Stop worshipping at the soft blue altar of Zone 2 cardio.
According to the internet mitochondrion GooRoos, apparently everyone now needs 2-3 hours of nasal-breathing monk laps or your body will file a grievance with the longevity gods.
A narrative review in Sports Medicine from Storoschuk, Moran-MacDonald, Gibala, and Gurd (2025), walked into the Zone 2 temple carrying a gas can and a lit Marlboro.
The claim?
Zone 2 is the optimal intensity for building mitochondria.
That claim does not survive contact with the actual data by hardcore nerds.
The signaling evidence was small, inconsistent, or missing like a gym owner when the HVAC bill shows up.
They did find that harder efforts above Zone 2 did more for mitochondrial adaptation and cardiorespiratory fitness.
This is great news specially when your training time is limited and you are not living inside a Scandinavian endurance lab with unlimited daylight, fermented fish, and a lactate meter glued to your hand.
Translation: Zone 2 cardio is not magic.
Several longevity influencers may now spill their electrolyte water into their cold plunge and can safely remove the red light from their keester.
They highlighted another issue:
Zone 2 may fall below the moderate-intensity threshold used in physical activity guidelines.
If you trade all your harder cardio for easy nose-breathing laps because a podcast told you "mitochondria Bro," you might be leaving the biggest health returns on the table.
That is not "optimization".
It is underdosing dressed up as precision guided BS on a pogo stick.
Now, before the Zone 2 zealots start clawing drywall, yes — Zone 2 has value.
Easy aerobic work can help fat oxidation.
Recovery cost stays low.
Untrained, overweight, beat-up, or low-capacity humans can use it as a smart entry point..
..but it is absolutely not the glowing mitochondria chalice of eternal life.
Want my free cardio protocol that actually matches the evidence and does not require you to cosplay as a retired Tour de France domestique?
Comment CARDIO below and I'll send it to you. It starts at only 6 minutes per day.
Much love and bigger engines,
Dr Mike
PS — Comment CARDIO and I will DM you the Progressive 6 Protocol (P6P).
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The term 'CO2 tolerance' might be misleading. It's likely a desensitization to respiratory sensations, not a change in CO2 levels. Even leading researchers are unsure of the term's validity.
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Fitness advice often obsesses over mechanisms, not outcomes. Citing how a supplement *might* work (like creatine causing 'futile cycling' for fat loss) is cool, but lacks human data.
Don't assume a cool mechanism guarantees real results.
Just published: "Creatine As A Fat Burner? Easy There, Lab Coat Cowboy". Check it out and subscribe to get everything I'm making.
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