Remember when a hard training session cost you one day?

Now it wants three days, a nap, and partial custody of your hamstrings.

Two nasty interval sessions a week 10 years ago? No problem. These days, one session has you negotiating with the stairs like a hostage mediator.

Biohacker Bob says, “You’re getting older. Just back off.”

Peptide Pauly says he has an “age-reversal” vial in a suspicious cooler behind his van down by the river.

Both are missing a BIG chunk of physiology.

Aging doesn’t just lower your recovery ceiling. It can shrink your buffer zone.

What the heck is shrinking?

Your body doesn’t defend one magical number. It operates inside a workable range. That range can expand or contract in response to what you throw at it.

Davies (2016) called this adaptive homeostasis: the temporary expansion or contraction of the normal operating range in response to small, non-damaging stress signals.

Heat.

Cold.

Low oxygen.

Hard training.

A short fast.

Appropriately dosed stressors can drive adaptation—but the response depends on the stressor, the person, and their recovery.

Here’s the part that hits harder after 40.

Pomatto and Davies (2017) describe how that ability to expand the range tends to decline with age. The rubber band doesn’t just lose some snap. It gets shorter.

That doesn’t prove every stressor below reverses age-related changes. It gives us a useful framework for thinking about dose and recovery.

The session that once felt like a speed bump now arrives wearing steel-toed boots.

Yesterday’s 24-hour recovery suddenly sends you a 72-hour invoice.

But this is NOT the part where I tell you to buy a rocking chair, stop training and just wait for the reaper.

Hell no!

You can still make meaningful training adaptations well into your 80s. The starting point may be lower, and the dose matters more, but the adaptive machinery hasn’t magically been hauled off to the scrapyard.

Meanwhile, society (aka the people “out there”) go from heated house to heated car to climate-controlled gym, then wonder why their ability to handle stress is getting rusty.

The goal isn’t to win the suffering Olympics as I love my AC, but it is to give your system a reason to adapt—and enough recovery to do it again.

Why this matters more at 55 than 25

At 25, you could sometimes get away with garbage programming. At 55, recovery sends you an itemized bill with tax.

And I heard you: time is your biggest obstacle.

Good. Because the answer is NOT fifteen new biohacks, seventeen supplements, and a second full-time job called “recovery.”

It’s a handful of controlled stressors, intelligently dosed, across the four physiologic regulators: temperature, pH, fuel, and breathing.

More useful signals. Less junk fatigue. No need to bury yourself under volume you can’t recover from.

Do this today

Pick ONE controlled stressor. Dose it like a professional, not a martyr.

A few hard intervals? Stop while the output is still crisp.

A sauna session? Give the cardiovascular system a nudge, not an audition for a survival show.

Cold exposure? Challenging is fine. Turning yourself into a human popsicle is not the prize.

Get in. Get the signal. Get out. Recover. Repeat.

That is the idea behind eustress: enough stress to stimulate a response, without piling on so much distress that the next three training sessions end up in the dumpster.

And that’s exactly what the Physiologic Flexibility Certification teaches: how to choose and dose these stressors for the human in front of you—not the imaginary superhero in the spreadsheet.

You can also split the cert into a more manageable payment plan at checkout.

>> Phys Flex Certification <<

TWO DEADLINES. DO NOT MISS THESE.

TONIGHT — Friday, October 16, 11:59 PM Pacific: The 4.5-hour Ask Me Anything audio series bonus disappears.

MONDAY — October 19: Enrollment in the Phys Flex Cert closes. The cert does not reopen until 2027.

Scott Umberger nailed it:
​
​“You want actionable information, not opinions from a reality show or internet guru that hasn’t worked with a single real person.”

Much love and a wider buffer zone,

Dr Mike

PS — Getting older is inevitable. Letting your buffer zone shrink without putting up a fight? Not so fast. >> Phys Flex Certification <<

REFERENCES

Davies, K. J. A. (2016). Adaptive homeostasis. Molecular Aspects of Medicine, 49, 1–7.

Pomatto, L. C. D., & Davies, K. J. A. (2017). The role of declining adaptive homeostasis in ageing. The Journal of Physiology, 595(24), 7275–7309.

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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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