Picture this, you are sitting in a homemade freezer filled with 41F water, cortisol spiking, teeth clattering like a broken jackhammer, and you're proud of yourself.

Ok, so that was me before hitting the warm realms of South Padre.

Truth be told, I have been subjecting myself to cold water immersion of various degrees when I am home for over 6 years now.

Why you ask?

Hang on and I will answer that, but first, here is what is actually happening inside your muscles that you just trained if you hop into the cold abyss right after training.

Microvascular blood flow drops ~68% the moment you submerge.

Not a little. 68% home fry .

And it doesn't come back for up to 3 hours.

Now ask yourself: what travels through blood?

Amino acids Bro!

Every anabolic signal your body just cranked up during that session.

You trained.

You created the stimulus.

Your body said "yes, let's build" — and then you turned off the supply line like someone stepping on your air line when doing snuba on your cheap Margaritaville at Sea cruise adventure.

Data from tracer studies (this is where it gets ugly) put specific numbers on the damage.

Fuchs et al. (2019) watched dietary phenylalanine incorporation into myofibrillar protein in real time.

Cold leg vs. warm leg. Same person. Same workout. Same meal.

The cold leg showed ~26% less dietary amino acid incorporation into new muscle tissue over 5 hours.

Betz et al. (2025) then measured the correlation between that blood flow crash and the amino acid delivery impairment: r = 0.65.

That's not a rounding error. That's a mechanism.

And it compounds.

Run post-lift ice baths every session for 2 weeks — as Fuchs did — and your daily myofibrillar fractional synthetic rate (the actual rate your body is building muscle, day over day) drops ~12%.

Not acutely. Every. Single. Day.

Seven weeks of this?

Twelve weeks?

The MRI and biopsy data from Roberts et al. and Fyfe et al. show exactly what you'd expect: measurably less quad mass.

Blunted Type II fiber growth.

Suppressed mTOR signaling.

Satellite cell activity in the crapper.

Your strength? Largely preserved, interestingly.

But size? You left it on the floor of the ice tub.

What The GooRoos Got Wrong

Every bro-science take says cold blunts inflammation, and inflammation was your gainZ you crazy meat stick.

However if GooRoo Roy17 would actually read any full study on cold water immersion and not just ask AI for its interpretation, they would be shocked (Nelson, 2026).

Inflammatory markers — IL-6, TNF-α — are all over the place between CWI and active recovery groups.

The meta-analytic data (Piñero et al., 2024) only finds C-reactive protein reliably elevated with CWI — and that's a different pathway entirely from acute hypertrophic signaling.

In non-geek speak? Cold water immersion does NOT blunt inflammation.

Cold → vasoconstriction → nutrient delivery collapses → MPS tanks.

It's a plumbing problem, not a chemistry problem.

But hold there BroBigBicep88 before you throw out your chest freezer:

I'm still a fan of ice baths.

Strategically deployed, they're a legitimate tool — pre-competition, acute soreness management, situations where getting hyooooge at all costs is not the goal.

The question is: are you using the tool, or is the tool using you?

Since you are a loyal reader here of this amazing newsletter, you are in luck my hypertrophy seeking friend.

I wrote the full breakdown — protocols, temperatures, durations, the mechanistic cascade, the open questions the research hasn't answered yet, and exactly when CWI helps vs. hurts — and I'm giving it to you at no cost.

​ >> Download: Ice Baths & Muscle GainZ​

Read it.

Argue with it.

Send it to the guy in your gym who ice baths after every single session like it's a religion.

...and the main reason I still use cold water immersion is that I want to challenge myself daily with a hard task. Plus I keep the duration short and do it typically post cardio and rarely after lifting.

Much love and warm microvascular perfusion,

Dr. Mike

PS- Page 7 of the PDF has a detail almost nobody in the cold exposure world is talking about: we have zero human data on whether delaying your ice bath by even 3–6 hours post-lift changes the outcome. Zero. That gap in the literature hints at something bigger — cold as a deliberate training stressor with precise timing, not a blunt recovery hammer.

​ >> Download: Ice Baths & Muscle GainZ​

PPS- Temperature is one of four physiological flexibility pillars I'm opening up in full on April 20th. More on that soon. For now — grab the PDF and see if you can spot where the real leverage is.

References

Betz, M. W., Fuchs, C. J., Chedd, F., Monsegue, A., Hendriks, F. K., van Kranenburg, J., Goessens, J., Houben, A., Verdijk, L. B., van Loon, L. J. C., & Snijders, T. (2025). Postexercise cooling lowers skeletal muscle microvascular perfusion and blunts amino acid incorporation into muscle tissue in active young adults. Medicine & Science in Sports & Exercise, 57, 1866–1876.

Fuchs, C. J., Kouw, I. W. K., Churchward-Venne, T. A., Smeets, J. S. J., Senden, J. M., van Marken Lichtenbelt, W. D., Verdijk, L. B., & van Loon, L. J. C. (2019). Postexercise cooling impairs muscle protein synthesis rates in recreational athletes. The Journal of Physiology, 598(4), 755–772.

Fyfe, J. J., Broatch, J. R., Trewin, A. J., Hanson, E. D., Argus, C. K., Garnham, A. P., Halson, S. L., Polman, R. C. J., Bishop, D. J., & Petersen, A. C. (2019). Cold water immersion attenuates anabolic signalling and skeletal muscle fiber hypertrophy, but not strength gain, following whole-body resistance training. Journal of Applied Physiology, 127(5), 1403–1418.

Nelson, 2026 - yep, I actually put this into AI and it said quote "Yes, cold water immersion blunts inflammation" Which is wrong.

Piñero, A., Burke, R., Augustin, F., Mohan, A. E., DeJesus, K., Sapuppo, M., Weisenthal, M., Coleman, M., Androulakis-Korakakis, P., Grgic, J., Swinton, P. A., & Schoenfeld, B. J. (2024). Throwing cold water on muscle growth: A systematic review with meta-analysis of the effects of postexercise cold water immersion on resistance training-induced hypertrophy. European Journal of Sport Science, 24(2), 177–189.

Roberts, L. A., Raastad, T., Markworth, J. F., Figueiredo, V. C., Egner, I. M., Shield, A., Cameron-Smith, D., Coombes, J. S., & Peake, J. M. (2015). Post-exercise cold water immersion attenuates acute anabolic signalling and long-term adaptations in muscle to strength training. The Journal of Physiology, 593(18), 4285–4301.

____________________

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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