MAXIMUS DESIGNED FOR CO2 Tolerance Training

MAXIMUS DESIGNED FOR CO2 Tolerance Training

Jamie Mueller · CO₂ TOLERANCE TRAINING

For five decades, sports science has mastered three pillars of physical training. Cardiac output: trained. Muscular strength: trained. Mitochondrial efficiency: trained. We have devices, protocols, wearables, and entire industries built around each one.

There is a fourth pillar nobody trains. It limits your VO₂ max more than the other three combined. It's the reason you gasp at minute six of a hard run when your legs still feel fresh. It's why anxiety hijacks your breath. It's the silent ceiling on respiratory performance, and until recently, it was considered untrainable.

It's called CO₂ tolerance, and it's the central concept behind a new category of training that's about to become as foundational as strength training was in the 1970s. The category is called CO₂ Tolerance Training. The device that pioneered it is called MAXIMUS.

What CO₂ Tolerance Actually Is

Most people assume the urge to breathe comes from running out of oxygen. It doesn't. The urge to breathe comes from rising carbon dioxide.

Deep in your brainstem, in a region called the retrotrapezoid nucleus, lives a population of neurons that act as chemoreceptors. They constantly measure the CO₂ level in your blood. When CO₂ rises past a certain threshold, those neurons fire a signal that becomes the conscious sensation we call “I need to breathe.” If you've ever held your breath underwater, the panicky urge you felt at thirty seconds wasn't oxygen depletion — it was your chemoreceptors firing.

The problem is that in most adults, those chemoreceptors fire too early. They're calibrated to a low CO₂ threshold. The result: your breathing pattern falls apart during exercise long before your cardiovascular system reaches its actual limit. You hit a ventilatory ceiling at maybe 75% of your true capacity. Your cardiac output gets throttled. Your stroke volume — the amount of blood your heart pumps per beat — never reaches what it could be.

CO₂ Tolerance Training recalibrates the chemoreceptor threshold. You teach your brainstem to tolerate higher CO₂ before triggering the panic-breathing response. The threshold moves. The ventilatory ceiling lifts. Stroke volume rises. VO₂ max climbs.

The Four Things You Train

Real CO₂ Tolerance Training works on four interconnected systems simultaneously:

1. CO₂ Tolerance. The central adaptation. Your brainstem learns to tolerate higher CO₂ before signaling distress. This is the master switch that unlocks everything else.

2. Stroke Volume. When your chemoreceptors stop hijacking breath, your heart fills more completely between beats. Each beat pumps more blood. Cardiac output rises without your heart rate having to increase — the elite endurance adaptation, achieved through breathing protocol instead of years of zone-two training.

3. Chemoreceptor Plasticity. The neural rewiring itself. Peer-reviewed research on respiratory neuroplasticity (PMC4578297 and the broader literature on long-term facilitation of breathing) shows that repeated hypercapnic stimulus produces measurable, lasting changes in the respiratory control system. Unlike most fitness adaptations, this one doesn't decay quickly when training stops.

4. Ventilatory Threshold. The practical endpoint. The wattage, pace, or workload at which your breathing falls apart. CO₂ Tolerance Training raises this threshold, which is what wearables actually measure when they show your VO₂ max climbing.

How You Train It

You can't train CO₂ tolerance with conventional exercise. Running harder doesn't do it — running harder forces you to breathe more, which keeps CO₂ low. To train the chemoreceptor threshold, you need to do the opposite: produce a controlled, calibrated rise in CO₂ during exercise.

That's what MAXIMUS does, and why no conventional breathing device produces the same adaptation.

MAXIMUS is a patented hypercapnic trainer worn during exercise — cycling, running, rowing, HIIT, and resistance training. It applies dual airflow resistance and equalizes load on both inhale and exhale, using a proprietary mechanism called Dual Airflow Resistance Technology (DART). The combination is unique: every other breathing trainer on the market restricts inhale-only or exhale-only, or is designed to be used while sitting in a chair. MAXIMUS is the only device to deliver calibrated bidirectional resistance during real exercise, the specific condition that drives chemoreceptor adaptation.

You wear it for 35–45 minutes, two or three times a week, during workouts you're already doing. The device has nine resistance levels — from 25% airflow restriction for beginners up to 96% for elite athletes who've outgrown every other trainer. There's no app, no battery, no subscription. It's a one-ounce mechanical device that does to your respiratory system what compound lifting does to your skeletal muscle.

Pick a level where you feel real respiratory load but can still complete the workout. Use it consistently for 60–90 days. Most users feel meaningful change within four weeks. Wearable data — Garmin, Polar, WHOOP, Apple Watch — typically shows VO₂ max climbing within eight to twelve weeks.

Why the Adaptation Sticks

This is the most important part of CO₂ Tolerance Training, and the part the rest of the breathing-device industry can't match. Most fitness adaptations decay fast. Stop training cardio and you lose half your aerobic gains within a few months. Stop strength training and your muscle loss is measurable within weeks.

Chemoreceptor recalibration is different. It's a neural adaptation, encoded in the brainstem itself, not a muscular or cardiovascular one. The published literature on respiratory neuroplasticity suggests these adaptations persist long after active training tapers off.

The founder of MAXIMUS, Jamie Mueller, has five years of personal longitudinal Polar Own/Index data demonstrating exactly this: his VO₂ max has remained in the ELITE classification for age (42 ml/kg/min at age 61) for over four years on summer-only, minimal training. The chemoreceptor reset, once achieved, doesn't reset back.

That changes the economics of the practice entirely. Other breathing trainers ask you to use them forever to maintain gains.

Think about learning to ride a bike. You did it once, maybe at six years old. You haven't ridden in twenty years. Get on a bike today — your body still knows. That's not muscle memory. That's a permanent rewiring of your cerebellum, encoded into the nervous system in a way that simply doesn't decay.

CO₂ Tolerance Training produces the same kind of adaptation. Not in the cerebellum, but in the brainstem. Same neural permanence. Same “do the work once, keep the result.” Other breathing trainers train muscles, which detrains.  MAXIMUS trains the nervous system, which doesn't detrain.

Why This Is the Last Frontier

CO₂ Tolerance Training matters now because the rest of the field has matured. The remaining gains in human performance live in the system nobody trained: the respiratory control mechanism itself.

Every major wearable now measures VO₂ max. Every serious athlete tracks it. Every longevity researcher cites it as the single most modifiable predictor of health-span. The metric matters. What's been missing is a way to move it deliberately — through a protocol, with a device, in a way the science supports.

MAXIMUS fills that gap. It's the only patented device designed specifically to recalibrate CO₂ tolerance during exercise. It's the only training tool with peer-reviewed mechanism support and multi-year longitudinal user data. It's the device that defined the category.

Breathwork is the last frontier in human performance. MAXIMUS pioneered CO₂ Tolerance Training — the only training that recalibrates the brainstem reflex, limiting your VO₂ max.

Train it once. Keep it for years.

Learn more at trainmaximus.com