREEN cardiovascular pathology and MeScreen mitochondrial efficiency assessment — fill biochemical and cellular layers the breath test cannot see.

Review is a thirty-minute conversation once reports are in the file, usually three to five days after testing (longer if a blood panel is pending). You come ready to look at numbers and leave with a plan for your trainer or Coach. Trainers receive a summary only with your signed consent.

Improving VO₂ max, fat oxidation and ventilatory efficiency is associated with better cardiorespiratory fitness and lower long-term risk in large cohort studies. That is a population finding. It is not a promise about your next twelve weeks. Change is built by the work you do between tests.

Who this is for — and who should wait

Athletes and active people who want FatMax and Zone 2 that belong to them, not another guess at heart-rate zones.
Adults 35 and over who want an objective biological-age and longevity marker they can actually train.
Anyone stuck on a weight, energy or performance plateau who would rather measure before they overhaul.

Wait — and speak to your doctor first — if you have unstable cardiovascular disease, uncontrolled respiratory or metabolic disease, an acute infection or injury, or any symptom that would make a maximal effort unsafe. A PAR-Q is a screen, not a clearance.

Core Naturopathics offers this as our signature Metabolic, Longevity and Performance Assessment in Wollongong, for our own clients and on referral from trainers, coaches and allied health. The Assessment service does not include dietary advice. A separate Performance Package can add app-based nutrition and training recommendations, with an optional thirty-minute naturopathic consult.