The Science of CO2 Tolerance Training With MAXIMUS

You Never Forget How to Ride a Bike.  You Won't Forget This, Either.

Why CO₂ tolerance training is the only breath work you do once.

Get on a bicycle today, even if you haven't touched one in twenty years. Your body will know what to do.

You won't think about it. You won't rehearse it. You'll push off, wobble for half a pedal stroke, and ride. The wiring is still there — buried in your cerebellum, written into your nervous system the summer you were six years old, and entirely indifferent to the two decades you spent not using it.

That isn't muscle memory. Muscle memory detrains. The quads you built in college are long gone. What stayed is neural memory — a learned coordination pattern encoded so deeply into the brain that the body doesn't have to relearn it. You did the work once. You kept the result.

This is the part of the breathing-trainer conversation almost no one is having. And it's the part that matters most.

Every other breath trainer asks you to train forever

Pick up any inspiratory muscle trainer — PowerBreathe, Bas Rutten's O₂ Trainer, the whole category. They work by making your respiratory muscles work harder. Diaphragm. Intercostals. The same way a dumbbell works your biceps.

And like your biceps, those muscles obey one rule above all others: use it or lose it.

Stop training for three months and your respiratory strength regresses. Six months and most of the gain is gone. A year and you're back where you started. This is not a flaw of the products. It's the nature of skeletal muscle. Cardiovascular fitness behaves the same way — ask any athlete what happens to their VO₂ max during an off-season they don't manage carefully.

So the implicit deal with a muscle-based breathing trainer is the same deal you have with any gym membership: you pay, in time and effort, forever. The day you stop is the day the clock starts running backward.

That's not the deal Maximus is offering.

CO₂ tolerance is a neural adaptation, not a muscular one

Here's where the bike analogy stops being cute and starts being literal.

When you train CO₂ tolerance — really train it, by deliberately accumulating CO₂ in the blood during exercise until the body learns to tolerate higher levels without panic — you are not strengthening a muscle. You are recalibrating the brainstem.

Specifically, you're resetting the sensitivity of the chemoreceptors that monitor CO₂ in your bloodstream. Those receptors are the panic alarm of the respiratory system. In an untrained person, the alarm goes off at a low threshold: a tiny rise in CO₂ triggers the urge to breathe, then anxiety, then full-blown hyperventilation. In a trained person, the alarm threshold has been raised. The body has learned, at the level of the neural circuit itself, that this level of CO₂ is not an emergency.

This is the same kind of adaptation that lets you ride a bike. Not in the cerebellum — in the brainstem. But the same neural class. The same permanence.

The respiratory neuroplasticity literature has been pointing at this for two decades now. When the brainstem rewires its set-point, that rewiring is durable in ways skeletal-muscle adaptations simply are not. The published evidence suggests these adaptations persist long after active training tapers off. The chemoreceptor reset, once achieved, doesn't reset back.

You do the work once. You keep the result.

What this looks like in practice: one founder's longitudinal data

I'll be transparent about what this is and isn't: what follows is not a clinical trial. It's the founder of Maximus, Jamie Mueller, on himself, over five years, measured with the same Polar wearable the whole time.

But it's real longitudinal data, the kind almost no one in the wellness space actually keeps, and it tells a story worth listening to.

Jamie is 61 years old. His VO₂ max is 42 ml/kg/min, which puts him in the elite classification for his age group. That number, in itself, is interesting. What's remarkable is that the number has stayed in elite territory for over four years on minimal, summer-only training.

If VO₂ max were a purely muscular and cardiovascular adaptation, that shouldn't happen. A 61-year-old who barely trains nine months of the year would see meaningful regression season over season. The data should look like a slow decline.

It doesn't. It looks flat. Elite-flat.

The most parsimonious explanation, the one that fits both the data and the underlying neuroscience, is that the ventilatory adaptations he built during active CO₂ tolerance training didn't decay during his off-seasons, because they were never stored in his muscles in the first place. They were living in his brainstem. And brainstem wiring, like bicycle wiring, doesn't ask for a monthly renewal.

This is a sample size of one. We'll be the first to say it. But it's a sample size of one that's been carefully measured for half a decade, and the trajectory is what the neuroscience would predict if the mechanism really is what we believe it is.

The economics of a one-time adaptation

Step back from the physiology for a second and consider what this means for you, the person deciding how to invest your time.

Every other breathing trainer is a subscription on your calendar. Not a financial subscription — a biological subscription. The minute you stop showing up, the body starts undoing the work.

CO₂ tolerance training is fundamentally different. You're not renting a result. You're buying one. Do the work, achieve the chemoreceptor reset, and the adaptation is yours to keep. Maintenance work is welcome, of course, but the foundation doesn't crumble the moment you take a break.

That's why we built Maximus the way we did. Dual-resistance airflow under exercise load deliberately drives the CO₂ accumulation that triggers the brainstem to recalibrate. Not a muscle trainer.

Not a relaxation tool.  A device designed around the one breathing adaptation that's actually permanent.

You learned to ride a bike once

You didn't have to relearn it every spring. You did the work, the wiring formed, and the wiring stayed.

The same physics, the same neuroscience, really, applies to the way your body decides how much CO₂ counts as an emergency. Train that threshold once with the right stimulus, and the recalibration is yours.

Get on the bike. Push off. Your body knows.