CO2 is not what you think it is. Neither is your pump pre-workout.

A few years ago I watched a very fit, very serious athlete fall apart in a repeated sprint test like a luxury sedan losing all four wheels on the freeway.

On paper, he looked bulletproof.

Strong.
Lean.
Well-trained.
The kind of athlete who makes coaches say stupid things like, “Yeah, he can handle anything.”

Except he couldn’t.

First 60 sec sprint on the Concept 2 evil rower looked good.
Second sprint looked fine.
Power at the start of each effort stayed respectable.

Then the rest periods got shorter.

By sprint four, the machine was reading numbers that looked less like a trained athlete and more like a 14 year old golden retriever half-heartedly chasing a tennis ball in July.

His oxygen wasn’t the problem.

CO2 was the issue.

And that matters, because the fitness world still treats CO2 like trash gas.

Exhaust.

Smoke.

Something to dump overboard as fast as possible.

Wrong.

CO2 helps tell hemoglobin to let go of oxygen.

Without that signal, oxygen can ride around in the bloodstream like a smug little billionaire in a limousine while your muscles are two feet away, broke, desperate, and ready to riot in the streets.

This is called the "Bohr Effect" in 1904 by the Danish physiologist Christian Bohr. Creative bastard on the name!

This went down more than a century ago and somehow most coaches still talk about breathing like they learned physiology from an IG GooRoo who only follows the nekkid grocery getter in Costa Rica for his info.

Here’s the practical version:

Hemoglobin does not release oxygen just because you want it to.

It needs a reason.

Rising CO2 in working tissues is one of the big reasons.

More CO2 shifts the oxygen-hemoglobin dissociation curve and helps oxygen unload where the work is actually happening.

Now take the athlete who starts breathing too fast (over breathing).

CO2 drops.

pH rises toward alkalosis.

Hemoglobin tightens its grip.

Less oxygen gets delivered to tissue.

That athlete feels like he’s “getting plenty of air,” while his working muscles are slowly getting stiff-armed in the parking lot.

That’s the hyperventilation paradox.

You can literally breathe yourself into worse performance.

And here’s where it gets even more fun:

CO2 also acts as a vasodilator.

In plain English, that means it helps open blood vessels and improve blood flow.

So your favorite pre-workout pump powder — the radioactive scoop of citrulline, beetroot, and branding written by a man named Kyle with a neck tattoo — is trying to do with neon dust what better CO2 handling can help do for free.

That should annoy you.

It annoys me.

And again, there is some data on those ingredients, but if your breathing like a raccoon trapped in a trombone, you are F-ed for starters and all the beetroot in the world won't help.

Most people roaming the purpled encased walls of PF walking to nowhere doing Zone 2 on the treadmill also get the drive to breathe wrong.

They assume the urge comes from low oxygen.

Nope.

The main trigger is rising CO2, not oxygen.

That means CO2 tolerance — your ability to sit with that rising signal without panicking and breathing— is one of the most trainable variables in the whole respiratory system.

And almost nobody trains it on purpose.

Test It Yourself

Brian MacKenzie at Shift Adapt uses a simple Nasal Exhale test you can look up, but it goes like this:

Inhale, then on the next exhale, only exhale through your nose as long as you can.
Hit start on a timer right as you exhale.
Hit stop if you have to swallow or can no longer exhale or pause at any point.

Write that number down.

If you’re under 20 seconds, your CO2 tolerance is doing a beautiful impression of a wet paper bag around your results.

The good news?

That number can improve.

And when it does, recovery between hard efforts improves too.

Oxygen delivery gets better.

pH control under load gets less sloppy.

You stop crumbling the second the work turns ugly.

This matters for aerobic work and for higher rep lifting sets.

Any time you are suffering more, this matters even more.

When I built the Phys Flex Cert, I originally tried to cram a full aerobic development system into it.

Then I realized I was stuffing 17 lbs of stuff into a 5 lb brown bag, so I split it off into what became Meathead Cardio - Level 1 and Level 2 - in order to do it full justice.

These systems are related and in the Phys Flex Cert I do a ballZ deep dive into how your body regulates O2 and CO2 for performance and health.

Again, all systems in physiology are related as your aerobic development feeds CO2 tolerance too.

It feeds pH buffering too.

These systems talk to each other whether you understand them or not.

That’s why I am adding a NEW bonus - the Meathead Cardio Quick Start Guide is yours at no cost when you enroll in the Phys Flex Cert before cart close Monday, April 27 at midnight PST.

The full Red Light video series bonus is still active too.

​Inside the Phys Flex Cert, I give you the full CO2 tolerance playbook:

-the right way to test it,
-progressive ways to train it,
-where it plugs into pH work,
-how temperature exposure changes the game,
-and why breathing is not some optional wellness garnish sprinkled on top of real training.

Because once you understand what CO2 is actually doing, you stop coaching breathing like a yoga side quest and start using it like the performance tool it really is.

​https://miket.me/physflex <-- full details

Payment plans are live at checkout via Affirm and Klarna.

Much love and vasodilation,
Dr. Mike

PS — “Dr. Mike’s PFC course kept me ahead of the trends and has given me the ability to make direct and practical decisions for each of my athletes.

Whether you are wondering about the keto diet all the way to the hot trend of ice baths — Dr. Mike sets you up in the best position to make practical and real world decisions on how to manage the body.

PFC is a game changer. PFC is practical.

PFC was an easy decision for me.”
— Jocelyn Awe, Director of Sports Performance, Whitman College

​https://miket.me/physflex <-- full details

PPS — Stay tuned for a brand new podcast with breathing coach Martin McPhilliey to go deep on the practical side of this mess: CO2 tolerance, nasal breathing, breath holds, and what actually works when the athlete is cooked and the stopwatch is still running. Once this new podcast is done I will send it to you here.

____________________

Mike T Nelson CISSN, CSCS, MSME, PhD
Associate Professor, Carrick Institute
Owner, Extreme Human Performance, LLC
Editorial Board Member, STRONG Fitness Mag

Mike T Nelson is a PhD and not a physician or registered dietitian. The contents of this email should not be taken as medical advice. It is not intended to diagnose, treat, cure, or prevent any health problem - nor is it intended to replace the advice of a physician. Always consult your physician or qualified health professional on any matters regarding your health.

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