Welcome to the Huberman Lab Podcast,

where we discuss science

and science-based tools for everyday life.

I’m Andrew Huberman,

and I’m a professor of neurobiology and ophthalmology

at Stanford School of Medicine.

Today, we are going to discuss the use

of deliberate cold exposure for health and performance.

Temperature is a powerful stimulus on our nervous system

and indeed on every organ and system of our body.

And cold in particular can be leveraged

to improve mental health, physical health, and performance,

meaning for endurance exercise,

for recovering from various forms of exercise,

for actually improving strength and power,

and for enhancing mental capacity.

In order to properly leverage deliberate cold exposure

for sake of mental health, physical health, and performance,

you have to understand how cold impacts the brain and body.

So today we are going to discuss that.

We’re going to talk about

some of the neural circuits and pathways,

some of the hormones involved.

I promise to make it all clear and accessible

regardless of whether or not

you have a scientific background or not.

We are also going to discuss very specific protocols

that you can apply,

which leverage variables like temperature, how cold,

how to deliver the cold,

for instance, whether or not you use a cold shower,

cold immersion, ice bath, circulating water, or still water,

whether or not you’re going for walks outside in a T-shirt

when it’s cold,

or whether or not you’re purposefully using things

like cryo, if you have access to that or not.

One thing I can promise you

is that by the end of today’s episode,

you will know a lot about the biology of thermal regulation.

That is how your brain and body regulates its temperature.

You will also have a lot of tools in your arsenal

that you can use and leverage

toward improving mental health, physical health,

reducing inflammation in the body,

improving athletic performance,

improving mental performance.

I promise to spell out all those protocols in detail

as I go along and to summarize them again at the end.

I’d like to make a point now

that I’m going to make several additional times

during today’s episode.

And that is that temperature is a very potent stimulus

for the brain and body.

That also means that it carries certain hazards

if it’s not done correctly.

Now, everyone shows up to the table,

meaning to protocols,

with a different background of health status.

And there’s simply no way that I can know

what your health status is.

So anytime you are going to take on a new protocol,

that means a behavioral protocol or a nutritional protocol

or a supplementation protocol,

you should absolutely consult a board-certified physician

before initiating that protocol.

I don’t just say this to protect us,

I also say this to protect you.

If you’d like to see our medical disclaimer,

you can go to our show notes.

It’s described there.

In fact, I encourage you to please do that.

And in general, when embarking on new protocols,

in particular, if they involve strong stimuli

like changing temperature

or placing yourself into unusual temperatures,

I would encourage you to progress gradually.

I would also encourage you to not look at gradual progression

as the kind of weak version of a protocol.

In fact, today I’m going to discuss

a really beautiful peer-reviewed study

that involved having people do deliberate cold exposure.

So they were immersing themselves into water

up to about their neck.

And the water was actually not that cold.

It was only about 60 degrees Fahrenheit,

which for most people is pretty tolerable.

So nowhere near the kinds of extreme temperatures

that one could use in other protocols.

And the interesting thing is,

despite that fairly modest cold temperature,

by simply extending the duration of time

that people were in that water,

they experienced enormous increases in neurochemicals

that ought to translate to improvements in focus and mood.

And indeed, that’s what’s been observed

in subsequent studies.

So again, please see our medical disclaimer

in our show notes.

Please proceed with caution always.

Please also understand that the most potent stimulus

isn’t always the one that you experience

as the most intense in the moment.

In fact, I would encourage you to find

the minimum threshold of stimulus

that will allow you to derive the maximum benefit

from each protocol.

And indeed, I will point out

what those thresholds ought to be today.

I’ll give you some simple formulas,

gauges or guides that you can use

in order to navigate this extremely interesting

and potent tool that we call deliberate cold exposure.

Before we talk about deliberate cold exposure

and its many powerful applications,

I’d like to highlight a study

that I find particularly interesting

and that I think you will find

particularly interesting and useful.

The title of this study is,

brief aerobic exercise immediately enhances

visual attentional control and perceptual speed,

testing the mediating role of feelings of energy.

Now, the reason I like this study is,

first of all, it’s a fairly large size sample group.

They looked at 101 students.

These were college age students,

and they had two groups.

One group did 15 minutes of jogging at moderate intensity.

So when they did measure percent heart rates, et cetera,

but this would be analogous to zone two cardio,

which I’ve discussed on this podcast before.

Zone two cardio is cardiovascular exercise

that places you at a level where you can hold a conversation

with a little bit of strain,

meaning that you can get the words out,

but every once in a while you have to catch your breath.

Whereas if you were to push any harder

by any mechanism going faster or on a steeper incline,

et cetera, that you would have a hard time

carrying out a conversation.

So zone two cardio is a common form

of describing that level of intensity

that they call moderate intensity.

So one group did 15 minutes of jogging

at moderate intensity,

which I’m translating to roughly zone two cardio.

The other group did 15 minutes of relaxation concentration

that is somewhat akin to mindfulness meditation.

And then they were analyzed for perceptual speed,

visual attentional control,

something called working memory,

which is your ability to keep certain batches

of information online.

Just imagine someone telling you their phone number

and you have to remember that sequence of numbers

in your head for some period of time.

And that’s working memory.

And it depends very heavily

on the so-called prefrontal cortical networks,

which are involved in planning and action.

And they also looked at people’s feelings of energy

and they measured that subjectively,

how energetic people felt.

Now, the major takeaways from the study

that I’d like to emphasize are that

the 15 minutes of jogging group experienced

elevated levels of energy for some period of time

after they ceased the exercise.

Whereas the group that did mindfulness meditation

actually reported feeling more calm

and having less overall energy.

Now that’s very subjective.

And indeed they used subjective measures to analyze energy.

But what gets interesting is when they looked at

performance on these various cognitive tasks.

And the two tasks that they use

were called the trail-making tests.

They have different versions of this,

version A, version B.

I don’t want to go into too much detail,

but version A essentially involves

having a page of numbers that are distributed

somewhat randomly.

So 1, 2, 3, 4, 5, 6, 7, 8, and so on,

but distributed randomly across the page.

And people have to use visual search

to circle those numbers in sequence.

So this involves visual attention.

It involves some motor skills,

involves a number of things that

certainly require energy and focus.

The second test was the trail-making test part B,

as I mentioned earlier.

And this involved also circling numbers in sequence,

but interspersed between those numbers were letters.

So rather than just having to circle off numbers

in sequence, they actually had to connect one,

then the letter A, then two, then the letter B, et cetera.

And remember, these are randomly distributed across a page.

The major takeaway from the study is that

the group that did the 15 minutes of moderate exercise

prior to these two tests showed significant decreases

in the amount of time required

to complete these tests accurately.

That is interesting and indeed surprising,

at least to me, because there have been many studies

looking at the effects of mindfulness meditation

on the ability to focus.

The key variable in the study turned out to be energy.

This feeling, subjectively measured feeling, I should say,

of having more energy and thereby the ability to focus,

especially in these high cognitive demand tasks.

Now, the takeaway from this study for all of us,

I think is pretty straightforward.

If you are going to sit down to do some work

that requires focus and working memory

and cognitive attention,

and especially if it’s some visual spatial control,

meaning you have to search for things on a page,

you have to organize things on a page,

so this would be writing, arithmetic,

basically cognitive work of any kind,

15 minutes of moderate exercise done prior to that work bout

could be very beneficial for you.

This does not mean that mindfulness meditation

would not be a benefit to you.

I wouldn’t want you to conclude that,

but if you had to choose between doing 15 minutes

of mindfulness meditation

and doing 15 minutes of moderate exercise

prior to a cognitive work bout,

I would say the 15 minutes of moderate exercise

would be more valuable,

at least based on the data in this paper.

In many previous podcasts,

I’ve talked about the powerful effects

of doing things like mindfulness meditation

and other forms of NSDR, non-sleep deep rest,

so these could be 20 minute naps

or just lying there quietly with your eyes closed

or yoga nidra or NSDR scripts are available on YouTube

and various other places free of cost of any kind.

You can just go to YouTube, put in NSDR,

non-sleep deep rest.

Those protocols have been shown to be very beneficial

for enhancing neuroplasticity,

the changes in the brain and body that encode

or shift the neural circuits

that allow for memory to change,

that allow for learning to occur after a learning bout.

What I’m referring to today in this particular study

is the use of moderate exercise

in order to increase one’s focus and attention

in order to trigger that neuroplasticity.

So the simple sequence here is get energetic and alert,

do that prior to the learning bout,

engage in the cognitive work or learning bout,

and then mindfulness meditation, NSDR and so forth

should follow.

And if you would like to access this paper

and like to look more at the details in the paper,

we’ll be sure to put a link in the show notes.

The first author is Legrand.

And again, the title of this paper is

brief aerobic exercise immediately enhances

visual attentional control and perceptual speed,

testing the mediating role of feelings of energy.

And I also just want to emphasize immediately,

I think most people out there are interested in tools

and protocols that work the first time

and that work every time.

And indeed, I think this protocol fits that bill.

Before we begin, I’d like to emphasize that this podcast

is separate from my teaching and research roles at Stanford.

It is however, part of my desire and effort

to bring zero cost to consumer information about science

and science related tools to the general public.

In keeping with that theme,

I’d like to thank the sponsors of today’s podcast.

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Okay, let’s talk about the use of cold

for health and performance.

I confess I love this topic

because it takes me back to my undergraduate years

when I worked in a laboratory studying cold physiology,

its effects on the brain and its effects on the body.

And over the years,

I’ve always kept track of the literature in this area.

And indeed, there have been some tremendous discoveries,

both in animal models, so in rodents like mice and rats,

but also in humans.

And today we’re going to talk about

both categories of studies,

and I’ll be careful to point out

when discoveries were made in animal models

and when they were made in humans.

A key point when thinking about the use of cold as a tool,

and the key point is that you have a baseline level

of temperature that is varying,

changing across the 24-hour cycle.

So any use of deliberate cold exposure

is going to be superimposed on that rhythm,

that circadian rhythm, meaning that 24-hour rhythm.

The basic contour of your circadian rhythm in temperature

is that approximately two hours

before the time you wake up

is your so-called temperature minimum.

So your temperature minimum is a time

within the 24-hour cycle

when your body temperature is at its lowest.

Okay, so if you normally wake up around 6 a.m.,

your temperature minimum is probably about 4 a.m.

If you normally wake up at about 7 a.m.,

your temperature minimum is probably about 5 a.m.

It’s not exactly two hours before your wake-up time,

it’s approximately two hours before your wake-up time.

Now, as you go from your temperature minimum

to the time in which you are going to awake,

your temperature is rising slightly.

And then at the point where you wake up,

your temperature starts to go up more sharply

and will continue to go up into the early

and sometimes even into the late afternoon.

And then sometime in the late afternoon and evening,

your temperature will start to decline.

And indeed, as you approach sleep,

your body temperature will drop

by anywhere from one to three degrees.

And in fact, that decrease in core body temperature

is important, if not essential,

for getting into and staying in deep sleep.

Okay, so temperature rises with waking,

that’s easy to remember.

It tends to continue to rise throughout the day.

And in the late afternoon and evening,

your temperature will start to go down

and the drop in temperature actually helps you access sleep.

That background, or what we call baseline,

circadian rhythm in core body temperature

is important to remember because it helps us frame

both the effects of deliberate cold exposure

and it helps us frame when you might want to use

deliberate cold exposure in order to access specific states.

It also points to times within the 24-hour cycle

when you might want to avoid using deliberate cold exposure

if your primary goal is to get to sleep.

Okay, so that’s the circadian rhythm in temperature.

Now, I just briefly want to touch on thermal regulation

at the level of the body and the brain.

And this will be very surprising to many of you.

Let’s do what’s called a Gedanken experiment,

which is a thought experiment.

Let’s say I send you out into the desert heat

for a jog or a run, and it’s very hot outside,

you know, 102 degrees or 103 degrees.

And you start to move, you start to sweat,

and of course your core body temperature goes up.

Now, then I offer you a cold towel,

maybe a really, really cold towel.

And this towel is saturated with water

so you could actually squeeze the water out of that

and cool your body off.

And our Gedanken experiment is for me to say,

okay, where are you going to place the towel?

How are you going to cool yourself off?

And I’m guessing that most of you would think

that the best way to cool yourself off

would be to drape that towel over your head,

maybe your neck, over your torso,

and that it would feel really, really good

and they would cool you off.

Well, that’s exactly the wrong approach

if you want to cool off.

And in fact, if you were to use that approach,

your body temperature would continue to increase even more.

Yes, even more than had you not placed that cold towel

on your head or your torso.

And here is why.

Thermal regulation, meaning your brain and body’s ability

to regulate your internal core temperature

is somewhat like a thermostat.

And that thermostat resides in your brain.

So if you think about the thermostat

in your home or apartment,

if it’s too warm in your home or apartment,

and you were to take a bag of ice

and to put it on that thermostat,

what would the thermostat do?

It would register the environment as artificially cool.

It would think that the environment

was actually much colder than it is.

And so as a consequence,

it would trigger a mechanism

to further increase the temperature in the room.

And you have such a thermostat as well.

It’s called the medial preoptic area of the hypothalamus.

The hypothalamus is a small region of brain tissue

about over the roof of your mouth

and a little bit in front of that.

So it’s basically right behind your nose

and over the roof of your mouth.

And it’s a collection of neurons.

Those neurons have a lot of different functions

that include things like the control of aggression,

the control of sex behavior,

the control of temperature regulation and so on.

The medial preoptic area has connections

with the rest of the brain

or areas within the brain, I should say.

And with many areas within the body,

it receives input from receptors in our skin

and inside our body that register temperature

and it acts as a thermostat.

So if the surface of your body is made cool,

your medial preoptic area will send signals

by way of hormones and by way of chemicals

that will serve to heat your body up.

So what this means is that if you want to cool down,

the last thing you want to do

is to bring a cold surface of any kind,

towel or splashing water,

to the majority of your body surface.

It might be very, very surprising to you.

And you might say, wait, if I want to cool down,

I should jump into a cold lake or something of that sort.

That’s a different thing altogether.

What I’ll tell you,

and we’ll get into this in more depth later,

is that if you really want to cool down

quickly and efficiently,

you should leverage particular portals,

meaning particular sites on your body

where heat can leave your body more readily

and where cooling can have a dramatic and fast impact

on your core body temperature.

It can even save your life if you’re going hyperthermic.

We’re going to talk more about the specific protocols

to reduce core body temperature for sake of performance

and avoiding hyperthermia later in the episode.

Hyperthermia, of course,

is a very, very dangerous situation

because while your body can drop in core temperature

somewhat and still be safe,

you can’t really increase your body temperature that much

before your brain starts to cook

and other organs start to cook.

And by cook, I mean the cells actually start to die.

So you have to be very, very careful with the use of heat.

Heat stroke is no joke.

People die from heat stroke all the time.

You really want to avoid that.

One way to avoid that

is to cool the appropriate surfaces of your body.

And the appropriate surfaces in this case

are the upper cheeks,

or I would say the upper half of the face,

the palms of your hands and the bottoms of your feet.

I’ve talked about this on the podcast before

and in the guest episode with Dr. Craig Heller,

my colleague in the biology department at Stanford.

But just very briefly, these surfaces,

the upper half of the face,

the palms of the hands and the bottoms of the feet

are what we call glabrous skin surfaces,

G-L-A-B-R-O-U-S, glabrous.

And those surfaces are unique in that just below them,

the vasculature is different than elsewhere in the body.

Normally the passage of blood goes from arteries

to capillaries to veins,

but just beneath the glabrous skin

on the bottoms of the feet,

the hands and the upper half of the face,

you have what are called arteriovenous asthmosis.

These are portals of blood

that go directly from arteries to veins.

And in doing so,

allow the body to dump heat more readily, more quickly.

So as it turns out that if you are to cool

the palms of the hands, the bottoms of the feet

and the upper half of the face,

you can more efficiently reduce core body temperature

for sake of offsetting hyperthermia

and for improving athletic performance

and maybe even cognitive performance.

So we will return to the specific protocols for doing that

later in the episode.

I’ll give you a lot of details about how to do that,

how to do that without the use of any fancy

or expensive technology.

There are some technologies

that are now commercially available.

For instance, the so-called cool mitt

that will allow you to do that with maximum efficiency,

but I’ll also give you some at-home methods to do this

either in the gym or on runs or for sake of cognitive work.

Okay.

So the two key themes again are understand

that baseline circadian rhythm in temperature

and understand that the best way to cool the body

is going to be by making sure that something cold

contacts the bottoms of your feet,

the palms of your hands and the upper half of the face.

Ideally all three,

if your goal is to lower core body temperature quickly.

And again, just cooling off the back of your neck

or the top of your head or your torso with a towel

is going to be the least efficient way

to lower core body temperature

and might even increase body temperature

under certain conditions.

Okay.

With those two points in mind,

we can start to think about directed

deliberate cold exposure protocols.

And there are a number of different reasons

to use deliberate cold exposure.

And I want to separate those out for you.

There are cold protocols that have been tested

in peer-reviewed studies

that are designed to improve mental performance.

They are designed to improve things like resilience

or your grittiness or your ability to move through challenge

or to regulate your mind and your internal state

under conditions of stress.

And we can define stress very specifically

as times when adrenaline also called epinephrine

and or norepinephrine also called noradrenaline

are elevated in your body.

Forgive me for the noradrenaline, norepinephrine,

adrenaline, epinephrine nomenclature.

I didn’t make that up.

It turns out that every once in a while scientists disagree.

Imagine that.

And you’ll get multiple scientists

naming the same molecule different things.

Okay.

Norepinephrine and adrenaline are the same thing.

I will use them interchangeably.

Norepinephrine and noradrenaline are the same thing.

I will use those terms interchangeably.

Noradrenaline and adrenaline are often co-released

in the brain and body.

So they work as kind of a pair

to increase our level of agitation,

our level of focus and our desire and our ability to move.

They are often co-released from different sites

in the brain and body with dopamine,

a molecule that is commonly misunderstood

as the molecule of pleasure,

but is actually the molecule of motivation,

reward and pursuit.

So dopamine, norepinephrine and noradrenaline

tend to be released together under certain conditions.

And today you will learn how deliberate cold exposure

can be used to cause increases in the release of several,

if not all of these in ways that can improve

your levels of attention and your mood.

But the key point is that your mental state is shifted

when you are exposed to certain forms of cold.

And many people use deliberate cold exposure

specifically to shift their body state

as a way to train their mental state

so that they can better cope with stress in real life.

And by real life,

I mean when life presents stressful events.

And I will give you specific protocols

as to how you can do that.

In other words, how you can become more resilient

through the use of deliberate cold exposure.

Now, because of the ways in which deliberate cold exposure

can increase this category of chemicals

called the catecholamines,

that includes dopamine, norepinephrine and epinephrine,

it can also be used to elevate mood

for long periods of time.

And I’m going to discuss a specific protocol

that has been shown to increase these chemicals

anywhere from 2.5X, so 250%,

to as high as 500%, five times over baseline.

Now you might be asking whether or not it is a good thing

to raise chemicals like norepinephrine and dopamine

to such a great degree,

whether or not that’s healthy for us,

whether or not they can harm us.

But it turns out that these elevations

in norepinephrine and dopamine are very long lasting

in ways that people report feeling

vast improvements in mood

and vast improvements in levels of cognitive attention

and energy.

So by my read of the literature,

these seem to be healthy increases

in our baseline levels of these chemicals

in ways that can really support us.

So I’ll give you a protocol for that.

Now, those are some of the mental effects

of deliberate cold exposure,

but deliberate cold exposure has also been studied

in animal models and in humans

in the context of increasing metabolism,

even in converting certain fat cells

that we call white fat cells,

which are the ones where energy is stored,

the ones that we typically think of as kind of blubbery fat

to beige or brown fat, which is thermogenic fat,

meaning that it can increase core body temperature

and serves as kind of the furnace

by which we increase our core metabolism.

So with a very broad stroke,

I can say that white fat is generally the kind of fat

that people want less of,

and beige fat and brown fat is generally the kind of fat

that if you’re going to have fat cells

and you certainly need fat cells that you want more of,

they are thermogenic, they help you stay lean,

they actually serve as a reservoir for heating your body up

if you’re ever confronted with a cold challenge.

So we’re going to talk about how to use cold

for metabolism as well.

And of course, people are using deliberate cold exposure

to reduce inflammation post-exercise,

to reduce inflammation generally.

And people are also using cold to enhance performance

in the context of strength training,

in the context of endurance training,

and we’ll talk about those data as well.

But where I’d like to start is with mental performance,

and I’d like to detail what happens

when we deliberately expose ourselves to cold.

It’s key to point out the word deliberate.

If I don’t say otherwise, then throughout this episode,

if I say cold exposure, I mean deliberate cold exposure.

And the reason I point that out

is that as my colleague David Spiegel

in the Department of Psychiatry at Stanford says,

it’s not just about the state that we are in,

it’s about the state that we are in

and whether or not we had anything to do

with placing ourselves into that state

and whether or not we did that on purpose or not.

And what he really means by that statement

is that there are important effects of what we call mindset.

Mindset was a topic discussed in the guest episode

with Ali Crum some weeks ago.

If you haven’t seen that episode, I highly recommend it.

And the science of mindset tells us

that if we are doing something deliberately

and we believe that it’s going to be good for us,

it actually can lead to a different set

of physiological effects

than if something is happening to us

against our will or without our control.

Now, this is different than placebo effects.

Placebo effects are distinct from mindset effects.

If you want to learn more about the distinction,

please see the episode with Ali Crum.

But again, when I talk about cold exposure in this episode,

I’m talking about deliberate cold exposure,

meaning that you are placing yourself

into a cold environment on purpose

in order to extract a particular set of benefits.

When we talk about deliberate cold exposure,

almost always that means getting uncomfortable.

And one of the most common questions I get

when discussing the use of cold

for sake of mental or physical performance,

metabolism, et cetera, is how cold should it be?

How cold should the water be?

How cold should the environment be?

And I just will tell you now,

and I’m going to say this again and again

throughout the episode

because it will continue to be true throughout the episode

and long after the episode is over,

how cold depends on your cold tolerance,

your core metabolism, and a number of other features

that there is simply no way I could know or have access to.

So I would like you to use this rule of thumb.

If you are using deliberate cold exposure,

the environment that you place yourself into

should place your mind into a state of,

whoa, I would really like to get out of this environment,

but I can stay in safely.

Okay, now that might seem a little bit arbitrary,

but let’s say you were to get into a warm shower

and it would feel really, really nice.

And you were to start turning down the warm

and turning up the cold.

There would be some threshold

at which it would feel uncomfortable to you.

And if you were to continue

to make a little bit colder than that,

you would really want to get out of the shower,

but you were confident that you could stay in

without risking your health, right?

Without risking a heart attack.

Now that’s very different than jumping

into a very, very cold lake,

or I’ve seen these images of people that will cut holes

into frozen over lakes,

and they’ll get into that cold water.

If you are trained to do that

and you have the right conditions, et cetera,

that can be done reasonably safely,

but that’s certainly not what I would start with.

And for many people that will be too cold.

And indeed some people can go into cold shock

and can die as a consequence of getting

to that extremely cold water very quickly.

Now that’s not to scare you away

from deliberate cold exposure.

It’s just to say that there’s no simple prescriptive

of how cold to make the environment

in order to extract maximum benefit

for mental or physical performance.

So the simple rule of thumb is going to be,

place yourself into an environment

that is uncomfortably cold,

but that you can stay in safely.

Okay, and you’ll have to experiment a bit.

And that number,

meaning that temperature will vary from day to day.

It will vary across the 24-hour cycle

because of that endogenous,

meaning that internal rhythm in temperature

that I talked about earlier.

Low early in the day rises

into the afternoon drops at night.

You can actually do this experiment if you like.

Try getting into a cold shower at 11 o’clock at night,

if you want, versus try doing it

in the middle of the afternoon.

It’s quite a different experience.

And by quite a different experience,

I mean, it requires quite a different degree

of resilience and leaning into the practice.

Your willpower will have to be higher, I suspect,

late in the day as compared to early in the day.

But that will vary, of course,

between individuals as well.

So the most common question I get

about deliberate cold exposure

is how cold should the water be?

And we’ve answered that with uncomfortably cold

to the point where you want to get out,

but you can safely stay in.

The second most common question I get

about deliberate cold exposure

is whether or not cold showers are as good,

better, or worse than cold water immersion

up to the neck, for instance.

I also get a lot of questions

about whether or not cryo chambers

are better than all the others, et cetera, et cetera.

I’m going to make all of that very simple

for you by saying cold water immersion

up to the neck with your feet and hands submerged

also is going to be the most effective.

Second best would be cold shower.

Third best would be to go outside

with a minimum amount of clothing,

but of course, clothing that is culturally appropriate

and that would allow you to experience cold

to the point where you would almost want to shiver

or start shivering.

Now, there are a number of different important constraints

that are going to dictate whether or not

you use one form of cold exposure or the other.

For instance, some people don’t have access

to cold water immersion.

They don’t have access to ice baths or cold water tanks,

cold ocean or cold lakes, et cetera.

In that case, showers would be the next best solution.

I do want to emphasize that there have been very few,

if any, studies of cold showers.

And you can imagine why this would be the case.

In a laboratory, you want to control

for as many variables as possible.

So placing people into a cold water immersion

or an ice bath up to the neck

and insisting that they keep their hands and feet under

is very easy to control.

It means that everyone can do essentially the same thing,

whereas with cold showers,

people are different sized bodies.

Some people are going to put their head under.

Some people are going to lean forward.

Measuring the amount of cold water exposure on the body

is very hard to do.

And so there aren’t a lot of studies of cold showers,

but of course, a lot of people don’t have access

to cold water immersion, so they have to use cold showers.

And if you don’t have access to both, of course,

then going outside on a cold day can be of benefit.

But I will point out that the heat transfer

from your body into water is much higher,

four times greater, if not even greater,

depending on the temperature of the water,

in water as opposed to in air.

So it’s going to be much more efficient

to do cold water immersion than anything else.

Cold showers after that,

and put yourself into a cold environment

would be the third best thing.

I’m not going to get into cryo chambers

because they carry quite a high degree of cost.

And again, there aren’t many studies of them.

So if you have access to cryo chambers,

I’m sure that the cryo chamber facility

has told you about all these incredible benefits.

And I don’t doubt that some of those benefits truly exist,

but most people just don’t have the resources

or the access to those.

So we’re going to leave cryo chambers

out of today’s discussion.

And of course, I realized there’s a fourth category

of cold exposure out there.

People who are wearing ice vests,

believe it or not, those exist.

Ice underwear, yes, those exist.

You can look for them on Amazon if you like.

They are putting cold packs in their armpits

or in their groin or elsewhere

in order to stimulate some of the effects of cold

on mental and physical performance.

I’m not going to address those in too much detail today.

They can be efficient in certain ways,

but as you’ll learn about later in the episode,

cooling the palms, the upper face,

and the bottoms of the feet

is going to be far more efficient.

And unfortunately, I think most of the people

that are using ice packs to increase their core metabolism

are not aware of the glabber skin cooling

and how it can be a very, very potent stimulus.

So we’ll return to that later.

Unless I say otherwise,

I’m mainly going to be focusing on cold water immersion

and cold showers.

So let’s talk about protocols

for enhancing mental health and performance

using deliberate cold exposure.

What happens when we get into cold

is that we experience an increase in norepinephrine,

in noradrenaline release and in adrenaline release.

The fact that cold exposure, deliberate or no,

increases norepinephrine and epinephrine

in our brain and body

means that it is a very reliable stimulus

for increasing norepinephrine and epinephrine.

That’s sort of an obvious statement,

but that obvious statement can be leveraged

to systematically build up what we call resilience.

Now, when we experience a stressor in life,

whether or not it’s something bad happens

in our relationship or something bad happens in the world

and we feel stress,

that stress is the consequence of increases

in norepinephrine and epinephrine in our brain and body.

Very similar, if not identical,

to the kinds of increases

that come from deliberate cold exposure.

So deliberate cold exposure is an opportunity

to deliberately stress our body.

And yet, because it’s deliberate

and because we can take certain steps,

which I’ll describe in a moment,

we can learn to maintain mental clarity.

We can learn to maintain calm

while our body is in a state of stress.

And that can be immensely useful

when encountering stressors in other parts of life.

And that’s what we call resilience or grit,

our ability or mental toughness,

our ability to lean into challenge

or to tolerate challenge

while keeping our heads straight, so to speak.

So one simple protocol for increasing resilience

is to pick a temperature that’s uncomfortable

of shower or cold immersion,

and then to get in for a certain duration of time,

and then to get out.

Now, it’s important to understand

that people will experience different levels

of norepinephrine and adrenaline release

when getting into cold water.

Some people, because they dread the cold so much,

will actually experience norepinephrine

and epinephrine increases

even before they get into the cold water

or under the cold shower.

Now, you may have experienced this.

I’ve certainly experienced this.

I’m dreading it.

I don’t want to do it.

And I have to force myself to do it.

And indeed, epinephrine and norepinephrine

and its surges can be thought of as sort of walls

that we have to confront and go over.

And I’d like you to conceptualize them that way

because it allows us to build protocols

that can be very objective

and can allow us to monitor our progress

in terms of building resilience.

So one option is to simply say,

okay, I’m going to force myself

to get into the cold shower for one minute.

How cold?

Again, uncomfortably cold,

but you can stay in safely.

Or I’m going to get into the ice bath

for one minute.

Ice baths are very cold, inevitably.

And what is also inevitable

is that when you get into the cold,

you will experience a surge

in epinephrine and norepinephrine.

That’s non-negotiable

because it’s mediated by cold receptors

on the surface of your body and your skin.

And the way that they trigger the release

of norepinephrine and epinephrine,

not just from the adrenals,

from the adrenal glands above your kidneys,

but also from regions of your brain,

like the locus coeruleus,

which cause increases in attention and alertness,

and from other locations in your body

where epinephrine and norepinephrine are released.

In other words,

cold is a non-negotiable stimulus

for increasing epinephrine and norepinephrine.

Even if you are the toughest person in the world

and you love the cold,

that increase in epinephrine and norepinephrine

is going to happen.

So the way to think about norepinephrine and epinephrine

in this context of building mental resilience

is that you have two options.

You can either try to extend the duration

of time that you are in the deliberate cold exposure.

So going from one minute to 75 seconds,

to two minutes and so on over a period of days.

Or one way to approach this,

and the way that I particularly favor,

is to take the context of the day and the moment

into account.

Meaning we have different levels of grit and resilience

on different days,

and depending on the landscape of our life

at the time,

even the time of day that we’re doing these protocols,

and start to be able to sense

the release of epinephrine, excuse me,

and norepinephrine in our brain and body,

and see those as walls that we want to climb over

in order to build resilience,

and to start counting the number of walls that we traverse

and the distance between those walls

as we do deliberate cold exposure.

Let me give you an example of the timed protocol

because that one is very straightforward,

although I do not think it is as powerful

for building mental resilience.

The time protocol would be Monday,

I do one minute of deliberate cold exposure

at a given temperature.

Wednesday, I extend that by 50%.

And Friday, I do deliberate cold exposure

for twice as long as I did on Monday.

And if I were to continue that every week,

Monday, Wednesday, Friday,

I would continue to either increase the duration,

or I would lower the temperature and reduce the duration.

This kind of thing, very much like sets and reps in the gym.

Now that option is very objective, right?

You could even log it in a book.

And as you develop the ability to stay in cold temperatures,

even progressively colder and colder temperatures

for longer and longer periods of time,

you will become more resilient.

What do I mean by that?

Well, my operational definition of resilience

is that you are able to resist escape from the stressor,

the cold, by virtue of your willpower,

which is really your prefrontal cortex

causing top-down control on your reflexes

and your limbic system and your hypothalamus,

which are basically telling you

to get out of that cold water,

get out of that cold environment.

And in doing so,

you are basically getting better at controlling your behavior

when your brain and body are flooded

with norepinephrine and epinephrine.

That’s a very reductionist way to explain resilience

or greater mental toughness,

but it’s a reductionist way of explaining it

that is very closely tied to the biology

and to the psychology.

And it is a fact that norepinephrine and epinephrine release

in the brain and body

are the generic universal code for stressor.

There is no unique chemical signature

for different forms of stressors.

That is the only one.

Although, of course,

there are other chemicals involved as well.

So you could go for time

and you could try and reduce the temperature

and increase the time over a period of days or weeks.

Now that’s an attractive way to approach things,

but the problem is

that you don’t have an infinite amount of room

with which to lower temperature

because eventually you will get into temperatures

that are either so cold that they are dangerous

or you have to stay in cold temperatures

for such long periods that it becomes impractical

because presumably you also have to take care

of other aspects of your life.

You can’t just sit all day in the ice bath.

Now, for that reason,

I favor a protocol in which you build mental resilience

and mental toughness

through two different types of protocols.

The first one involves counting walls.

Now, what do I mean by walls?

I mean, the sensation of, no, I don’t want to do this,

and the idea or the sensation in your brain and body

that you actually want to leave that environment

and go warm up.

Now, again, for some people,

that will be even before getting

into the ice bath or cold shower.

So if you are feeling very resistant

to getting into the ice bath or cold shower

and you manage to do that,

that’s going over what I would call one wall, okay?

Then for some period of time,

you might actually feel comfortable

in the ice bath, cold water, or cold shower,

and you feel like you could stay there

for some period of time,

that you could stay there for a minute or two minutes,

but inevitably the next wall will arrive.

And I would encourage you to pay attention

to when that next wall arrives

and actually having an awareness,

that so-called interoceptive awareness, as we call it,

of when that next surge in adrenaline epinephrine comes

or whether or not it reaches a certain threshold

in your brain and body that you feel you want to get out,

and you’re able to stay in for even just 10 seconds longer,

that means you’ve traversed yet another wall.

And if you continue to stay in that cold environment,

you will find that the next wall will come

and the next wall will come.

Now, eventually, of course, you will get very, very numb,

depending on how cold it is,

and you could also place yourself into danger.

So you have to maintain cognitive control,

counting these walls, traversing these walls,

but getting out at some point, of course.

So my favorite protocol for building mental toughness,

aka grit, aka resilience,

is to take into account that some days

just getting into the ice bath or cold shower

represents a wall, some days it doesn’t.

Some days you get in

and you feel like you could go 10 minutes.

Other days you get in

and you feel like you could only go a minute.

And setting a designated number of walls

before you start the protocol

is going to be very beneficial here.

So you say, as long as I can do it safely,

I’m going to do three walls today.

The first wall is getting in,

the second wall will arrive when it arrives,

and the third wall will arrive when it arrives,

and I’ll get over that wall and then I’ll get out.

The next day, you might do five walls.

The next day, you might do three walls again,

but you might lower the temperature.

This gives you tremendous flexibility,

and indeed, it gives you much more latitude

to be able to use the same temperatures in different ways,

or to reduce the temperature only a little bit

and still get a lot of stimulus,

meaning a lot of results out of a given protocol.

Whereas people who are just going for temperature and time

eventually become cold adapted.

They get very, very good at doing three minutes

or six minutes or even 10 minutes at a given temperature.

And so then they feel like they have to lower

the temperature even more and even more,

and eventually they just bottom out.

There’s nowhere else to go.

There’s no way to get improvements out of the protocol,

at least not in terms of mental resilience.

Of course, there’s still the positive effects

on inflammation and metabolism, et cetera,

that we’ll talk about in a little bit.

But the key thing here is to design protocols

that are going to work for you over time.

And for you very, very hardy,

very, very tough guys and gals out there

that can get right into an ice bath

or a very, very cold immersion,

and you can just grind it out for six or 10 minutes,

or you can even do that by remaining peaceful.

Well, more points to you, but guess what?

That’s the equivalent of already having loaded up

the barbell with 600 pounds and done your 10 reps.

There’s not a whole lot more variable space

with which to get benefits from that stimulus.

And in the weight room, people understand

that you can adjust, for instance,

the speed of the movement,

or you can start combining that movement

with pre-exhaustion, et cetera.

With cold exposure,

you don’t have as much variable space to play with.

So if your goal is to build resilience,

either go for time as a function of temperature,

or what I suggest is to start recognizing these walls

as an experience of resistance in you

and going over those walls,

set a certain number of walls

that you’re going to go over on a given day

and do that at a given temperature,

and then to mix it up.

And ideally, you might even throw in one more wall

at the end if you’re really feeling bold and brave,

because that’s going to build out further resilience.

But if you want cold exposure to work for you

for sake of building up resilience

and mental toughness over time,

you’re going to want to vary this parameter space

in some sort of way.

And you don’t have to be super systematic about it.

That’s the beauty of this kind of approach,

because you’re relying on the fact

that those walls really represent times

in which you are forcing your top-down control,

your prefrontal cortex, to clamp down on your reflex,

and you’re learning behavioral control

in the context of your body having elevated levels

of these catecholamines, norepinephrine and epinephrine.

And that translates to real life

in a much more realistic way, I believe,

because in real life, you’re not really engaging

in stressors for a given amount of time

that you know how long it’s going to last

and you know the context.

No, most stressors arrive in the form

of surprises we don’t like,

text messages that deliver bad news,

information about the outside world or real world

and online interactions that send our system

into a state of increased norepinephrine and epinephrine.

And if you start to think of those as walls

that you can tolerate and climb over

while staying calm and clear of mind,

then you can really imagine how the ice bath

and other forms of cold exposure are really serving

to train you up for real life stressors.

Okay, the next question that I always get

is what should my mental state be

while I’m exposing myself to this uncomfortable

yet safe condition of cold?

Well, you have two options

and there are probably other options as well.

One is to try and calm yourself

to remain as mentally still as possible.

The other is to lean into that challenge

and so to grind it out.

And here, I have to say that this is a lot

like teaching someone to drive on a gravel road.

For any of you that have driven on a gravel road,

you know that there is no optimal speed

for all gravel roads.

It depends on the density of the gravel, et cetera,

and the vehicle, et cetera.

So for instance, on some gravel roads,

when you start to drive and the dust starts to kick up,

your best option is to drive fast

and put that dust cloud behind you.

On other gravel roads, if you try and do that,

the dust actually kicks up around the vehicle

and it makes it hard to see.

Sometimes you have to slow down.

The same thing is true

for getting through deliberate cold exposure.

Sometimes it’s easier to calm yourself.

One way to do that is through double inhales

through the nose and extended exhales through the mouth

or simply by trying to control your breathing

and reduce the pace of your breathing

and increase the volume of your breathing.

I have to say that everyone experiences

a shortening of breath

when they get into uncomfortably cold water.

That is a universal physiological response.

Everyone also experiences a 30 to 80% decrease

in cognitive function, in particular of the frontal cortex.

The metabolism of your frontal cortex goes down.

The metabolism, meaning the activity of brain areas

associated with stress and panic goes way up.

And so anchoring your mind in cognitive activities

as you get into the cold can be very, very helpful

for maintaining clarity of mind.

In fact, one thing that I sometimes recommend

is that people try and engage

in some sort of cognitive exercise while in the cold,

not as a form of distraction,

but as a way to maintain clarity of thinking

and to learn how to do that when the body is flooded

with all these chemicals that make us stressed.

So for instance, you could do math problems

and not two plus two equals four,

not three times three equals nine,

but things that require a little bit more focus

and attention, working memory and so forth.

You could also start to have thoughts

that you deliberately impose a full sentence structure on.

That’s actually quite tough.

You could try and recall specific bouts of information

that are challenging.

This is teaching your mind how to stay online,

or rather I should say,

this is you teaching your prefrontal cortex

how to stay engaged while you have high levels of stress

in your body.

Years ago, I had a friend who works

in the neuroscience world, research neuroscientists,

who was obsessed with this very bizarre sport

that I don’t necessarily recommend at all,

which is the combination of boxing and chess.

You may have seen this on YouTube

where people will box around, legitimate boxing around,

they’re sparring all out often.

And then at the end of the round,

instead of resting in the corner,

they actually sit down and play chess.

And then they go back to boxing and back to chess.

Again, not a sport that I recommend,

but the reason he was obsessed with this

is because he studies the impact of stress

on cognitive performance.

And what that particular very bizarre sport was doing

was toggling back and forth

between different states of mind.

Now it’s used both to increase cognitive clarity

for the fighter when they box,

because staying calm and clear thinking

is very important to winning boxing matches.

Believe it or not, it’s not an all outrage.

It’s a very calculated game of mental chess

and physical chess that’s quite high stakes,

as you can imagine.

It’s also used in some circles as a way to teach people

how to engage in cognitive performance

when their body is simply filled with stress.

So in the boxing chess example,

the replacement for the cold water

is actually the boxing, right?

It’s the thing that’s supposed to induce the stress

because getting hit is stressful

and the risk of getting hit is stressful for most people.

So again, if you think about deliberate cold exposure

as a way of just systematically

and reliably inducing epinephrine

and norepinephrine release and delivering stress,

well then this idea of maintaining cognitive clarity

and actually engaging in cognitive tasks

while in the ice bath or cold shower

can actually be very beneficial.

Even though it might sound a little bit silly,

you are really training up your ability

to keep your brain working when the reflex

is to shut down the parts of your brain

that are involved in deliberate planning and thinking.

Now, another important aspect of deliberate cold exposure

that I rarely, if ever here discussed,

but is vitally important

is whether or not you move around or not.

Here’s the reason.

When you get into cold water

and you remain there for some period of time,

your body is generating heat

and that heat generates what’s called a thermal layer

that surrounds your entire body.

So if you stay still,

you are actually warmer than if you move around.

You can try this the next time

you’re doing your deliberate cold exposure.

If you’re submerged up to the neck,

sit there for about 10, 30 seconds

and be very, very still of body.

In fact, this is the way that most people

start to do deliberate cold exposure.

They give this very stoic look.

They don’t blink.

They look very peaceful.

Some of them even look tough,

or they make a very even, a-emotional face.

And so it looks like they’re really tough,

but they are so still that believe it or not,

they are not providing the most potent stimulus.

If they or you were to move around in that water,

what would happen is you’d break up the thermal layer

and that you actually experienced that as much colder.

So if you really want to push the resilience aspect,

or for instance,

if you want to use a given temperature

that you’re comfortable in,

but that you want to increase the stimulus

and you want to get some more benefit

for mental resilience training,

well then get into the cold water,

move your body around continuously,

but try and keep your mind still

or even do some sort of cognitive task.

So as you’re starting to realize,

there are a bunch of different variables

that you can play with

while maintaining the same temperature of water.

And in doing so,

really keep you in the zone of what should

and absolutely has to be safe for you

without having to just continually drop the temperature

from say 60 degrees to 55 to 40 to 33,

because as I mentioned before,

eventually you’re going to bottom out.

So if you’re one of those people that likes to look tough

or really relaxed while you’re in the ice bath

or cold water immersion,

just realize that you’re actually cheating yourself

out of part of the stimulus.

Keep those limbs moving

and of course limbs under the water,

feet and hands is going to be a more potent stimulus

than hands and feet out

for reasons that should be obvious

based on what we talked about

in terms of glab or skin cooling.

So keep those submerged,

move your body, pedal,

maybe move your knees up and down, pedal your feet.

And trust me, it’s going to feel a lot colder

than were you to remain stone still.

Another very common question is how often

to do deliberate cold exposure.

It’s tough to make a recommendation on that

based on any peer reviewed study.

Although there are a few in humans

that point to a threshold of 11 minutes total per week.

So that’s total throughout the week

divided into two or four sessions

of two or three minutes or so.

Now that 11 minute cutoff is not a strict threshold

and is actually geared more towards increases in metabolism.

We’ll get into this a little bit later in the episode,

but I think the 11 minute threshold,

meaning 11 minutes total of deliberate cold exposure

per week is a pretty good number to use

if you need a number in order to keep you consistent.

But as we talked about earlier,

some of you are going to be in the ice bath

or cold immersion or cold shower for one minute.

Others of you will be in there for 10 minutes,

depending on how frequent and how high, if you will,

those walls of adrenaline are coming.

So for some of you getting into a cold shower

for three minutes total for the whole week

will represent a tremendous achievement

in terms of willpower and overcoming the resistance

to doing that, overcoming those walls.

For others of you, three minutes is nothing.

So what do I recommend?

I recommend that you get at least 11 minutes total per week,

but at the point where 11 minutes total per week

is very easy for you

or is no longer representing a significant mental challenge,

meaning you’re not experiencing many of these walls,

you’re excited to get into the cold shower or immersion,

you’re going through it easily, you’re cruising basically.

Then I would say either lower the temperature safely,

of course, extend the duration safely, of course,

or increase the frequency

so that you’re doing this perhaps every day

or maybe five days a week or three days a week.

I personally get tremendous benefit

from doing deliberate cold exposure three times a week

and using the walls method that I described earlier

as my gauge for how long to stay in.

And typically that means that I’m staying in

for anywhere from two minutes to six minutes per session.

And that averages out to about 11

to 15 minutes total per week.

So again, I do not think that you need to be super strict

about these guidelines.

It’s most important when embracing a protocol,

A, that you do it safely,

but secondarily that you do it consistently.

So find what you can do consistently

and then vary the parameters that will allow you

to continue to do deliberate cold exposure consistently,

regardless of whether or not you have access to a shower

or a cold immersion, et cetera.

Okay, so we’ve been talking about mental effects

and the use of deliberate cold exposure

for sake of building resilience,

which I do believe can be tremendously powerful.

Look, it’s no coincidence that the screening

and the training for Navy SEALs

involves a lot of exposure to cold water.

One could argue that it is deliberate

because they elect to go to BUDS,

but when they get into the cold water

at BUDS is dictated by the instructors.

And the reason they use cold water exposure as the stressor

is that it does offer considerable leeway

in terms of duration and temperature,

in terms of how you can use it as a stressor.

Whereas things like heat don’t offer much variable space,

as we say, there isn’t a lot of room

beyond which you start injuring

or even killing people by using heat.

So there are a lot of forms of stressors out there,

but cold is one that we can titrate,

that we can adjust in ways

that can allow us to continually build up

and or maintain mental toughness.

Now, deliberate cold exposure also has many effects

on chemicals other than norepinephrine and epinephrine,

most notably the neuromodulator dopamine,

which is involved in elevating our mood,

making us feel energized and enhancing our ability to focus.

And that has a lot to do with how dopamine engages us

in motivated states,

tends to narrow our thinking and our behavior

into a particular trench of goal-directed behavior.

If you want to learn more about dopamine,

you can learn a lot about dopamine

in our episode about dopamine, it’s at hubermanlab.com.

You can find it, it’s a two and a half hour

plus kind of deep dive into all things dopamine,

focus, motivation, et cetera.

Deliberate cold exposure has a very powerful effect

on the release of dopamine in our brain and body.

And this is one of the main reasons

why people continue to do deliberate cold exposure.

Basically, it makes us feel good

and it continues to make us feel good

even after we get out of the cold environment.

In fact, some people would say

they don’t feel good in the cold environment.

It’s all stress for them, but afterwards they feel great.

One of our previous guests, Dr. Anna Lembke,

who’s a medical doctor

at Stanford University School of Medicine,

she’s a close colleague of mine,

described the use of dopamine in her book,

Dopamine Nation, an incredible book

about addiction and dopamine, I should mention.

And the use of dopamine elicited by cold water exposure

by one of her patients.

What I’m referring to is the fact that one of her patients

helped themselves get and stay sober off drugs

by using deliberate cold exposure to increase dopamine.

So a healthier form of dopamine release

than they were engaged in prior to getting sober.

Now, the basis for dopamine release

in response to cold exposure

is that the catecholamines, norepinephrine, epinephrine,

and dopamine tend to be co-released

by the same sorts of stimuli.

But most stressors, and in particular things

that evoke stress or our feelings of stress internally

that we don’t like, do not increase dopamine.

They only increase norepinephrine and epinephrine.

But deliberate cold exposure

seems to cause a dramatic increase in dopamine.

And this has actually been substantiated

in a really beautiful study

entitled Human Physiological Responses

to Immersion into Water of Different Temperatures.

The first author is Sramek.

I’m almost certainly pronouncing that poorly,

if and if not incorrectly, S-R-A-M-E-K.

This was published in the European Journal

of Applied Physiology in the year 2000.

Really a beautiful study.

I love this study.

They took people and they had them sit in chairs

underwater, but their head was out

and so they were immersed up to the neck

in either of three different temperatures, excuse me,

32 degrees Celsius, which is 89 degrees Fahrenheit,

20 degrees Celsius, which is 68 degrees Fahrenheit,

or 14 degrees Celsius, which is 57.2 degrees Fahrenheit.

So not super cold.

But then what they did is they measured

people’s core body temperature throughout.

They measured their metabolism

and they looked at serum levels of things

like norepinephrine, epinephrine, dopamine, and cortisol,

serum meaning within the blood.

So a really nice and quite thorough study.

There were not a huge number of subjects in the study,

but nonetheless, it was a very thorough study

in terms of the number of variables that they explored.

So I just want to briefly highlight some of what they saw

or what they observed in this study.

First of all, all the groups were in the water

of a given temperature for one hour,

which is much longer than most

of the deliberate cold exposure protocols

that anyone is using at home.

I mean, maybe you’re taking one hour long cold showers.

Maybe you’re getting into the ice bath for an hour,

although I don’t recommend that.

I think you’d probably get badly hypothermic,

or maybe you’re getting into a cold water immersion

for some period of time,

but I have a hard time imagining that it would be an hour

and I don’t suggest that if it’s very cold.

So this study focused

on actually somewhat moderately cool temperatures,

not what I think most people would consider

very, very cold temperatures,

but extended the duration for quite a while.

So again, 32 degrees Celsius, 20 degrees Celsius,

or 14 degrees Celsius, here’s what they observed.

The group that was immersed up to the neck

in 32 degrees Celsius, that is 89 degrees Fahrenheit,

water did not experience a shift in metabolism

nor a significant increase in dopamine nor epinephrine

or these other catecholamines.

The group that was in 20 degrees Celsius,

meaning 68 degree Fahrenheit water for an hour,

experienced a 93% increase in metabolic rate,

which is remarkable given that the water wasn’t that cold,

and yet an hour is a pretty long time to be in there.

And again, it speaks to the dramatic effect

of heat transfer that water has,

which I mentioned earlier,

as opposed to being out in the air at 68 degrees,

it would certainly not cause that increase

in metabolic rate.

The group that was at 14 degrees Celsius,

meaning 57.2 degrees Fahrenheit water for an hour,

experienced a 350% increase in metabolism.

So huge increases in metabolism.

Now, the most interesting data to me,

at least in terms of mental effects

of deliberate cold exposure,

were that the plasma or serum levels

of norepinephrine in the blood increased 530%.

These are huge increases in norepinephrine.

So it suggests that this is a stressful stimulus,

at least neurochemically speaking, stressful,

despite the fact that it’s not super, super cold.

Although 57.2 degrees Fahrenheit, 14 degrees Celsius

is not a, you know, it’s not a warm environment,

but it’s not a ultra, ultra cold environment,

but an hour is a very long time to be in there.

The subjects also experienced a 250% increase

in dopamine concentrations,

which while not 530%, as it was with norepinephrine,

is still a very large increase

in baseline levels of dopamine.

And what was interesting is that those increases

in dopamine persisted for a very long period

of time afterwards, even out to two hours, okay?

And they did, they stopped the study after 120 minutes

of getting out of the cold.

But nonetheless, these increases in norepinephrine

are huge and long lasting.

And these increases in dopamine

are very large and long lasting.

And I do believe that these documented effects

in humans explain much of the enhancement of attention

and of feelings of wellbeing and mood

that people typically experience

after doing deliberate cold exposure.

And the reason I say that is that if you were to go back

to the episode that I did on dopamine,

or you were to go back to the episode that I did

with Dr. Anna Lemke on addiction and dopamine,

what you would find is that increases in dopamine

of the sort evoked by deliberate cold exposure

are actually very similar to the kinds of increases

in dopamine that are elicited by things like nicotine

or from other behaviors that are known to be addictive

and bad for us because they lead to other effects

on the brain and body that we simply don’t want.

And yet deliberate cold exposure provided it’s done safely

can create similar, if not greater increases in dopamine

that are not just fleeting,

that don’t just occur during say the consumption

of some deleterious drug or activity,

but that are very long lasting and that can be leveraged

toward activities other than deliberate cold exposure.

So I want to emphasize this.

I’m not suggesting that people do deliberate cold exposure

for an hour a day.

And unfortunately there are not many studies

yet exploring how shorter,

colder temperature environment exposure,

say one minute or three minutes or six minutes

at 55 degrees or at 50 degrees,

whether or not that leads to similar, greater

or reduced levels of dopamine in the brain and body.

And yet almost everybody who does deliberate cold exposure

will say, yeah, it was stressful.

I didn’t enjoy it, or I eventually grew to like it,

but that I always feel better afterwards.

And then that feeling lasts a very long period of time.

And I think it’s almost certain that those experiences

that people report relate to these increases in dopamine

and in concert with the increases in norepinephrine

also explain the other effect that’s commonly reported,

which is an enhancement in mental acuity

and the ability to focus.

Now here we can extrapolate to the study that I discussed

at the early part of the episode where I was talking

about the use of short 15 minute exercise,

kind of moderate intensity exercise,

and how that was shown to increase levels of energy

and mental acuity in these working memory

visual attention tasks.

And there again, we have to assume somewhat

because they weren’t doing neurochemical measurements,

but we can reasonably assume that those improvements

in cognitive performance were due at least in part

to the increase in catecholamines known to accompany

moderate intensity zone to cardio.

So what you’re starting to see here is a theme.

The theme is that virtually any stimulus

that delivers more norepinephrine, epinephrine,

and dopamine to our system will sharpen our mental acuity

and elevate our mood and will do so for some period of time.

Deliberate cold exposure, it turns out,

is a very potent way to increase these catecholamines,

this category of chemicals, and thereby to improve mood,

mental acuity, and levels of alertness.

And as we’ll next see, it not only has that effect,

which can be very beneficial for many people

in a bunch of different circumstances,

but it also has the positive effects

that many people seek in terms of metabolism,

in lowering inflammation in the body,

and other physiological effects as well.

And forgive me, I was almost ready to move on

to effects of deliberate cold exposure

on metabolism and inflammation and so forth,

but I neglected to point out

one of the other very interesting aspects

of the study showing deliberate cold exposure

can increase norepinephrine and dopamine,

which is that they observed no significant increases

in the stress hormone cortisol.

And that is both surprising, interesting, and important,

because what it means is that the quality of stress

that deliberate cold exposure is creating in the body

is likely to be one of what we call use stress.

Hans Selye, the great physiologist,

won a Nobel prize for distinguishing between distress,

which is stress in the brain and body

that causes the release of things like cortisol

along with the other catecholamines

and that we experience as negative happening to us

and can lead to negative health outcomes.

And he distinguished that from use stress,

which was stress that we now understand

is associated with increases

in things like norepinephrine and dopamine,

but no increases or minimal increases in cortisol,

and that can lead to positive health outcomes.

So it appears that deliberate cold exposure

can create what we call or what Hans Selye called use stress.

In other words, it can create a condition

in the brain and body in which we are stressing ourselves,

we are training up resilience,

and yet we are creating a neurochemical milieu

that actually has many health benefits.

Now I’d like to shift our attention

to the effects of deliberate cold exposure on metabolism.

And I’d like to start by detailing a study

that was performed on humans

and published just at the end of last year.

The title of the study

is Altered Brown Fat Thermoregulation

and Enhanced Cold Induced Thermogenesis

in Young Healthy Winter Swimming Men.

And I should point out

that while the study was only performed on male subjects,

there’s no reason to think that the effects

that they discovered would only pertain to men.

I would hope that they would also do a study on women

at some point in the future,

but the effects that they describe

are very basic core physiological processes.

What they did is they looked at deliberate cold exposure

in this group of young men,

and they used that 11 minute threshold per week.

So in other words, they had them get into cold water

for approximately 11 minutes per week.

And again, that’s 11 minutes total per week.

They divided that into two sessions,

although in speaking with the first author of the study,

Dr. Susanna Soberg,

I learned that it probably is not important

that it be two sessions,

it could be three or even four sessions,

as long as it reaches that 11 minute threshold.

What they discovered was that

by going into these cold environments,

in this case, cold water immersion up to the neck

for 11 minutes total per week,

that these men experienced increases

in so-called brown fat thermogenesis,

I’ll talk more about what that is in a moment,

and increases in core body temperature

that translate to increases in core body metabolism.

Now, the overall increases in core body metabolism

that they experienced were not extremely large.

They were statistically significant,

but they weren’t extremely large.

However, the changes in brown fat stores

are perhaps what’s most interesting about this study.

And I’ll tell you why.

The metabolic increases of deliberate cold exposure

are both acute, meaning happening in the short term,

when you get into the cold and immediately after,

one does experience an increase in core metabolism.

You burn some calories, in other words.

And while those might not be very significant increases,

or I should say they can be statistically significant,

but they are not enormously large numbers

of calories burned,

the longer lasting effects of deliberate cold exposure

on metabolism seem to take place by changes that occur

in the types of fat that we store in our body,

and the way that that fat impacts our metabolism

at other times throughout the 24-hour cycle.

This actually has a somewhat anecdotal basis,

in particular in Scandinavia.

I don’t speak Swedish, nor I speak Danish,

nor do I speak Norwegian, but I do have Danish relatives,

and they were able to help me decipher

a common Swedish saying,

which essentially translates to the fact that

in preparation for the summer, they say,

one should expose themselves to warm environments

so that one is comfortable

in warm environments in the summer.

That’s one half of this traditional Swedish

and also Danish saying.

The other half of this traditional Danish-Swedish saying

is that in preparation for winter,

in order to not feel too cold in cold environments,

one should prepare for those in the fall

by not wearing a jacket

and exposing oneself to cold environments.

Now, of course, this is just anecdotal cultural lore,

but it actually has a physiological basis,

which is by exposing oneself to cold environments

on a repeated basis in anticipation of exposure

to more extreme cold environments,

one can feel more comfortable

in those extreme cold environments.

And that’s exactly what they observed

in this study by Soberg et al.

The men felt more comfortable in extreme cold

if they had trained through deliberate cold exposure,

which might not seem surprising at all,

but based on what we talked about earlier,

whereby deliberate cold exposure evokes this discomfort

and this experience of norepinephrine release,

at least in the short term,

then you would say, well,

shouldn’t that deliberate cold exposure

also make them feel uncomfortable,

like they really want to get out?

Well, that is true at the beginning

of a deliberate cold exposure protocol,

meaning in the first week or in the second week

or the third week.

But what one finds and what you will find

if you do deliberate cold exposure consistently

is that you will then become more comfortable

at cold temperatures

away from the deliberate cold exposure.

So whereas you might have previously been the person

who was always cold in the room with air conditioning

or always seeking a sweater, always wanting to bundle up,

you will be more comfortable in those cold environments.

And the reason for that is well substantiated

from this study and from animal studies,

whereby deliberate cold exposure

converts one particular kind of fat cell,

the white fat cell,

which is a very low metabolic output cell.

It’s basically a storage site for energy in the body,

fat cells, to a different type of fat cell,

which is the beige fat cell,

called beige because it’s actually beige

or slightly brown under the microscope,

or even to brown fat cells,

which are very dark under the microscope

and dark because they contain mitochondria

and are very metabolically and thermogenically active.

In other words, white fat doesn’t burn many calories.

It’s basically a storage site.

It’s a bank account for energy.

It’s filled with lipids and those lipids can be used

if the body needs energy.

And if it goes into a caloric deficit,

beige fat and brown fat acts as sort of a furnace

or the sort of fat that you would find in a candle,

a fuel that can increase core body temperature.

So beige fat and brown fat is very good

at raising our metabolism and helps burn white fat.

Now, of course it does that only in the context

of a caloric deficit,

but it can actually help create that caloric deficit.

Having more beige fat and brown fat

can increase your overall core metabolism.

In other words, the number of calories

that you burn per day,

and therefore the number of calories that you need

to either maintain or to lose weight.

The simple translation of this is that getting

into cold water for a total of 11 minutes, perhaps more,

but at least 11 minutes per week,

divided into two or four sessions,

can increase your core metabolism in part

by increasing your beige and brown fat stores.

And we know how that works, at least in animal models.

And there’s now reason to suspect

that the exact same mechanisms are occurring in humans.

The primary way in which deliberate cold exposure

converts white fat cells

into these more metabolically thermogenically active

metabolism increasing beige and brown fat cells

is because norepinephrine released

when we get into the cold,

binds to receptors on the surface of white fat cells

and activates downstream pathways such as UCP1.

So this is an uncoupling protein one

that acts on the mitochondrial metabolism of cells

and increases the mitochondrial output of those cells

and the mitochondrial density of those cells.

In other words, it takes a cell

that has a kind of a weak engine

or no engine for generating energy.

Although every cell has some mitochondria,

it takes cells that have very few mitochondria

and increases the engine size.

It kind of stokes the furnace of those particular cells

and actually can change gene expression in those cells.

So that’s what’s really interesting.

Deliberate cold exposure causes increases in norepinephrine

which bind to receptors on the surfaces of white fat cells,

which triggers the release of things like UCP1.

It also causes the release of things like PPAR gamma

and cofactor PGC1.

I’m going to refer you to a review

if you want to learn more about these.

For those of you that don’t want to learn more,

all you need to know is that the downstream of all that

are increases in mitochondria and metabolism

and actual genetic changes in the white fat cells

that convert them into beige and brown fat cells.

This is especially important for adults

because babies and young children

actually don’t have the ability to shiver

or they have a less robust capacity to shiver.

Very small babies really can’t shiver.

So they have a lot of brown fat in order to keep them warm.

Young children eventually develop the ability to shiver

and maintain these brown fat stores

mainly around the clavicles, the heart, the upper spine,

and in the upper back.

And it’s no coincidence that kids can often run around

with a minimal of clothing and be comfortable

in environments that adults would be cold in.

As life goes on, we tend to lose beige and brown fat,

but this mechanism that I’m referring to

points to the plasticity of white fat,

meaning the ability for white fat

to actually convert its identity

into this metabolically thermogenically enhancing form

of beige and brown fat.

So deliberate cold exposure is a terrific way

to increase your core metabolism.

And oftentimes critics will say,

well, the increase in metabolism isn’t that significant.

Although I do want to point out again,

the 93% and 350% increases in metabolism

from that previous study.

But critics then will say,

well, that doesn’t really translate to that big

of a caloric burn during the deliberate cold exposure.

But to that, you should say, ah,

but that’s only limiting your optics

to just a portion of the effects

of deliberate cold exposure

because deliberate cold exposure can also convert white fat

to beige fat and brown fat

and lead to these more lasting increases in metabolism.

So for any of you interested in increasing your metabolism

and or being comfortable in cold environments

and or being comfortable in terms of being able

to combat stress mentally,

deliberate cold exposure I do believe is a powerful tool.

And there is simply no reason why you couldn’t

and shouldn’t use the same protocols

that I described earlier for building resilience

to increase metabolism.

Provided you’re hitting that 11 minute per week threshold,

you ought to be stimulating both mechanisms,

increases in resilience and increases in core metabolism.

As I mentioned earlier,

most of the detailed studies on the conversion

of white fat to beige fat and brown fat

through the use of cold have been done in animal models,

but the human data are starting to emerge.

And if you’d like to do the deep dive into these mechanisms,

things like UCP-1, PPAR-gamma, et cetera,

there’s a beautiful review that was published recently

in the journal Cell,

which is one of the three apex journals,

Nature Science Cell.

And the title of that paper is

Adipose Tissue Plasticity in Health and Disease.

I love this review.

It has beautiful diagrams detailing all of the pathways

from cold to norepinephrine through UCP-1,

downstream of things like cyclic AMP.

If none of those names mean anything to you,

don’t worry about it.

You certainly don’t need to know these mechanisms

to benefit from deliberate cold exposure protocols.

If those names do mean something to you,

or you’re interested in exploring the downstream effects

of deliberate cold exposure,

and something else that’s really nice

that’s covered in this paper

is how deliberate cold exposure interacts

with fasted states and fed states.

I think you’ll also find this review very interesting.

I don’t want to go too deeply into fasted states

and fed states right now.

Suffice to say that when we are fasted,

meaning when we haven’t eaten for some period of time,

our baseline levels of norepinephrine and epinephrine

are already elevated.

And so cold exposure at those times

ought to have an even greater effect

on metabolism and resilience and so on.

So for you fasters or your intermittent fasters out there,

if you really want to get fancy,

you can do your deliberate cold exposure

when you are fasted.

I certainly wouldn’t recommend doing it

with a very full stomach in any case.

And as I mentioned before on this podcast,

intermittent fasting is but one way,

and certainly there are other ways

to limit total caloric intake

for sake of maintaining or losing weight,

if that’s your goal.

I know many people are using and benefit

from intermittent fasting, however,

and so it certainly can be combined

with deliberate cold exposures

in order to get even greater increases

in norepinephrine and epinephrine.

So for those of you that are primarily interested

in using deliberate cold exposure

to increase dopamine levels in your brain and body,

you can also do a combined protocol

whereby you ingest caffeine 60 to 120 minutes

before the deliberate cold exposure.

This is based on a study that I’ve talked about before

entitled Caffeine Increases Striatal Dopamine

D2, D3 Receptor Availability in the Human Brain.

And as the title suggests, this study was done on humans

looking at the density and or efficacy

of these dopamine receptors

in an area of the brain called the striatum,

which is involved in planning and action

and also suppressing planning and action.

It’s involved very closely

with whether or not we can engage in behavior

and withhold behavior,

the so-called go and no-go pathways in the brain.

Dopamine plays a critical role in that

and many other things as well as you now know.

So why would you want to ingest caffeine 60 to 120 minutes

before deliberate cold exposure?

Well, as I talked about earlier,

dopamine can increase quite substantially

in response to deliberate cold exposure,

but dopamine on its own doesn’t do anything.

It has to bind to receptors.

And this paper shows quite definitively

that ingesting caffeine, in this case,

it was 300 milligram dose of caffeine,

which is about the dose of caffeine

in two or three cups of coffee.

It depends on the strength of the coffee, of course,

but it’s not an outrageous amount of caffeine.

That increases the density

and or efficacy of these receptors,

which would allow that dopamine to have its greatest effect.

And for those of you that want to get really, really fancy,

I suppose you could do this fasted.

So you get the further increase in norepinephrine,

then you get the dopamine increase from the cold exposure,

the binding of the dopamine.

Although I do want to point out that at some point

you start layering together enough protocols

that you would be spending your entire day

trying to get this dopamine pulse.

And I would hope that you would have other activities

that you would engage in.

But if you’re getting up in the morning

and you’re fasted because you haven’t eaten all night

and you have a cup of coffee,

and then 60 minutes later you take your cold shower

or two hours later you do your cold immersion

or your cold shower,

you would be layering together these different mechanisms

of dopamine receptors, epinephrine, and so forth

in a way that at least to me doesn’t seem incompatible

with having some other life,

like going to school and having relationships, et cetera.

And this increase in dopamine,

particularly in the striatum is not a trivial one.

I do want to point out as the authors do

that preclinical studies have shown

that increases in striatal dopamine

induced by things like modafinil,

which is used to treat ADHD and treat narcolepsy

is necessary for their wake promoting actions.

What this really says is that

just having elevated levels of dopamine from a drug

or from an ice bath or what have you

is not sufficient to get the effects of dopamine.

You really need the receptors to be available

and you need those receptors to be available

in the appropriate density

and you need those receptors to be available

in the appropriate density in the striatum in particular.

So I think there are a number of reasons why

if it’s compatible with the other aspects of your health,

because of course always you have to consider this

on a background of cardiovascular health

and blood pressure, et cetera,

that ingesting a cup or two of coffee

an hour before your ice bath, maybe fasted as well,

could be quite beneficial for increasing dopamine

over quite extended periods of time.

A couple of key points that you’ll want to pay attention to

in thinking about deliberate cold exposure and metabolism.

In the Soberg study, they also explored the use of sauna

and how to use sauna, meaning deliberate heat

in conjunction with cold.

We are going to do an entire episode

about the use of heat for health and performance.

So that is not the focus now.

However, it does raise an important point

that we do need to address at this moment,

which is if you are using sauna

or if you are taking warm showers,

or if you’re simply using deliberate cold exposure

of any kind, should you get into the heat afterward

or before or not at all?

And this is where we can point

to the so-called Soberg principle.

At least I call it the Soberg principle.

The Soberg principle named after first author

of this study I referred to earlier, Dr. Susanna Soberg.

In science, it is appropriate to take a key piece of data

and call it a principle.

If in fact it translates to something larger,

which I believe it does.

It is generally not appropriate for people

to name a principle after themselves,

although there are a few scientists that have done that.

So I have named it the Soberg principle,

but I did that to give it appropriate credit

to Dr. Susanna Soberg, who discovered that

and pointed out quite appropriately

that to achieve the greatest increases in metabolism

through deliberate cold exposure,

you want to force yourself to reheat on your own

after the deliberate cold exposure.

Meaning you wouldn’t want to go from the cold shower

to a hot shower or from the cold shower to a sauna.

Rather, if you were going to start with a hot shower

or you’re going to start with a sauna,

that you would end with the cold

and then you would reheat naturally.

Now, I personally take a cold shower.

I do a few times a week or do cold immersion.

And because I’m not specifically focused

on increasing metabolism, although I probably should be,

that’s not what I’m using it for now.

I will take a hot shower afterwards.

And in doing so, I’m short-circuiting

some of the further metabolic increases

that I would achieve were I to just end with the cold.

So the Soberg principle is,

if you want to increase your metabolism, end with cold.

And we can take this a step further

and say that if you want to use deliberate cold exposure

to increase metabolism, that you should make sure

that you get to the point where you shiver.

And the reason for this is that there are a series

of studies, but in particular, one study published

in the journal Nature, excellent journal in the year 2018,

showing that deliberate cold exposure

that evokes shivering from the muscles

causes the release of a molecule called succinate

from the muscles.

And that succinate plays a key role

in activating brown fat thermogenesis,

which you now have heard about and understand

as critical to the increases in metabolism

caused by deliberate cold exposure.

So what this means is if you want to increase

your metabolism, end on cold, that’s the Soberg principle.

And as best you can, try and get to the point

where you are shivering,

either when you are in the cold exposure

or immediately afterwards.

Now, one efficient way to do this is to, for instance,

you could get into the cold shower for a minute

or two minutes or three minutes, uncomfortably cold,

but safe to stay in.

Remember, that’s our general rule of thumb.

Then turn off the water and stand there.

Make sure that you’re not holding yourself

close to your body.

You’re not hugging yourself to try and keep yourself warm,

but rather your limbs are extended at your sides.

And then if that fails to induce shiver,

then to turn on the cold water again

and then turn it off again.

So alternating perhaps a minute to three minutes

of cold exposure followed by a minute to three minutes

of drying out in air and going back

into the cold exposure, et cetera.

I can tell you this from experience.

This is a pretty brutal protocol.

If you have never tried getting into an ice bath

or cold water immersion or cold shower for one minute

and then getting out and trying to stand there

with your arms extended in cool or cold air

for one minute and then getting back into the cold shower

or water immersion, you are in for an experience

because even for those of you

that are pretty shiver resistant,

you will find that it is much, much harder

to get out of that cold water and stand there,

arms extended and drying off by evaporation,

which further draws heat from the body

than it is to wrap yourself in a towel,

get in a warm shower or a sauna.

So there’s certainly no requirement to end on cold.

There’s certainly no requirement to induce shiver,

but if your primary goal is to induce increases

in metabolism, both in the short-term and in the long-term

following the cold exposure,

well, then you’ll want to end on cold

and you’ll want to find a way to shiver

provided that the level of cold

that you’re exposing yourself to

is still safe for you overall.

So up until now, I’ve been talking

about deliberate cold exposure as a potent stimulus

for the release of norepinephrine in the brain and body.

And indeed it is, but the way I’ve been describing it

has been in the context of circulating plasma levels

of norepinephrine, meaning circulating within the blood.

What I haven’t mentioned, but is absolutely true,

is that the fat cells themselves

actually receive input from neurons.

So there are neurons that release norepinephrine

in response to cold directly into the fat.

So I want to give you this picture

of how the architecture of all this works

because I think it can help you navigate

and indeed build better deliberate cold exposure protocols.

Your adrenal glands release norepinephrine and epinephrine.

Your brain has sites within it like the locus coeruleus

that release norepinephrine and epinephrine.

But there are also neurons within your skin that sense cold

and other neurons that can directly release norepinephrine

into the fat stores and cause those white fat cells

to convert to beige and brown fat.

And I think this particular aspect of our physiology

is often overlooked in studies.

And when people say,

well, the increases in metabolism aren’t that great,

the circulating levels of norepinephrine,

those are very large, but they’re very transient and so on,

that fails to understand that neurons

that actually sense cold are in a position

to communicate via other neurons

directly to the fat cells

and release norepinephrine into those fat cells,

which as I pointed out earlier,

set off a huge set of immediate and long-term cascades

of even gene expression changes.

So the picture that I’d like you to have in your mind

is that when you get into the cold,

yes, of course, you experience that as a experience of,

I don’t want to do this, I’m going to overcome this,

I’m going to climb over these mental walls

that represent adrenaline release in my brain and body,

but also that your fat cells are receiving signals,

norepinephrine signals that are changing those fat cells

in the way that they metabolize energy.

Now I’d like to shift our attention

to the use of deliberate cold exposure

for sake of physical performance.

And there are a lot of opinions out there

about the use of deliberate cold,

whether or not it should be done, for instance,

before or after exercise,

whether or not if done immediately after strength training

or hypertrophy training,

meaning training designed to grow muscles

or make them stronger,

whether or not it can inhibit that process

and so on and so forth.

I think today in looking over the literature

and trying to bring forward the simplest

and most straightforward

and yet scientifically grounded protocols,

we can set up some general guidelines

that will allow most if not all of you

to still extract the benefits of deliberate cold exposure

on physical performance

without getting too neurotic about the exact timing.

But for sake of discussion

and because it’s a prominent theme

in many online communities,

let’s just start with the big one out there,

meaning the question of whether or not doing an ice bath

or doing deliberate cold exposure

or taking a cold shower

after strength slash hypertrophy training,

meaning training designed to increase strength

or, and, or I should say the size of muscles

will somehow short circuit or diminish that process,

whether or not it will reduce

or eliminate those strength gains and hypertrophy gains.

And the short answer that I was able to arrive at

on the basis of a review article

that I’ll talk about in a moment

and some other studies as well

is that if your main goal is hypertrophy and strength,

it is probably best to avoid cold water immersion

and ice bath immersion

in the four hours immediately following that strength

and or hypertrophy training.

Again, if your main goal is to achieve hypertrophy

or strength or some combination of those,

probably best to avoid cold water immersion up to the neck

or ice bath immersion up to the neck

immediately after strength and hypertrophy training

and extending out to about four hours after that training.

If you’re really neurotic about this,

then perhaps you’d want to move the cold water exposure

to a different day entirely,

but it all depends on how neurotically attached you are

to getting every last bit of strength and hypertrophy.

And if that’s your goal, terrific.

Well, then probably moving the cold exposure

four hours or more away from that training

is going to be necessary for you.

Now you’ll notice I did not talk about cold showers.

And the reason I did not talk about cold showers

is that there simply are not very many studies

of deliberate cold exposure through cold showers

for the reasons I talked about

at the beginning of the episode.

It’s hard for me to imagine that taking a brief cold shower

after a strength or hypertrophy training session

would completely reverse or short circuit

the effects of that strength and hypertrophy training.

But again, if you’re neurotically attached

to getting every last bit of strength and hypertrophy

out of your training sessions,

then by all means err on the side of caution

and wait four hours or more to do your cold shower

just as you would wait four hours or more

to do your cold water immersion.

Now there are nice data pointing to the fact

that doing cold water immersion after a hard run,

so endurance training or even sprint and interval training,

or after a weight workout where your main focus

is on performance of those movements,

or after a skill training workout

where your main focus on performance of those movements,

that there’s no reason to think

that that cold water immersion or ice bath or cold shower

would inhibit the progress or the stimulus

that would lead to progress

that occurred during that training session.

In other words, I don’t see any reason

based on the literature

to avoid deliberate cold exposure immediately after training

again, unless your goal is hypertrophy and strength.

And in fact, there’s a very nice review

that was recently published on deliberate cold exposure

and how it can impact physical performance,

whether or not it’s done before or after

different types of training and so forth.

The paper is entitled,

Impact of Cold Water Immersion

Compared with Passive Recovery

Following a Single Bout of Strenuous Exercise

on Athletic Performance in Physically Active Participants,

a Systematic Review with Meta-Analysis and Meta-Regression.

So this is a meta-analysis of 52 studies

that looked at a tremendous number of variables

and contexts as you would expect

in a meta-analysis of 52 studies.

I’m going to read you the conclusions of the study

and I will provide a link.

We certainly don’t have the time

to go through all the details of the study.

I will highlight a few specific outcomes

that I found particularly interesting,

but here I am paraphrasing their conclusions

that cold water immersion,

I want to emphasize immersion, not cold showers,

but cold water immersion,

they say was an effective recovery tool

after high intensity exercise.

They observed positive outcomes,

meaning improvements in certain variables

for muscular power, muscular soreness,

meaning reduced muscular soreness,

increased muscular power,

perceived recovery after 24 hours of exercise.

However, there were certain forms of exercise

that were not benefited by cold water immersion,

such as eccentric exercise,

exercise focusing only on the lowering component

or the so-called eccentric component

of resistance exercise.

They saw some very interesting dose response relationships

for things like endurance training,

meaning the longer the cold exposure,

post-endurance training,

the more improvement in endurance performance,

reductions in circulating creatine kinases

and things that relate to muscle damage

under certain conditions.

Some point in the future, by the way,

we’ll do an entire episode

on creatine and creatine kinases,

which are important not just for muscular function,

but also for brain function.

But the basic takeaway was that cold water immersion

performed after high-intensity exercise

was beneficial from a number of different standpoints

and indicated that shorter duration cold exposure

and lower temperatures can improve the efficacy

of cold water exposure

if used after high-intensity exercise, okay?

There I’m directly pulling from their conclusions.

So what this says is that it’s not just those

longer duration, 30, 45 minute, and 60 minute protocols

of cold water immersion that we discussed earlier,

but also shorter duration, one minute, three minute,

five minute exposures to lower temperatures,

temperatures that would make you psychologically

want to get out as soon as you possibly can,

but again, that you can safely stay in,

done after training really have been shown

to improve outcomes in terms of reducing soreness

and improving training efficacy,

meaning your ability to get back into training more quickly

and thereby deliver more training stimuli to a given muscle

or in your endurance training protocol.

Translate to English what this means

is that taking a cold shower or getting into an ice bath

or some other form of cold water immersion

within the immediate minutes

or even the immediate hours following your training

has been shown to be beneficial.

I’m sure a number of you have questions, for instance,

how long should you be in that cold exposure?

Is it the same as the 11 minute threshold described earlier?

To be honest with you,

there are not enough studies to really point

to the critical threshold for eliminating

or reducing delayed onset muscle soreness

or for getting maximal results

from power and endurance training,

but this study does make a couple of key points

and here I will just paraphrase.

For instance, that cold water immersion

is more likely to positively influence

muscular power performance,

to reduce muscle soreness,

to reduce serum creatine kinase

and to improve perceived recovery

after high intensity exercise

as compared with passive recovery.

This can be translated to cold water exposure

after training is beneficial

and probably better than passive recovery

from a number of standpoints.

In addition, they say that dose response relationships,

meaning the amount and the degree of cold

that people were exposed to

and how often they did that

in particular in lower temperature cold immersion.

So these would be the sorts of cold immersion protocols

that are one minute or two minutes,

three minutes, maybe five minutes,

but that one couldn’t stay in there longer

because it feels stressful and one wants to get out,

may be more effective after high intensity exercise

for removal of serum creatine kinase

as well that these shorter duration

cold water immersion approaches

may be more effective

after high intensity endurance performance as well.

So all of this can be translated to say

that unless your main goal is hypertrophy and strength,

that cold exposure, ideally cold immersion

in cold water or ice bath,

but if you don’t have access to that,

then cold showers is likely going to be beneficial

if done immediately after

or in the minutes or hours after your training,

especially high intensity training.

One particularly nice thing about this meta-analysis

is that it included some studies

that involve the use of cooling packs.

So again, vests that can hold essentially ice packs

and indeed even cryotherapy chambers and so on.

There’s a nice table in the study.

If you want to get really detailed

and go and look specifically at those studies,

I invite you to do that.

We’ll put a link to this study

in the caption for this episode.

But all in all, what this study shows

is that deliberate cold exposure

can be very useful for recovery,

likely through reductions in inflammation

in muscle and connective tissue.

And while this study did not look specifically

at the mechanisms of reduced inflammation

caused by deliberate cold exposure,

those mechanisms are somewhat known.

There are a number of studies that have pointed to the fact

that deliberate cold and cold generally

can reduce inflammatory cytokines,

such as IL-6, interleukin-6.

It can increase anti-inflammatory cytokines,

such as interleukin-10 and so on.

Without getting into all those details,

I think it’s sufficient to say that

if you are somebody who experiences

a lot of delayed onset muscle soreness,

taking a cold shower after your training

or getting into a cold immersion after your training,

even if it’s a few hours later, ought to help.

And if you are doing particularly intense training,

then you probably want to ratchet up

the number of cold exposure sessions that you’re doing,

even if those have to be done

on separate days from your training,

because a lot of the inflammatory effects of training,

endurance and strength training,

are actually occurring some hours

away from the training stimulus.

So it’s not just that inflammation

goes up radically during training, which it often can,

but that it can occur even in the days

and even weeks afterwards, depending on how intense

and how long duration that training is.

So deliberate cold exposure is very powerful

as an anti-inflammatory tool.

Now, I’d like to emphasize the topic that we touched on

at the beginning of the episode,

which are those glabrous skin surfaces,

the hands, the upper face, and the bottoms of the feet,

through which heat is especially good at leaving the body.

And another way of putting that is that one can cool

the body much more efficiently

through the glabrous skin surfaces.

Now, if you want to understand all of the science

behind this and all of the various applications,

I invite you to please listen to the episode

that I did with Dr. Craig Heller,

again, in the biology department at Stanford.

For sake of this episode, I’m just going to detail

a couple of findings from his laboratory.

The first one dealing with exercise-induced hyperthermia,

because I think this is very interesting

and it can even save lives

if you understand the way this works.

There’s a particular paper that focuses on this,

and we will put a link to this as well.

The title of this paper is

Novel Application of Chemical Cold Packs

for Treatment of Exercise-Induced Hyperthermia,

a Randomized Control Trial.

This is a pretty brutal study,

brutal for the subjects, that is.

What this study involved was having subjects

walk on a treadmill at a pretty significant incline,

anywhere from nine to 17%,

wearing a substantial amount of clothing

that was not well-ventilated,

and the room was kept to 40 degrees Celsius,

which is 104 degrees Fahrenheit.

This is definitely not something to do at home.

This study was designed to induce hyperthermia,

which, as I mentioned earlier, can be quite dangerous.

And they compared two types of cooling.

In the first form of cooling

that they call traditional cooling,

they had ice packs on their neck,

in their armpits, and in their groin.

And in the other group,

there was the so-called glabrous skin cooling.

So the palms, the soles of the feet,

which were actually,

so they were cooling inside the boots or inside of gloves,

and on the upper portion of the face.

And the basic takeaway of the study

is that by cooling the glabrous skin,

the subjects were able to sustain this walking

on these inclined treadmills for much longer

than were the people who received traditional cooling.

And also the return to baseline temperature

was much faster in the glabrous skin cooling group.

So how this translates to the real world

is that if ever you are hyperthermic

or someone else is hyperthermic,

one way to cool them down quickly

is to cool these palmar glabrous,

soles of the feet glabrous,

and upper portion of the face glabrous portions of the body

using cool rags, using ice packs,

or using any number of different

cold objects or temperatures.

One key thing, if you’re going to use glabrous skin cooling,

is that whatever you use to cool those surfaces

cannot be so cold that it causes vasoconstriction.

Because as I mentioned earlier,

the arteriovenous asthmoses,

these portals of arteries directly to veins

that exist only in these glabrous skin surfaces,

the way that they’re able to cool the body

and essentially pass cool into the body,

although that’s not really what they’re doing,

they’re actually extracting heat from the body,

to be technical, they’re extracting heat from the body,

the only way they can do that

is if those veins don’t collapse,

and veins will collapse if they are made very, very cold.

So if you want to use glabrous skin cooling

to offset hyperthermia,

or for the other forms of performance,

which we will talk about in a moment,

you need to use a cool object or surface

that is not so cold that it causes vasoconstriction.

And this can be a little bit tough to dial in,

meaning it can be tough to identify such an object.

And for that reason, Dr. Heller and some of his colleagues

have developed a commercial product called the CoolMitt,

you can actually go to their website, coolmitt.com,

I don’t have any financial or other relationship to them.

I know they’ve been developing this technology

for some period of time,

it involves a glove that you put your hand into,

it circulates water of a given temperature,

and it does so at a temperature

that is sure to not cause vasoconstriction of the palm.

And you may be asking,

how can you just put your hand into one glove

and have this work?

Well, that’s how powerful these glabrous skin surfaces are.

Even just by cooling one palm,

the core body temperature drops radically.

Now, that’s their commercial technology.

I know that some people out there

have started to experiment with a home version of this,

which would be taking a package, for instance,

of frozen blueberries or some other cold drink

or cold metal object and actually bringing it into the gym

or out on a run.

There are even people who are now developing

cooled bicycle handles for long rides.

This might seem a little kooky or crazy to you,

but as you’ll soon hear in the study I’m about to describe,

the increases in endurance

and in the volume of strength training

that people can conduct

if they appropriately cool their body

through these glabrous skin portals

is actually quite significant.

So again, as it relates to hyperthermia,

if someone is overheating,

by all means, try and get them out of that heat,

get them to stop exercising.

You can die from hyperthermia.

Try and cool the bottoms of the feet,

the palms of their hands,

and the upper portion of their face.

That does not mean that it would be a bad idea

to put cold water on the top of their head.

That probably would also help, and perhaps on their neck.

What is probably not going to be a good idea

is to do the more standard thing

of draping someone in cold towels

on the surface of their body,

because as I mentioned at the beginning of the episode,

that thermostat in the hypothalamus,

the medial preoptic area,

will typically react to that

by increasing core body temperature further.

The effects of glabrous skin cooling

on physical performance are truly remarkable

provided the glabrous skin cooling is done correctly.

And I want to point out

that the main degree of effect is on volume

or the ability to do more work.

And I want to point this out

because I think that many people,

certainly in the exercise science community,

but even in the general public,

when they hear about some of these effects

that are measured in the laboratory,

they sort of look at those effects a bit askance,

and they think, well, that’s not possible, right?

Effects, for instance, that have been documented

showing doubling or tripling of the number of dips

that one can do in a relatively short amount of time,

or doubling of the number of pull-ups one can do,

or 14% increases in strength,

or even comparable degrees in increase

in weight training output

to people who are on performance-enhancing drugs,

et cetera, et cetera.

Part of the confusion is that

the effects of proper palmer cooling,

because it almost always is done by palmer cooling

and less often in these experiments

by cooling of the bottoms of the feet

and the upper portion of the face,

but those effects tend to be

the ability to do more work over time.

And just to illustrate some of the major effects

that the Heller lab has seen,

and that are documented in this manuscript

that I’ll share with you in a moment,

the typical protocol is to have people come in

and do some endurance training,

so running on a treadmill,

and to have a condition where

one group is actually doing palmer cooling

while they are on a bike or on a treadmill,

and inevitably the outcome is that they can do more work.

They can pedal further at a given speed,

or they can run longer at a given speed

than people who are not doing palmer cooling,

or who are receiving cooling

by way of cold compress to the back of the neck

or ice pack to the armpits, et cetera.

So the effects of palmer cooling

are very clear and very robust.

And in the context of endurance exercise,

almost always allow people to do more work,

to go longer with less perceived effort

and to quit later, so to speak.

In terms of strength training,

they’ve looked at the capacity to perform sets of dips.

So one of the more famous examples of this

that Dr. Heller shares in the episode that we did earlier,

and that you can find at hubermanlab.com,

involves someone coming in and doing sets of dips,

maybe 40 dips,

this person actually could do 40 dips on their first set,

then resting for a period of two to three minutes,

and then doing 35,

and then resting for a period of two or three minutes,

and then doing progressively fewer and fewer and fewer

to the point where over a period of time,

they add up the total number of dips that they can do,

and then they have them come back

after a period of recovery.

So not immediately after, but take a couple of days,

come back and do effectively the same protocol,

but during their rest periods,

they’re doing two minutes of palmer cooling,

which essentially allows heat to move out of the body,

lowering core body temperature, in other words.

And what they find is that they see enormous increases

in the total number of dips that people can do,

but that doesn’t mean that the person goes

from being able to do 40 dips

to being able to do 50 dips or 60 dips on that first set.

What it means is that they are able to do 40

on the first set, then 40 on the second,

then 38 on the third, and so on and so forth,

so that the total duration of the workout is extended,

and yet they’re doing much more work,

even though it takes more time.

So that’s an important point,

and I think a point that perhaps wasn’t as clear

or as clearly made by me in the previous episodes

that discussed this topic.

For those of you that are interested

in exploring palmer cooling,

first of all, I recommend taking a brief glance

or even a deep dive into this study,

which is entitled Work Volume and Strength Training Responses

to Resistive Exercise Improve

with Periodic Heat Extraction from the Palm.

In this study, they describe big increases in anaerobic,

meaning strength training output,

things like improvement in dips,

improvement in bench press,

improvement in pull-ups, et cetera, in human subjects.

And it’s a really nice study

and points to some of the protocols

that you might be able to adapt in your own setup.

For instance, over six weeks of pull-up training,

palm cooling in between sets,

improved volume by 144%,

and this was in experienced subjects.

So that’s interesting,

because a lot of studies of strength training

and improvements in hypertrophy and strength

are done in inexperienced, untrained athletes,

which changes the picture somewhat

compared to experienced athletes.

They found that strength,

meaning the one repetition maximum,

increased 22% over 10 weeks in bench press training.

And they point to the particularly strong effects

of using palmer cooling when people reach plateaus

in endurance and strength training.

And there, I think it’s an important point.

I think that if you’re going to explore palmer cooling,

it’s probably not the sort of thing

that you’re going to do in every run

or in every bout of cycling

or in every strength training session,

but that it might be used to vastly increase your volume

or vastly increase your endurance in a given session

or a set of sessions in order to push through plateaus.

A particularly interesting point in light of that

is Dr. Heller has observed again and again

that palmer cooling reduces delayed onset muscle soreness

or can eliminate it entirely.

And that’s very interesting

because it also points to the fact

that reducing core body temperature

may somehow be involved in short circuiting

the normal mechanisms of delayed onset muscle soreness.

And you might say, well, how would temperature be involved

in delayed onset muscle soreness?

Well, I want to refer you back to the meta-analysis

that we talked about earlier,

where the short duration,

very cold temperature exposure after training

did indeed reduce delayed onset muscle soreness

in part through reduction, excuse me, in creatine kinase.

So it’s not inconceivable that temperature

and delayed onset muscle soreness are related.

And that raises perhaps the most important point,

which is the way that palmer cooling can improve performance

by way of reducing core body temperature is known.

And that is because when one engages in exercise

or muscular output of any kind,

strength or endurance exercise,

the range of temperatures under which a muscle can perform

is actually very narrow.

There’s an enzyme called pyruvate kinase,

which is critical to muscle contractions.

And pyruvate kinase can only function

in a very narrow range of temperatures.

If that temperature gets too hot,

meaning if the muscle heats up locally,

whether or not by running or cycling or swimming

or weightlifting, the ability for that muscle

to continue to contract is reduced

and eventually is short-circuited completely.

And I think this is a much underexplored

or at least a much under-discussed aspect

of so-called muscular failure

or the failure of one to continue to endure in running.

So for instance, when you run

as compared to a bench press or something,

you don’t stop running

because you can’t actually contract the muscles further,

but somehow signals about the heating up of muscular tissue

are conveyed to the brain.

There’s a crosstalk there.

It’s probably bi-directional and people stop.

They quit, right?

This is the quitting reflex.

In strength training,

one can no longer perform a repetition

or set of repetitions in part

because of heating up of the muscle locally.

There are other mechanisms as well, of course,

and I realized that.

But what’s very clear from the Palmer cooling work

is that by simply holding onto a cool object,

remember, not an object so cold

that it constricts the vessels of the palms

or constricts the vessels on the bottoms of the feet,

but by holding onto a relatively cool object

in one or both hands in between sets for two minutes or so,

you can very efficiently reduce your core body temperature.

And in doing so,

reduce the temperature of the muscles

that are doing the work,

increase the capacity for pyruvate kinase

to continue to allow your muscles to contract

and thereby allow you to do more volume of endurance

and strength training.

So a simple protocol that Dr. Heller passed to me

is find a relatively cool object.

So you could, for instance,

fill two bottles with cold water,

maybe put a few ice cubes in there, right?

This is not exact

because we’re not talking about

the commercial CoolMitt product here.

We’re talking about an at-home version

or use a pack of frozen blueberries or broccoli,

the sort of pack of those as what he described.

And then in between sets to put your hands,

and ideally you’d put the bottoms of your feet,

but that’s not always feasible in most gyms

where they won’t let you take off your shoes and so forth.

But to put the palms of your hands on that cool surface

for a minute or two minutes between sets

and then returning to your sets of work.

Now, if you are heating up through other mechanisms,

like you’re wearing a stocking cap

and you’re in a very warm environment,

this might not have as potent an effect

as if you were to do this cooling

in a more moderate environment,

wearing lighter clothing, et cetera.

So by all means, warm up to do your exercise,

lubricate your joints and get into a place

where you’re not going to injure yourself

doing whatever form of exercise you do.

But then if you’d like to explore palmer cooling,

I know a number of people who’ve written to me saying

they heard about palmer cooling

on the episode with Dr. Heller.

They’ve tried this and they see quite excellent results.

It does take some discipline, right?

It’s one thing to just kind of hang out in the gym

and play on your phone in between sets.

It’s another to do deliberate cooling with your palms

or the bottoms of your feet

or the upper portion of your face.

You might get some weird looks,

but of course you’ll be the one doing

some significantly more volume,

not experiencing delayed onset muscle soreness

and achieving better endurance and strength gains

were you to do this properly.

Now, as a final topic related

to the use of deliberate cold exposure

for improving health and performance,

I’d like to touch on this theme that exists online

on social media, on YouTube,

and in various fitness communities

of using deliberate cold exposure to the groin,

in particular to the testicles

in order to try and increase testosterone.

And while this might sound really kooky,

indeed, this practice exists.

Indeed, if you were to go on the Amazon,

there are actually ice pack underwear

that are being marketed for sake of increasing testosterone.

Now I am not aware of any specific well-controlled studies

that show that this indeed works.

I can imagine based on what I know

about the nervous system, testosterone and cold, et cetera,

that there are a couple of mechanisms

by which one might experience increases in testosterone

as a consequence of deliberate cold exposure.

First off, let me say,

there is no reason why you would have to

apply these ice packs in the way that I just described.

One could, of course, take a cold shower.

One could, of course, use cold immersion of various kinds,

and you’re still going to get that exposure

of the groin and the testicles to cold.

Now I should point out that people do report,

at least anecdotally, increases in testosterone

as a consequence of this practice.

And I have to imagine

that they are measuring their serum testosterone,

that they’re not just guessing

that their testosterone went up.

If you know of a study exploring this directly,

please let me know, put it in the comment section on YouTube

or even just email me.

We have a email that you can find at hubermanlab.com.

Please email me the reference.

I wasn’t able to find a reference,

but I can imagine two reasonably plausible mechanisms

by which deliberate cold exposure to the groin

and particularly the testicles would increase testosterone.

The first is somewhat direct,

which is that anytime you cool a body surface,

that if it’s cold enough,

you’re going to get vasoconstriction.

And then subsequently,

you’re going to get a rebound increase in vasodilation,

meaning you’re going to constrict the blood vessels

in that area.

And then after the cold is removed,

there’s going to be more blood flow to that area.

And of course, blood flow relates to organ health

and tissue health generally.

So perfusion of that region and the gonads, to be specific,

with additional blood,

you could imagine in some ways increasing testosterone.

That’s reasonably plausible.

The other probably more likely mechanism

relates to the dopamine increases caused by cold exposure

that we talked about earlier.

Again, anytime you have a somewhat stressful stimulus,

but in particular with cold exposure,

it seems that the catecholamines, norepinephrine,

epinephrine, and dopamine all increase.

And dopamine is known to be in the pathway

that can stimulate testosterone.

And so while there isn’t a direct relationship

between dopamine stimulating testosterone,

there is an interesting pathway

whereby dopamine increases can trigger increases

in things like luteinizing hormone,

which can trigger increases in testosterone

as well as estrogen for that matter.

So I know that there are a lot of people out there

that are interested in the use of cold exposure

for increasing testosterone.

And some of those people in communities

are indeed using cold exposure directly on the gonads,

on the testes in order to do this.

I’m not certain that that direct contact is necessary.

And in some cases it might actually be quite dangerous

or you at least should be careful

in terms of tissues there and avoiding damage.

But nonetheless, I think that a dopamine impact

on testosterone is very likely

given the 250% increases in dopamine

that have been observed with cold water immersion.

And all of that points to the fact

that cold water immersion very likely increases testosterone

but as a downstream consequence

of the cold water immersion effects on dopamine

and luteinizing hormone.

And again, there’s no reason to think

that the increases in luteinizing hormone

would also increase estrogen.

Probably not too dangerous

or levels that one would want to avoid.

But I don’t think that there’s anything

particularly specific about cold for inducing testosterone

and not other hormones.

I think it’s very likely to increases

a number of different hormones.

I do hope that there will be a systematic study on this

in the not too distant future.

I also hope to not be a subject

in the cooling of the gonads experiment.

Now I promise you the last topic was the last topic

but there’s one other really important point

that I think everyone should be aware of

if you’re going to use deliberate cold exposure.

And that brings us back to the very first thing

that we discussed today

along the lines of deliberate cold exposure

which is that your baseline temperature

is going to be lowest about two hours before you wake up.

It’s going to increase in the morning and as you wake up

and increase throughout the day and afternoon

and then start to drop in the evening

and come down at night as you head to sleep.

I also want you to remember

that if you are to cool the external portion of your body

in particular your torso,

the net effect of that

is going to be an increase in body temperature.

So for many people, not all, but for many people

if you are going to do deliberate cold exposure

you are going to increase your core body temperature.

And that makes sense if you think about

how deliberate cold exposure can increase metabolism

by increasing thermogenesis.

What that all means is that

if you are doing your deliberate cold exposure

early in the day,

you are going to get yet a further increase

in core body temperature

that would be associated with wakefulness,

your ability to be alert that morning

or throughout the day and so on.

It also means that if you do your deliberate cold exposure

very late in the evening or at night,

so 6 p.m., 7 p.m., 9 p.m. and so on

you are going to increase your core body temperature.

And if you recall a decrease in core body temperature

of one to three degrees is not just beneficial

but is necessary in order to get into deep sleep

and remain in deep sleep.

So the takeaway from this is

deliberate cold exposure done properly

will increase your core body temperature

and make you feel more alert.

So if you’re doing it early in the day

that’s probably terrific

given that most of us want to be alert during the day.

However, if you do it too late in the day,

evening or night, it can disrupt sleep

by way of disrupting your core body temperature.

Now, the caveat to that is I myself

tend to do my deliberate cold exposure early in the day,

maybe not first thing in the morning, but mid morning,

maybe as late as three or four in the afternoon

in some cases, in the longer days of summer

I might do it even later, 5 or 6 p.m.

and have no trouble sleeping.

I have done deliberate cold exposure very late at night,

10 p.m., 11 p.m. and so on as part of a 30 day challenge

of doing deliberate cold exposure every day for 30 days.

And I got sloppy with my timing.

And then in order to not miss a day,

I would do it at 11 o’clock at night.

And I must say, I found that I could still fall asleep

very easily, even doing deliberate cold exposure

very late at night.

However, on those particular days, I was particularly busy.

And so I was particularly exhausted

when I arrived at the deliberate cold exposure

and I had no trouble falling asleep

after doing deliberate cold exposure

and then taking a nice warm shower and then going to sleep.

But I could imagine that because of the increases

in core body temperature caused by deliberate cold exposure

that were one to do that too late in the day,

evening or night, that it could indeed disrupt your sleep.

So my recommendation would be for most people,

only do deliberate cold exposure if you are prepared

to be fairly alert for the next one to four

or maybe even six hours following

that deliberate cold exposure.

So for today’s episode, as is the case with most episodes

of the Huberman Lab Podcast, I covered a lot of material.

We talked about mechanisms of catecholamines and stress

and pulsatile release of epinephrine, metabolism,

mental effects, performance, glabrous skin cooling

and on and on and on.

And while the goal of course is to make sure

that everyone arrives at specific, very clear mechanistic

and actionable protocols, I do realize that it is

an immense amount of information.

And for that reason, I’ve created a list

of deliberate cold exposure protocols

aimed at improving mental toughness and resilience,

mood, performance, metabolism, reducing inflammation

and so on and so forth.

All of those have been condensed into succinct form

and can be found at the Huberman Lab

Neural Network Newsletter.

This is a monthly or semi-monthly newsletter

that we release that includes takeaways

from the podcast and protocols.

You can access those protocols zero cost

by simply going to hubermanlab.com,

signing up for the Neural Network Newsletter.

It’s very easy to do.

You just supply your email and you will receive

the newsletter.

We do not share your email with anybody else.

In fact, we have our privacy policy laid out

on the hubermanlab.com website.

So you can find that there.

And the protocols that I’ve designed

should make it very straightforward for you to create

a set of protocols that you could use with cold showers,

with cold immersion, with or without ice

in combination with exercise,

specifically for one goal or another

or to accomplish multiple goals simultaneously.

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So thank you once again for joining me in the discussion

about the use of deliberate cold exposure

for health and performance.

And last, but certainly not least,

thank you for your interest in science.

Thank you.