Hola from the wind starved and dare I say - moderate temperature Texas coastline where the wind smells like salt, sunscreen, and the slowly evaporating dreams of tourists who underestimated the Gulf.

South Padre Island. Again. Yes.

Before you say anything — I know. Third email from this sandbar. But hear me out: the kiteboarding here is criminal in the best possible way, and somewhere between a 23-foot air and a bone-rattling kite-slam that rearranged several of my vertebrae in exciting new configurations, I decided to sit down and answer every single deranged question you crazy bastards sent me after yesterdays cold water immersion email.​

You absolute beautiful nerds.

Let's rip through these like a Category 4 wind through a beach umbrella stand.

Q1: My YMCA just installed a "waterless" polar wave cold tank — dry air, not water. Is cold just cold regardless of delivery? Also they got red light therapy. What gives?

— Melissa Schmidt, Owner, MindSet Nutrition Coaching LLC

Melissa. Melissa. You work at a YMCA that just strapped in TWO recovery modalities simultaneously and you're out here doing actual due diligence instead of just filming a TikTok in front of the cryo tank with a thumbs up. I respect this enormously.

On dry cold: Here is the physics fact that will ruin every "cold is cold bro" conversation at your facility forever: water transfers heat approximately 25 times faster than air at the same temperature.

So when your members walk into the waterless polar wave tank and emerge 3 minutes later feeling like champions of the human race, they are experiencing a fundamentally different thermal insult than the one I described in yesterday's email.

Could the dry cold tank do the same thing?

Theoretically yes, if the exposure were long enough and cold enough to achieve the same vasoconstrictive effect.

Practically? The heat transfer math says almost certainly not at typical commercial "wellness" temperatures with a short dip. And yes I did do actual research in heat transfer for my MS in mechanical engineering as I created a thermal model of monkey heads getting zapped by a big microwave transmitter.

What your dry cold members are almost certainly still getting: the dopamine and catecholamine dump — the epinephrine and norepinephrine spike — that makes them feel like they could deadlift a Buick on the way out. That part seems to work regardless of delivery mechanism. The nervous system doesn't care how it got cold. It cares that it got cold.

Tell the "wellness coaches" on the floor this: cold right after lifting as a blanket recommendation is still a bad idea even in a dry tank, because we genuinely don't know the interference threshold.

If someone is there specifically for hypertrophy, separate the cold from the lifting. If they're there for the psychological hit and to feel like a Norse god before driving home — fine. Just don't conflate the two.

On red light therapy (photobiomodulation for the nerds in the back): Oh, now we're cooking with photons.

The mechanism is legitimately interesting: specific wavelengths — red (~630nm) and near-infrared (~850nm) — most likely do penetrate tissue deep enough to interact with cytochrome c oxidase inside your mitochondria.

This upregulates ATP production and dials back oxidative stress locally. It's not magic. It's not snake oil. It is, however, deeply dependent on consistent application to see meaningful results. I've been doing red light most days I am home for about 7 years now. If you can do it near daily, there is some effect over time. If not, a one off session won't do diddly dink.

My buddy Ari Whitten has gone absolutely nuclear levels of deep on this topic and I have a podcast with him dropping soon that will be worth your time. Stay tuned.

Q2: I get home from the gym and jump in for maybe 30 seconds max. Mostly for the adrenaline rush. Are you saying even THAT blunts my gains?— Will

Will. My guy. Great to hear from you.

The shortest time frame in the existing muscle protein synthesis blunting literature is 10 minutes of immersion.

That is the floor of the data we have. Your 30-second "oh god oh god oh god" plunge followed immediately by sprinting for a warm towel?

My educated guess — and I want to be clear this is a hypothesis not a clinical statement — is that a sub-2-minute cold hit doesn't achieve sufficient vasoconstrictive depth to meaningfully tank your microvascular perfusion the way a 10-15 minute post-lift soak demonstrably does.

What you are getting is the catecholamine rocket — dopamine, epinephrine, norepinephrine — all of which feel absolutely electric once you're out and explain why you keep doing it despite the screaming.

There's a full breakdown of exactly how long, how cold, and when — and for what specific goal — inside the Phys Flex Cert. Temperature is Pillar 1. We go deep. You're welcome in advance, haha.

Q3: What about a walk-in cryo chamber? -124°F but only 3 minutes, and water transfers heat faster than air... so is this different?

You wrote this question like you already knew the answer and just wanted someone to confirm it.

Correct instinct. Gold star. Go to the head of the class.

You are right: water conducts heat roughly 25x faster than air, which means a 3-minute blast in a -124°F (-87°C) nitrogen-cooled space pod — while deeply unpleasant in its own special way — is not delivering the same physiological gut-punch as equivalent-duration cold water immersion.

The MPS interference data I've been throwing at you is overwhelmingly a water story. The cryo chamber probably does not create the same vascular shutdown cascade.

Probably.

We don't have the clean head-to-head data in healthy exercising populations, and I refuse to let anyone pretend we do.

What the cryo literature does have is some legitimately interesting work in inflammatory pathologies.

Research retrieved from the ole PubMed looked at whole-body cryotherapy in patients with ankylosing spondylitis — a chronic inflammatory spinal condition that makes your morning feel like someone drove a forklift through your lumbar spine overnight.

WBC at -110°C significantly reduced clinical disease activity scores and dropped IL-8 (a proinflammatory cytokine) compared to exercise therapy alone, with a more pronounced improvement in the colder group (Straburzyńska-Lupa et al., 2018).

Genuinely cool finding- baw haha, I could not pass up a good pun.

Now — and this is the part where I need you to tattoo this on your forearm — that is a pathology population.

People with chronically dysregulated systemic inflammation caused by an autoimmune condition. That is not you, post-squat, in your gym's basement recovery suite.

The "cold reduces inflammation and therefore you should ice bath after every lifting session" crowd is doing exactly what the worst science communicators do: they find a real effect in a real population with a real problem and they torch-and-pitchfork it into a universal recommendation for healthy people who have normal, functional, necessary post-exercise inflammation.

Cryo probably gives you the same dopamine/catecholamine hit as CWI. May help with perceived soreness. Lower hypertrophy interference risk than water...

..But the "cryo chamber is an anti-inflammatory hack for athletes" pitch is pathology data dressed up in Zubaz pants. I personally don't buy it.

Q4: Keep me posted on CWI BEFORE workouts. My heart rate is ~20 BPM lower for the same output. And does cold water actually raise testosterone? --Jason M

Jason, you absolute unit. You sent me data. Unsolicited physiological self-experimentation. We are the same species and I love you for it.

On your endurance observation — this is not nothing as A sustained ~20 BPM reduction for the same workload is a meaningful aerobic efficiency signal.

That's your cardiovascular system doing less work to move the same oxygen around, which is what adaptation looks like.

The question is whether CWI helped cause that or whether it's coincidental to other training changes — and the honest answer is: possibly yes, indirectly.

Research retrieved from Stanley, Peake & Buchheit, 2013, in European Journal of Applied Physiology studied cyclists grinding through consecutive days of training with post-exercise CWI versus passive recovery. The CWI group maintained sprint power better across the training block. More relevantly for you: vagal HRV (the ln rMSSD measure — your parasympathetic recovery marker) was significantly elevated immediately post-CWI versus passive rest.

Your nervous system was recovering faster. And a nervous system that bounces back faster between sessions executes subsequent aerobic work at higher quality, which is where real aerobic adaptation compounds.

This is where the context of when you use CWI matters enormously.

The MPS interference data is overwhelmingly in resistance training + immediate post-lift immersion.

If you're using cold primarily post-cardio — which is how I use it myself — you're playing a different game with different stakes.

The interference concern is real but it is not a blanket death sentence for cold exposure.

Timing, training modality, and goal specificity all matter. I know in your case you did CWI before and there is basically zero really good data on it that I can find.

Keep tracking it. This is genuinely interesting n=1 data and I mean that without irony.

On testosterone: I went so far down this particular research rabbit hole that I briefly forgot what sunlight looks like once again as my vitamin D levels hit near rickets level.

Short answer: CWI does not reliably raise testosterone.

In fact, if anything, CWI tends to blunt the anabolic hormonal environment you just earned in the gym; however that is post training which has been studied the most so far.

Nerd smash alert.

Earp et al. (2019): resistance-trained men, 15°C water for 15 minutes post-lift. Result — reduced or delayed the normal testosterone rise versus passive recovery.

Sakamoto et al. (1991): localized cold stimulation produced a ~10% decreasein serum testosterone with a paradoxical LH rise — meaning the signaling chain was working but the testes were ignoring it like a teenager being asked to do dishes.

Recent systematic reviews from Piñero et al. (2024) and Cain et al. (2025) find zero robust human evidence of a testosterone increase from CWI.

There's one small study hinting at a 24-48 hour testosterone "rebound" under longer CWI conditions. It's not been replicated.

My own labs via Function Health came back with slightly elevated test levels recently.

Did CWI do that?

Absolutely no idea as to what since there are confounders everywhere. N=1 data with no controls is a fun story and terrible science, but still interesting.

Do I still plunge? Yes. Every time I'm home and not currently living on a sand dune.

..But not because of testosterone.

Mainly to do something hard and the dopamine spike when you crawl out of 41°F water is one of the most legitimately alive feelings available and just behind flying 23 feet in the air for over 100 feet under a kite.

The real question underneath all of this:

Are you using cold? Or is cold using you?

Temperature is Pillar 1 of physiological flexibility — the actual, documented capacity of your physiology to shift between metabolic states under stress, recover faster, and adapt with less friction. There are four pillars. I've mapped them, built the protocols, written the implementation guides, and filmed the whole thing.

The Phys Flex Cert opens April 20th for exactly one week.

If you've been winging your cold exposure, your heat exposure, or any of the other three pillars without a framework — this is the framework. One week. Then it closes.

Much love, cold water, and a healthy disrespect for nonsense,

Dr. Mike

PS— Temperature is just Pillar 1. The other three are things most coaches have never even framed as trainable capacities. April 20th it opens again

References

Cain, T., McGannon, K., & Malhotra, A. (2025). Effects of cold-water immersion on health and wellbeing: A systematic review. PLOS ONE, 20(7), e0317615.

Earp, J. E., Hatfield, D. L., Sherman, A., Lee, E. C., & Kraemer, W. J. (2019). Cold-water immersion blunts and delays increases in circulating testosterone and cytokines post-resistance exercise. European Journal of Applied Physiology, 119(8), 1901–1907.

Piñero, A., Burke, R., Augustin, F., et al. (2024). Throwing cold water on muscle growth: A systematic review with meta-analysis. European Journal of Sport Science, 24(2), 177–189.

Sakamoto, K., Wakabayashi, I., Yoshimoto, S., Masui, H., & Katsuno, S. (1991). Effects of physical exercise and cold stimulation on serum testosterone level in men. Japanese Journal of Hygiene, 46(2), 635–638.

Stanley, J., Peake, J. M., & Buchheit, M. (2013). Consecutive days of cold water immersion: effects on cycling performance and heart rate variability. European Journal of Applied Physiology, 113(2), 371–384.

Straburzyńska-Lupa, A., Kasprzak, M. P., Romanowski, M. W., et al. (2018). The effect of whole-body cryotherapy at different temperatures on proinflammatory cytokines, oxidative stress parameters, and disease activity in patients with ankylosing spondylitis. Oxidative Medicine and Cellular Longevity, 2018, 2157496.

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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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