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Mutzel & Seager Talk Ice Bath Science

Updated: Feb 12

How does cold plunge boost testosterone, modulate metabolism, relieve stress, and why is it essential for human well-being?


  • Myoxcience Founder Mike Mutzel recently hosted Morozko Forge co-Founder Thomas P Seager, PhD on his High Intensity Health podcast. The text below is a summary of their conversation, with links to articles that provide more detail about the science and experience of ice baths, including:

    • Stress management,

    • Optimization of metabolism,

    • Risks, contraindications, and precautionary protocols,

    • Testosterone restoration, in men & women,

    • Ancestral origins of cold water immersion,

    • Why ice baths are unlikely to help you lose weight,

    • How to stack ice baths, exercise, and sauna for maximum benefits,

    • Brain and memory boosting effects, and

    • What differentiates Morozko from competitors.

High Intensity Healthy: Science & Experience of Ice Baths

Deliberate cold exposure for stress management

The concept of stress didn't exist until the mid-20th century. It had to be invented by a doctor and endocrinologist named Hans Selye (1907-1982). Born in Austria, during his medical studies Selye noticed that different disease states were characterized by a common set of symptoms, including inflammation, elevated cortisol, lethargy, and loss of appetite. Selye wondered how specific diseases could all share the same non-specific characteristics (Tan & Yip 2018). Selye hypothesized that the body is prepared by a general set of protective responses to wide variety of threats or exposures, and he called these stress.

During a lifetime of prolific scientific investigation of the body's response to stress, Selye discovered that stress is not necessarily a bad thing for health. Some stress, he realized, was essential to maintaining robust endocrine, metabolic, and psychological capacities. Finally, he argued that the meaning we choose about our stress is critical to determining the health outcome resulting from it. A constructive approach to stress, he reasoned, was essential to achieving a rewarding lifestyle.

Complete freedom from stress is death. - Hans Selye (1974, Stress Without Distress, p20).

Cold exposure was one of Selye's favorite generalized stress stimuli for studying physiological responses of stress. Working with rats and other animals, Selye documented how the hypothalamus, pituitary, adrenal glands and immune system adapted to stress.

Later, psychologists and psychiatrists adapted cold stress testing to assess their patient responses. Presumably, those patients who better tolerate the cold pressor test, in which they submerge their non-dominant hand into a bowl of ice water for up to five minutes, are better equipped to adapt to the daily frustrations, inconveniences, and discomforts of life.

What they've discovered is that stress itself is not dangerous to human well-being -- it is our beliefs about stress that dictate our health response. For example, Stanford Psychologist Kelly McGonigal summarized research that showed those people who experienced stress, but believed that the stress was beneficial for them lived longer than those people who reported feeling little or no stress (McGonigal 2012, The Upside of Stress).

Because an ice bath practices stimulates the body's stress response, it provides a training ground for stress management. In Ice Bath vs Cold Plunge for Heart Rate Variability, I described how the lower temperatures of the ice bath ensure activation of the fight-or-flight response in the sympathetic nervous system. However, structuring the breath strengthens the parasympathetic nervous system that is responsible of calming the body back down. According to Dr. Jay Wiles, Chief Science Officer at Hanu Health, the end result can be an improvement in the single best physiological measure of psychological resilience -- heart rate variability (HRV).


The processing of food for the energy necessary to power growth, exercise, thought, recovery, wound healing, and every other function of the living human body is called metabolism. Given that metabolism is the essential function that supports life, is it any wonder that every leading cause of death from chronic illness in the United States originates in a disorder of metabolism called insulin resistance? (Bikman 2020, Why We Get Sick).

What gets overlooked too often is the essential role that brown fat plays in the modulation of metabolism. Whereas white fat is for energy storage, brown fat is primarily for converting glucose and fat energy into heat to defend core body temperature against the cold. When thermoreceptors in the skin sense cold temperatures, they signal the hypothalamus to activate brown fat to perform what's called non-shivering cold thermogenesis. For example, human babies have copious quantities of brown fat to keep them warm during winter. However, as I wrote in How To Increase Brown Fat, without regular cold exposure to keep it active, brown fat disappears from the human body. By middle-age, fewer than 5% of American adults have any detectable brown fat at all.

That's a problem, because brown fat is not just for thermogenesis. It is also an essential secretory organ, which is to say that it produces hormones and neuroprotective factors that guard the brain. Among the most important of these is thyroid hormone.

The thyroid and brown fat are in constant biochemical communication to regulate metabolism. In fact, active brown fat produces more thyroid hormone than the thyroid does. Without the brown fat maintained by cold exposure, the thyroid can become dysregulated, such that hypo- or hyperthyroidism can result. When a regular practice of cold exposure restores brown fat, thyroid function will sometimes return to normal. (See The Cold Connection to Hashimoto's for examples).

Moreover, increased levels of brown fat are associated with improved insulin sensitivity -- i.e., the opposite of insulin resistance. In Deliberate Cold Exposure for Diabetes, I summarized studies of men with Type 2 diabetes experience such an improvement in their blood glucose readings after only ten days of cold exposure, that many of them no longer met the diagnostic criteria for diabetes. Those findings have been consistent with the experiences of cold plungers who have sent me their continuous glucose monitoring data showing improved blood glucose readings for hours after their ice bath. However, what's really interesting about the study is that the men didn't report shivering or being very uncomfortable -- partly because they were being exposed to 60F air instead of 34F water.

The metabolic benefits of cold exposure can be realized at higher temperatures than the psychological benefits. Only temperatures that are cold enough to frighten you will likely improve heart rate variability.

Contraindications and dangers in deliberate cold exposure

The number reason to avoid the ice bath is not wanting to do an ice bath. That is, it's important that everyone enter the ice bath of their own volition -- without coercion, and without bullying. However, there are also some medical contraindications that I wrote about in Contraindications to Cold Exposure and some precautionary protocols that I summarized in The Dangers of Deliberate Cold Exposure (Ice Bath Safety).

Medical contraindications can be categorized as cardiovascular, neurological, cold-related diseases, and adverse drug interactions. The most important of these is related to Ice Baths Hypertension & Hormesis (high blood pressure). In Are You Getting Enough Vasoconstriction? I described the phenomenon by which smooth muscles surrounding blood vessel will constrict the blood flow to limbs and extremities during cold exposure, to defend core body temperature. The result is an increase in blood volume in the core, and a temporary increase in blood pressure. For those already suffering from hypertension that temporary increase may be dangerous, even though the hormetic effects of vasoconstriction will ultimately result in improved blood flow and may lower blood pressure over the long term.

Among the neurological contraindications, the most important of these is Raynaud's Syndrome, in which a complex interaction of physiological and psychological factors cause an extreme, painful vasoconstriction that exceeds a normal, healthy adaptive response to ordinary cold stimulus. In primary Raynaud's, in which the syndrome exists independent of other diseases, exposure therapy to the cold may resolve the Raynaud's. Both Mike Mutzel and I have experience with Raynaud's suffers who have overcome their symptoms by using cold water immersion therapy under the supervision of a knowledge guide.

The precautionary protocols for ice bath safety relate to drowning, autonomic conflict, hypothermia, and operating during rewarm.

  • To avoid drowning, always plunge sober and never combine hyperventilation with cold exposure. Either could result in shallow water blackout, in which the body loses consciousness before it feels the urge to breath.

  • To avoid autonomic conflict that could interrupt healthy function on the heart, enter the ice bath feet first and maintain structured breathing during your plunge. Do not hold your breath during your cold exposure. Even if performing a head dunk, you can breathe via slow exhale, blowing bubbles underwater while your nostrils are submerged.

  • Hypothermia is very rare when practices ice baths. It takes more than 30 minutes of whole-body cold water immersion to drop core body temperature several degrees Celsius. To avoid hypothermia Don't Cold Overdose, and have access to safe rewarming protocols if you find that you accidentally do get too much cold.

  • Speaking of rewarming, it is essential to give your brain and body time to restore proper circulation before you drive your car, or do anything that requires full mental function.

How to Use Ice Baths to Restore Testosterone

One of the most important findings regarding my ice bath research was discovered entirely by accident. As I wrote in What Happened to My Testosterone... I was doing a combination of ice baths and ketosis to reduce a blood marker of prostate inflammation called Prostate Specific Antigen (PSA). Because I was cold after my ice bath, I rewarmed by body with light exercises. My favorite is steel mace flow, like Leo Savage taught me.

Because I was tracking a complete male health panel of labs to monitor my PSA, I also got readings on my total and free testosterone. I was glad to see my PSa drop from over 7 to less than 1 ng/mL, and I was surprised to see my total testosterone jump to over 1100 ng/dL -- which is considered abnormally high for a man in his 50's. My urologist insisted that I test my Luteinizing Hormone, to see if my gonads were making all that testosterone naturally, or if I were taking some kind of supplement. So i went back to the lab, and sure enough my luteinizing hormone was off the charts, too.

Since then, I discovered that there is a body of scientific literature suggesting that doing cold stimulation before exercise will boost testosterone in men, while doing cold after exercise will lower testosterone. I wrote a new article about it called How to Use Cold Plunge Therapy to Boost Testosterone, Naturally that describes the effects on both men and women. There is only one study that enrolled both sexes, but it showed that the results for women are likely different than they are for men. Using the cold pressor test, researchers measured an increase in the saliva testosterone in young women after cold stimulation even without exercise, whereas the same measurements in men showed a drop. These findings suggest that when training for anabolic gains, men should be precooling their exercise by doing their ice baths before their workout.

Use exercise to recover from the cold, not the other way around.

What's more, studies of precooling show a major boost to athletic performance as a result of pre- and percooling. In Precool Your Workout I described the studies conducted at Stanford University by Craig Heller, PhD that showed massive increases in peak muscle power output and endurance as a result of cooling the palms during strenuous exercise. What's really surprising is that separate research also shows that Precooling Speeds Exercise Recovery. That means that if you're going to use an ice bath to reduce the muscle soreness that follows a difficult workout, you should still probably be doing your ice bath before your exercise.

The ancestral necessity of cold exposure

Common sense demands a question with regard to the health benefits of cold exposure, and the question goes something like this:

If my ancestors are from warm, tropical climates, why would I need cold exposure to be healthy?

The answer is found in the equatorial glaciers of East Africa, where the oldest known human fossils have been found. Because mountains like Kilamanjaro rise so high in elevation, they are topped by permanent glaciers, despite the fact that they lie on the Equator. During the Ice Ages, these glaciers were much larger than they are now, and must've pushed the few thousand Homo Sapiens from which we are all descended into narrow stretches of land that existed between the edge of the ice and the cold ocean.

As I wrote in How Cold Water Shaped Human Evolution, those early humans survived in the water. They dove in it, foraged for food in it, and birthed their babies in it. The aquatic nature of the earliest human beings explains several anatomical features that make human more like other aquatic mammals than like strictly terrestrial primates. For example, human nostrils point down instead of out, so we don't get water forced up into our nose when we dive. And compared to chimpanzees, gorillas, and bonobos, human hands are webbed between the fingers, for better paddling. Water is probably we human beings walk upright, instead of on all fours, so that we can hold our heads above the water line while wading. And there is no doubt that the human brain could not have evolved to such a large size without the benefit of omega-3 fatty acids from shellfish and other foods found in the water. But the most amazing thing about humankind that suggests we evolved for cold water immersion is that human babies are born with an instinct to swim.

No matter where our near ancestors came from, our ancient ancestors lived both in at at the water's edge, or they never would have survived the Ice Ages. And given the geography of the evolutionary Garden of Eden in which humans emerged, the waters that fostered our evolution must've been cold.

Do ice baths help you lose weight?

Because it is true that cold water immersion will boost the metabolism, clear glucose from the bloodstream, and burn fat for hours, it's sensible to suggest that all the calories burned by an ice bath must contribute to weight loss, right?

Not so fast.

As I wrote in Calories and Cold Exposure, compensatory metabolic mechanisms at night likely make up for the deficit of calories created by cold exposure during the day. That is, body temperature tends to drop a few degrees the night after a day of cold exposure, dropping the metabolic rate in a way that may help with sleep quality, but fail to promote weight loss.

What cold water will do is remodel body fat from unhealthy patterns of visceral (belly) fat to more healthy patterns of subcutaneous fat. Whereas visceral fat is associated with heart disease and increased mortality, subcutaneous fat is typically more benign. Moreover, a regular practice of cold water immersion will reduce liver fat, which promotes healthy liver function and longer life.

Stacking ice, exercise, and sauna?

Mutzel is a big advocate of using sauna for promoting cardiovascular health, and has found some research suggesting that doing sauna after exercise is especially beneficial.

Mutzel cites the Finnish scientists, whom I've found are typically working at the leading edge of thermal contrast therapy, who discovered that sauna confers many of the same benefits as exercise.

Mutzel says, "Sauna is an exercise mimetic. That is, it mimics many of the same benefits of exercise," including improvements in VO2 max.

Given that cold water immersion, sauna, and exercise all have complementary and similar benefits, but the order in which you do them is important, then it's reasonable to ask what sort of exercise + thermal contrast stack will get the most out of each?

In Ice Bath, Exercise, Sauna Protocol... I suggested that you do the ice bath first, then the exercise, and then the sauna. There has never been a study of this particular protocol that demonstrates whether the individual benefits of each can be maximized by stacking them in this order. This protocol is a hypothesis based on aggregation of other studies that have examined them separately.

Nonetheless, a cold->exercise->heat regimen might make sense from an evolutionary perspective. Consider a hypothetical day of waking, foraging for fish or shellfish in the cold water, emerging with the day's catch, walking back to a camp, gather firewood, making a fire, and cooking the meal. To what protocol would our ancient grandparents have been been expected to adapt?

Cold, exercise, then heat of the fire.

Ice bath for brain health

Whole-body cold water immersion has a long-standing history as therapeutic hypothermia for promoting brain health, although the mechanisms are only just starting to come to light. For example, we now know brown fat will secretes FGF-21, a neuroprotective factor that guards against brain damage. In Cognition & Cold Exposure, I wrote about how activation of brown fat by cold water immersion will protect the brain against markers of Alzheimer's dementia and boost the metabolism that promotes better mood and cognition. Similarly, Brown Fat for Brain Health describes the way that insulin resistance contributes to cognitive decline, and how cold exposure can remedy that decline and extend the healthspan of our brains.

Professor Joe Dituri of the University of S Florida has measured his brain activity while in the ice bath, and finds an enormous improvement in frequencies characteristic of focused attention (compared to measurements taken when warm and dry). Dituri specializes in healing traumatic brain injury (TBI) -- partly because he himself suffered a TBI as a result of a car wreck. His ice bath practice is part of the protocol he designed to restore his own brain to good function. I wrote about Dituri in Ice Bath Boosts the Brain.

Finally, I heard from one avid ice bather who swears that his habit of plunging after a rehearsal improves his memory. Big Brev is an opera singer, who is required to memorize the score, the lyrics, the translation, and stage directions to execute a flawless performance. He discovered that the cold activation of his central nervous system immediately after his rehearsals reduces the amount practice time he needs to complete his memorization. I explained the evolutionary rationale that might account for this in Ice Bath for Better Memory.

To shiver, or no?

Some researchers may encourage you to not shiver while cold plunging. Their reasoning may be that suppressing your shiver responses encourages your brown fat to work harder to warm you up. However, in Should I Shiver? I wrote about the nervous system benefits of shivering.

Trauma is not synonymous with stress. Trauma is a maladaptive response to stress.

One of the ways that the body releases stress from the central nervous system is by trembling, or shivering. In Ice Bath & Trauma I quoted Dr. Peter Levine's work on somatic embodiment of trauma, and his description of the way that movement is essential to resolving PTSD. In the absence of releasing the activation in the central nervous system through either fight or flight, shivering can be a therapeutic way to protect the body against unresolved emotions.

Which ice bath to buy?

There are three things that make Morozko different from imitators and competitors. Morozko is colder, cleaner, and safer. It accomplishes that as follows:

  • Morozko is the only ice bath made in the USA that makes ice. It is the coldest ice bath in the world.

  • The water treatment system in the Morozko uses ozone. It does not require chlorine, or added chemicals, or water changes. You treat the Morozko like you would a pool -- you vacuum it regularly, but you do not change the water in it, because Morozko uses the highest quality ozone generation technology available on the market. You can read about it in Ozone & Cold Water.

  • Finally, the Morozko is grounded -- not just the electrical wiring, but the water is grounded, too. That confers a number of benefits to the plunger, not the least of which is a reduction in blood viscosity and reduced risk of blood clots. Morozko is the only cold plunge equipment provider that is 3rd party verified as grounding the water, which you can read more about in Ice Bath Grounding and Your Ice Bath Should Give Your Grounding Therapy.

Note: When you're ready to order, you can use the promo codes HIH350 to save $350 off the retail price of the Morozko Ice Bath, or HIH500 on the Morozko Pro.


  • Bikman B. Why We Get Sick: The Hidden Epidemic at the Root of Most Chronic Disease―and How to Fight It. 2020

  • McGonigal K. The Upside of Stress: Why Stress Is Good for You, and How to Get Good at It. 2012.

  • Selye H. Stress Without Distress. 1974

  • Tan SY, Yip A. Hans Selye (1907-1982): Founder of the stress theory. Singapore Med J. 2018 Apr;59(4):170-171. doi: 10.11622/smedj.2018043.


About the Author

Thomas P Seager, PhD is an Associate Professor in the School of Sustainable Engineering at Arizona State University. Seager co-founded the Morozko Forge ice bath company and is an expert in the use of ice baths for building metabolic and psychological resilience.

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5 comentários

bangali russian
bangali russian
23 de out. de 2023

Yes I’ve been doing it since early summer but my cold showers are not quite super cold yet and here in new York the weather is finally shifting to cold out, I do delivery on my electric bike from 8am to 12pm so looks like I’ll be getting a few hours of cold exposure before sauna now.

i presume if the Japanese study only exposed the wrists, then my face even partially exposed to the winter chill for a few hours should be good.

and I also have not gotten a base testosterone number so nothing to compare to.


bangali russian
bangali russian
23 de out. de 2023

As a New Yorker for over 20 years, it get brutally freezing cold in the winter months, i assume just being outdoors for even 30 minute per day in the winters helps get that cold stimulus for the brown fat? Also I feel like more research needs to be done as to how much "exercise" one needs after cold exposure to get the testosterone benefit, cause you do your hammer swings, that one old guy just goes for a jog with some weights, what if you just give yourself a little rubdown to warm up, is that exercise too? Is just going for a walk exercise? like how much is enough?

Also while your hypothetical real life scenario for "Cold -> Exercise…

Membro desconhecido
23 de out. de 2023
Respondendo a

I don't know. If you try it, will you share your experience with us?

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